thats something I haven't thought of. I will fill the system from the highest point and see what happens. I have 2 radiator caps. one in the front and one on top ot the waterpump fill neck. The one up front has leaked before. maybe I need a higher pressure cap up front?

how do you perform a propper pressure test?

This may be a very dumb question, but when you first start a car and the thermostat is closed so that the engine can warm up, what happens to all the coolant that the water pump is still trying to push? Seems like it has no where to go since it is not looping through until the thermostat opens.

I always wondered that too.

I guess it just cavitates withing the water pump housing until the thermostat pops.

:dunno:

The lower the pressure in the system the better... to a certain extent based on the coolant you're using. 13psi is what I'm using.

You want to bleed the system at the highest point last. Something you might want to add to the system is an expansion tank, I swear by them now. Installed properly they will automatically and constantly bleed the system unless there is an air bubble big enough to jam up the waterpump. If that happens you're screwed and the temp will just skyrocket. With air in the waterpump, the coolant will not move at all.

With a proper pressure tester. With the car cool, hook this little tool up to the rad cap, which ever one, and pressurize the system to 110% of the cap and watch for the leaks.

it flows through the heater core (if it's open) and weeps through the t-stat.

Originally Posted by craig3x
This may be a very dumb question, but when you first start a car and the thermostat is closed so that the engine can warm up, what happens to all the coolant that the water pump is still trying to push? Seems like it has no where to go since it is not looping through until the thermostat opens.

"it flows through the heater core (if it's open) and weeps through the t-stat".

hmmm, but I don't have a heater core. And I guess my question is that if I installed one of those fancy 50gph electric pumps, what would happen when the thermostat is closed? sounds like major pressure build up???

Then you would need to route the outlet on the back of the iron (near the oil press sensor, and create a bypass after the thermostat (see the bottom of an FC radiator. The little hose is the heater return.

Or wire it so that it doesn't come on until your t-stat is open

wouldn't no water flow create weird hotspots in the engine?

I use a 16 psi cap. Coolant Pressure is related to the temperature of the coolant. As the coolant gets hotter it builds up more pressure. if your cap is old and weak or rated too low for your application the water will escape, this means it's not cooling the engine. Usually you have a water reservoir that catches the water, and when the coolant cools it sucks it back in. If you run a cap pressure too high, this puts extra pressure on the coolant hoses and seals under overheat conditions. I prefer to run a higher then stock pressure cap, this insures the coolant is still trying to cool the engine if temps ever do get high.

A system under normal operating temps will have the same pressure with a 16 psi cap as it will with a 13 psi cap. The only difference is when the temps go higher the 13 psi will boil over quicker.

hope this helps. And given your somewhat complicated system I wouldn't be surprised if you have air in your system. There is a special coolant burping funnel that is supposed to work well for this. I would try to burp your system over several days to insure no air is in there.

Also most all cooling systems that i know of have a bypass, either external or internal. Usually they are always open. this allows the coolant to still circulate around in the engine resulting in a more uniform temperature across the whole engine, which aids efficiency and reduces wear on internal parts. Otherwise you would end up with certain spots much hotter then others, and who's to say the coolant where the Tstat is located would ever get hot enough to open before damage occurs somewhere else?

Maybe but not much more than a stock system

Not really, it'll still cool the engine, it will just allow the coolant to boil at a lower temp. But a 50/50 mix under 0 pressure will boil @ ~225*, add ~15lbs to it and it rises to ~270*, roughly 3*/lb so a 13 psi cap will allow boiling to occur @ ~265* If you ever get to 265*, you have other issues. The extra 2psi on the cap really doesn't do anything for better cooling except place more stress on the hoses/seals as you pointed out.

True, but as I said above, that extra 2psi in the cap really isn't doing anything for us.

This I will disagree with, how can a system have the same pressure if it has two different psi caps? When the pressure reaches 13psi, the 13psi cap will allow fluid to escape while the 16 psi cap will hold pressure much longer. I could run a 0 psi cap if I wