Overheated on track - now what?

[infernosg]

Overheated the car at Mid-Ohio during HPDE. 7th run of the weekend, 3rd of the day; ambient temperatures around 80F. Coming out of the esses (medium-speed, hard right turn, slightly uphill) in 3rd gear around 5000 RPM the low coolant buzzer went off and the temperature gauge started climbing. Let off and limped into the pits with the heater blasting but the gauge still got to "H". Spent no more than 5 minutes at that condition and did not exceed 3000 RPM during that time. Shut down and there was coolant boiling and steaming out of the overflow bottle. Once cooled off added water to the radiator - didn't take too much initially but the low coolant buzzer kept going off so kept bleeding the system and adding more water. Made the 2.5 hour drive home with no overheating issues but at lower speeds and/or tighter corners the low coolant buzzer would sound and then go off after a while. Added more water last night and drove the car to work today with no buzzer or overheating.

Some observations from before/after:
-Cooling system was flushed June 2010. 60/40 distilled water/anti-freeze mixture with a touch of Redline Water Wetter.
-Since Friday night there's been a high-pitched squealing only during low-speed deceleration. Sounds like belt squeal but goes away as soon as the clutch is pushed in or I get back on the gas. The "adjuster bolt" on the airpump sheared off so it is being held in place by the "lock bolt". Belt seems tight.
-Prior to the run was more coolant in the overflow bottle than usual.
-Prior to the run I had a hard time starting the car. Did the flooded engine start procedure and it limped to life with a little backfiring but idle was steady once warmed up.
-I changed my shifting plan that session - I only went into 4th at one point on the track, rather than three. Engine speeds were almost always above 5000 RPM, but never exceeding 7500 RPM.
-This morning it started a little harder than usual and the engine sounds a little "different" during decel. If in neutral and revved it almost sounds like a 'hissing" noise as engine speed drops but it goes away when it hits idle speed.
-No white smoke, no power loss or any other driveability issues that I can discern.

I know I need to flush and fill the system again - need to get the tap water out of there. Next will be an attempt to replace the sheared adjuster bolt in the airpump and then replace all the belts, but then what? Inspect/replace thermostat? Waterpump? Why did the low coolant buzzer keep coming on and going off? Most importantly, is the engine fried?

For the people who track their FC's is this a result of water pump cavitation? Time for an underdrive pulley of some sort? Time to upgrade the radiator?

[vex]

Originally Posted by infernosg

Overheated the car at Mid-Ohio during HPDE. 7th run of the weekend, 3rd of the day; ambient temperatures around 80F. Coming out of the esses (medium-speed, hard right turn, slightly uphill) in 3rd gear around 5000 RPM the low coolant buzzer went off and the temperature gauge started climbing. Let off and limped into the pits with the heater blasting but the gauge still got to "H". Spent no more than 5 minutes at that condition and did not exceed 3000 RPM during that time. Shut down and there was coolant boiling and steaming out of the overflow bottle. Once cooled off added water to the radiator - didn't take too much initially but the low coolant buzzer kept going off so kept bleeding the system and adding more water. Made the 2.5 hour drive home with no overheating issues but at lower speeds and/or tighter corners the low coolant buzzer would sound and then go off after a while. Added more water last night and drove the car to work today with no buzzer or overheating.

Some observations from before/after:
-Cooling system was flushed June 2010. 60/40 distilled water/anti-freeze mixture with a touch of Redline Water Wetter.
-Since Friday night there's been a high-pitched squealing only during low-speed deceleration. Sounds like belt squeal but goes away as soon as the clutch is pushed in or I get back on the gas. The "adjuster bolt" on the airpump sheared off so it is being held in place by the "lock bolt". Belt seems tight.
-Prior to the run was more coolant in the overflow bottle than usual.
-Prior to the run I had a hard time starting the car. Did the flooded engine start procedure and it limped to life with a little backfiring but idle was steady once warmed up.
-I changed my shifting plan that session - I only went into 4th at one point on the track, rather than three. Engine speeds were almost always above 5000 RPM, but never exceeding 7500 RPM.
-This morning it started a little harder than usual and the engine sounds a little "different" during decel. If in neutral and revved it almost sounds like a 'hissing" noise as engine speed drops but it goes away when it hits idle speed.
-No white smoke, no power loss or any other driveability issues that I can discern.

I know I need to flush and fill the system again - need to get the tap water out of there. Next will be an attempt to replace the sheared adjuster bolt in the airpump and then replace all the belts, but then what? Inspect/replace thermostat? Waterpump? Why did the low coolant buzzer keep coming on and going off? Most importantly, is the engine fried?

For the people who track their FC's is this a result of water pump cavitation? Time for an underdrive pulley of some sort? Time to upgrade the radiator?

I hate to say this, but it sounds quite similar to a soft seal letting go. You might want to let the engine sit for a day or two and check to see if you have any pooling coolant in the combustion chamber.

When mine let go I could easily start it up and run it around town, but as soon as it hit operating temperature the engine would start to run on one rotor. When temperatures got warmer the car got harder and harder to start.

Also pay attention to dropping coolant levels. You may have a link somewhere (whether it's by the water pump housing, a hose, or internal of the engine).

[88turboii]

it was opposite for me when i had bad coolant seal. it would run on one rotor at start, but after about 15 seconds or so it would run like normal. white smoke on startup, from the coolant puddling in the chambers burning off. that and i could fill the overflow container with a couple 3rd gear pulls lol

but yeah i also have overheating problems on the track. it will start creeping past 1/2 way after about 10 minutes of track time, even in cool weather. im still running a tmic, so the radiator should be getting plenty of flow. it was suggested to me to use aluminum tape and seal off all the parts around the radiator that air could get past, but i have not tried that yet

[infernosg]

Originally Posted by vex

I hate to say this, but it sounds quite similar to a soft seal letting go. You might want to let the engine sit for a day or two and check to see if you have any pooling coolant in the combustion chamber.

I assume I check this by pulling the EGI fuse and a spark plug and cranking the engine to see if anything comes out? Spark plugs are also something I need to check.

Originally Posted by vex

When mine let go I could easily start it up and run it around town, but as soon as it hit operating temperature the engine would start to run on one rotor. When temperatures got warmer the car got harder and harder to start.

I drove 2.5 hours back home yesterday at speed >70 mi/hr and I'm positive I didn't loose a rotor, or any power for that matter. If I do have a failed coolant o-ring or rotor housing, it must be very small. The weird thing about the hard starting is that it was easier to start it this morning (ambient temperatures ~65F) after sitting all night than it was yesterday afternoon (ambient temperatures ~80F) after only sitting for ~3 hours.

Originally Posted by vex

Also pay attention to dropping coolant levels. You may have a link somewhere (whether it's by the water pump housing, a hose, or internal of the engine).

I have no found any large external leaks, but that doesn't mean much. When I flush the system this weekend I'll get a much better idea of what kind of shape everything is in. As far as I know the radiator, cap and water pump are all original OEM equipment. I'm pretty sure the thermostat was replaced at some point and if it was I'm almost positive it is not an OEM part.

In the meantime I guess I'll just keep an eye out on the coolant level. The coolant level sensor seems overly sensitive to me, but it hasn't come back on in a while. If nothing changes I can only conclude the conditions simply outmatched the car's 22 year-old cooling system and some upgrades are in order.

Originally Posted by 88turboii

it was opposite for me when i had bad coolant seal. it would run on one rotor at start, but after about 15 seconds or so it would run like normal. white smoke on startup, from the coolant puddling in the chambers burning off. that and i could fill the overflow container with a couple 3rd gear pulls lol

Would the white coolant-smoke and smell make it past two catalytic converters? Aside from Magnecor spark plug wires and a K&N drop-in filter my engine is all stock. The exhaust was replaced after the manifold at some point but it looks to be a stock replacement, not a performance modification. I only ask because I see no smoke and don't smell coolant at the tailpipes.

Originally Posted by 88turboii

but yeah i also have overheating problems on the track. it will start creeping past 1/2 way after about 10 minutes of track time, even in cool weather. im still running a tmic, so the radiator should be getting plenty of flow. it was suggested to me to use aluminum tape and seal off all the parts around the radiator that air could get past, but i have not tried that yet

I was about 20 minutes into the session - literally the last lap before cool-down. As far as I know, this is the only time the gauge crept past 1/2 way during all of the sessions. When I heard the buzzer I looked at the gauge and it was just then starting to move from 1/2 way to "H" - it's not like I ran a full lap at WOT with the gauge pegged at "H".

[vex]

Originally Posted by infernosg

I assume I check this by pulling the EGI fuse and a spark plug and cranking the engine to see if anything comes out? Spark plugs are also something I need to check.

If you were closer I'd lend you my bore scope (makes checking things really easy). But yes, you can do it that way too.

I drove 2.5 hours back home yesterday at speed >70 mi/hr and I'm positive I didn't loose a rotor, or any power for that matter. If I do have a failed coolant o-ring or rotor housing, it must be very small. The weird thing about the hard starting is that it was easier to start it this morning (ambient temperatures ~65F) after sitting all night than it was yesterday afternoon (ambient temperatures ~80F) after only sitting for ~3 hours.

Which makes sense if you have a casting give way.

I have no found any large external leaks, but that doesn't mean much. When I flush the system this weekend I'll get a much better idea of what kind of shape everything is in. As far as I know the radiator, cap and water pump are all original OEM equipment. I'm pretty sure the thermostat was replaced at some point and if it was I'm almost positive it is not an OEM part.

In the meantime I guess I'll just keep an eye out on the coolant level. The coolant level sensor seems overly sensitive to me, but it hasn't come back on in a while. If nothing changes I can only conclude the conditions simply outmatched the car's 22 year-old cooling system and some upgrades are in order.

Sounds like a plan.

[RETed]

Originally Posted by infernosg

Spark plugs are also something I need to check.

This should tell you if the engine is bad or not.
No sense guessing everything else unless you get confirmation...


-Ted

[infernosg]

Originally Posted by RETed

This should tell you if the engine is bad or not.
No sense guessing everything else unless you get confirmation...


-Ted

When it stops raining this is my plan - I'll even post pictures when I'm done. I suppose with coolant/water I'm looking for a white/yellow fouled plug?

The car started and ran just fine after work yesterday. No buzzer, no overheating, no weird noise (other than loose belts). Letting is sit for today and I'll see what it does tomorrow morning (pending plugs).

Is it possible the slightly loose airpump belt was not providing enough friction on the water pump and it was slipping at higher RPM?

[RETed]

Originally Posted by infernosg

When it stops raining this is my plan - I'll even post pictures when I'm done. I suppose with coolant/water I'm looking for a white/yellow fouled plug?

Not necessarily...

Typically, if coolant is leaking into the chamber, the spark plug is going to come out clean - it's like if you're running water injection.
If you have the leading versus trailing plugs next to each other, it'll be obvious.


-Ted

[infernosg]

Well I'm pretty sure the engine needs a rebuild, but more on that later. First, spark plug pictures. Rotor 1 first, then rotor 2. Leading is on left, trailing is on right.





So I'm not sure how to read those but I don't think it matters. They weren't wet or anything but you can see the white/brown build up.

Per some suggestions I pulled the EGI fuse, removed the radiator cap and had my wife crank the car with the throttle open. After a few bubbles the fluid level began to rise. After putting everything back together and driving around the block for a bit I noticed that I'm getting a good amount of bubbles coming out of the overflow tube into the overflow bottle. Occasionally there would be periods where some amount of coolant would come out of this tube. Additionally, the upper radiator hose is "hard" when the car is running. Right before I turned the car off the low coolant buzzer came on again. Correct me if I'm wrong, but this all seems to indicate at least a failed water seal and the combustion gases are partially pressurizing the cooling system.

[RETed]

The spark plugs don't look like there's any obvious sign the engine is burning coolant.

With that said, if it's a small coolant leak into the engine, it will not show on the plugs.
Also, failure of the water jacket o-ring could make it possible it won't show on the spark plugs.

The low coolant buzzer triggering could be just because you opened the cap and compromise the cooling system - allowing some air to stay trapped and then trigger the buzzer.

I'm trying to be optimistic at this point.

The only way to tell is to drive it a significant distance and then check the coolant level to see if it significantly dropped (or puked out the overflow).


-Ted

[Pete_89T2]

I agree with Ted on this. The coolant level sensor is pretty sensitive, and when you flush & fill the cooling system, it takes lots of "burping" to get all the trapped air out of the system.

If you can get your hands on a cooling system pressure tester, you can do a quick pressure test to verify if you have a leak or not and find it. Basically this is a quick pressure leak down test - remove the radiator cap, replace it with pressure tester's cap, pump it up to the recommended pressure and watch its gauge for 10~15 minutes. If the pressure drops, you've got a leak - external leaks will be found wherever you see coolant peeing out; internal leaks may not be as easy to find, but if the pressure drops you've got a problem.

Check with your local auto parts chain shop or tool rental shop - you can probably rent a pressure tester for a reasonable cost; just have to make sure they have one with the right cap to fit your radiator.

[infernosg]

After the first "event" I filled up the radiator and managed to drive 2.5 hours home averaging 70 mi/hr with no overheating, but the buzzer would come on occasionally during tighter turns and lower speed driving. Once I got home and the car cooled off I topped off the radiator and bled the system the best I could. At this point the radiator was completely full and the overflow bottle was at the full level as well. I was able to drive to and from work (only 8 miles) with no issues on Monday and I let the car sit most of the day yesterday. Yesterday afternoon, after driving more recklessly than I'd like on the street, I came home and revved the engine in neutral in the driveway. No buzzer while doing all this so I turned it off and let it sit for about 30 minutes. Before starting it up again I noticed the overflow bottle was now ~1" above the "full" mark. I made it to the end of the driveway when the buzzer came on. Since it was still fully warmed up I just pulled back up and turned it off for good. The buzzer did go off as soon as I started to move back up the driveway.

What has me most worried is the constant bubbling I'm getting in the overflow bottle. To ensure it wasn't be caused by engine vibrations I removed the overflow cap and tube and placed it in a cup of clear water. With the car fully warmed up there was a constant stream of tiny bubbles coming out of the pickup tube. Only once did a moderately large amount of coolant get burped into the cup. After that it was back to the bubbles.

Pressure testing is my next step before throwing new parts at it (rad. cap, thermostat, water pump). The plan is to swing by an auto parts store after work to see if they have anything I can rent.

The one thing I can't seem to explain is the original overheating event. IIRC, the cooling system holds like 2 gallons of water and I know I didn't add nearly that much after it overheated. The fact the buzzer came on just as the temperature gauge started to rise also has me stumped considering it has come on many times since that and the temperature gauge hasn't moved.

Originally Posted by RETed

I'm trying to be optimistic at this point.

I am a self proclaimed pessimist and worry constantly, but I'm trying!

[Pete_89T2]

Originally Posted by infernosg

After the first "event" I filled up the radiator and managed to drive 2.5 hours home averaging 70 mi/hr with no overheating, but the buzzer would come on occasionally during tighter turns and lower speed driving. Once I got home and the car cooled off I topped off the radiator and bled the system the best I could. At this point the radiator was completely full and the overflow bottle was at the full level as well. I was able to drive to and from work (only 8 miles) with no issues on Monday and I let the car sit most of the day yesterday. Yesterday afternoon, after driving more recklessly than I'd like on the street, I came home and revved the engine in neutral in the driveway. No buzzer while doing all this so I turned it off and let it sit for about 30 minutes. Before starting it up again I noticed the overflow bottle was now ~1" above the "full" mark. I made it to the end of the driveway when the buzzer came on. Since it was still fully warmed up I just pulled back up and turned it off for good. The buzzer did go off as soon as I started to move back up the driveway.

The 1" extra coolant in the overflow bottle 30 minutes after a hot shutdown sounds about normal. When you shut down the engine the radiator cap allows pressurized/expanding coolant to flow into the overflow tank, raising its level. When the system cools down enough, the resulting vacuum should suck the coolant back into the radiator, leaving the overflow bottle around the full mark.

Originally Posted by infernosg

What has me most worried is the constant bubbling I'm getting in the overflow bottle. To ensure it wasn't be caused by engine vibrations I removed the overflow cap and tube and placed it in a cup of clear water. With the car fully warmed up there was a constant stream of tiny bubbles coming out of the pickup tube. Only once did a moderately large amount of coolant get burped into the cup. After that it was back to the bubbles.

If air is getting into the system, from either a leaky radiator cap or anywhere else in the system, it could explain the bubbles you're seeing. And it would explain the added difficulty in getting the system fully "burped" and keeping the buzzer quiet.

Originally Posted by infernosg

Pressure testing is my next step before throwing new parts at it (rad. cap, thermostat, water pump). The plan is to swing by an auto parts store after work to see if they have anything I can rent.

If you're going to throw parts at it, I'd suggest getting a new Mazda radiator cap & thermostat regardless, especially if you don't know what's in there now. Don't bother buying a Stant or aftermarket thermostat - for some reason the ones the make for rotaries are crap.

Originally Posted by infernosg

The one thing I can't seem to explain is the original overheating event. IIRC, the cooling system holds like 2 gallons of water and I know I didn't add nearly that much after it overheated. The fact the buzzer came on just as the temperature gauge started to rise also has me stumped considering it has come on many times since that and the temperature gauge hasn't moved.

If your system is all stock, the cooling system is barely sufficient for track duty - it has very little excess cooling capacity, and a just a little bit of pump cavitation due to the prolonged high revs can easily boil things over. The buzzer sensor needs to be immersed in coolant at all times to keep it quiet - just one air bubble under it and BUZZZZZZZZZ. The temperature of the coolant has no effect on the buzzer - it's a level sensor.

[infernosg]

Originally Posted by Pete_89T2

The 1" extra coolant in the overflow bottle 30 minutes after a hot shutdown sounds about normal. When you shut down the engine the radiator cap allows pressurized/expanding coolant to flow into the overflow tank, raising its level. When the system cools down enough, the resulting vacuum should suck the coolant back into the radiator, leaving the overflow bottle around the full mark.

When I get home I'll check it out again to see if it went down. I know the radiator pulled a good amount back in at the track as it cooled down, which isn't looking too good for the "there's a leak somewhere" theory.

Originally Posted by Pete_89T2

If air is getting into the system, from either a leaky radiator cap or anywhere else in the system, it could explain the bubbles you're seeing. And it would explain the added difficulty in getting the system fully "burped" and keeping the buzzer quiet.

I have noticed there is a tiny tear in one of the rubber seals in the radiator cap. I though it too small to make a difference but who knows. I always figured with the car running the pressure generated by the water pump would be more than sufficient to keep air from being sucked in, even at idle. If air is getting into the system with the car off, I'd expect to see the bubbles stop at some point as well.

Originally Posted by Pete_89T2

If you're going to throw parts at it, I'd suggest getting a new Mazda radiator cap & thermostat regardless, especially if you don't know what's in there now. Don't bother buying a Stant or aftermarket thermostat - for some reason the ones the make for rotaries are crap.

This I know. The rad. cap is the original I believe, but I'm almost certain the thermostat was replaced at one point (I have the records from the previous owners) and it's likely it's not an OEM Mazda unit. I'll do the pressure test and if that passes, change the radiator cap and go from there. If it fails, well I've got some exploring to do...

Originally Posted by Pete_89T2

If your system is all stock, the cooling system is barely sufficient for track duty - it has very little excess cooling capacity, and a just a little bit of pump cavitation due to the prolonged high revs can easily boil things over. The buzzer sensor needs to be immersed in coolant at all times to keep it quiet - just one air bubble under it and BUZZZZZZZZZ. The temperature of the coolant has no effect on the buzzer - it's a level sensor.

Yep, cooling system is all stock. I had no issues during the other runs over the weekend but I did stay in 3rd gear a lot more for this particular run so perhaps that was the proverbial straw. Aside from an upgraded radiator what other modifications would bring the cooling system up to track-ready levels? It's not a track-only car and I maybe drive it 25% of the time. I've seen underdrive main pullies but those make me nervous with the stock alternator's output.

Is there any way to "officially" bleed the S5 cooling systems? I open up the heater, turn the car off, then fill the radiator and overflow bottles. I squeeze the upper radiator hose to get as many air bubbles out as possible.

[Pete_89T2]

Originally Posted by infernosg

I have noticed there is a tiny tear in one of the rubber seals in the radiator cap. I though it too small to make a difference but who knows. I always figured with the car running the pressure generated by the water pump would be more than sufficient to keep air from being sucked in, even at idle. If air is getting into the system with the car off, I'd expect to see the bubbles stop at some point as well.

Definitely replace the cap with a new Mazda cap then. If it's not sealing properly, it won't hold its rated pressure, and this in turn will make it more likely to boil over.

Originally Posted by infernosg

This I know. The rad. cap is the original I believe, but I'm almost certain the thermostat was replaced at one point (I have the records from the previous owners) and it's likely it's not an OEM Mazda unit. I'll do the pressure test and if that passes, change the radiator cap and go from there. If it fails, well I've got some exploring to do...

If it's not a Mazda T-stat, I'd just replace it. The Mazda T-stat & gasket for it is pretty cheap, like under $15

Originally Posted by infernosg

Yep, cooling system is all stock. I had no issues during the other runs over the weekend but I did stay in 3rd gear a lot more for this particular run so perhaps that was the proverbial straw. Aside from an upgraded radiator what other modifications would bring the cooling system up to track-ready levels? It's not a track-only car and I maybe drive it 25% of the time. I've seen underdrive main pullies but those make me nervous with the stock alternator's output.

Besides an upgraded radiator, just make sure the fan shroud and all the ducting is in place & functional, including the plastic undertray. Key point here is to make sure that air only flows thru the radiator & oil cooler, and not around them. As for the fan, it only matters when you're at idle or driving at low speeds, but just check it per the FSM procedure to verify the clutch on it works - when it's hot, fan should turn but resist freewheeling when you try to spin it by hand. The underdrive pulleys will help reduce waterpump cavitation at high RPMs on your track days, and if paired with a similarly sized underdrive alternator pulley (i.e., to keep the drive ratios the same/close to stock pulleys) would solve any alternator output issues. Anything else is just maintenance - flush out your system regularly, use fresh coolant & distilled water at proper mix for your climate, check/replace all hoses as required.

Originally Posted by infernosg

Is there any way to "officially" bleed the S5 cooling systems? I open up the heater, turn the car off, then fill the radiator and overflow bottles. I squeeze the upper radiator hose to get as many air bubbles out as possible.

Not that I can find in the FSM. What I do whenever I flush & fill the system is make sure the heater is set to full heat before starting, and after I do the initial filling of the radiator with coolant, I'll let it idle with the rad cap off. When the engine reaches operating temp and the upper hose is hot to the touch, I'll run the engine in neutral at a constant 2~3K RPMs for a couple of minutes, then I'll quickly rev the engine up past 5K & back down to idle a few times, still with the cap off. When the level in the radiator drops (it will as trapped air pockets escape), add more coolant till its full. While you're doing this drill, the coolant level buzzer will sound off from time to time - it's normal. I keep repeating this process until I can't add any more coolant to the radiator. Then I top off the overflow tank with coolant to the full line, put the radiator cap back on, and take it for a drive. Let it cool down fully, check the level in the overflow tank, add coolant if needed to get it back to the full mark.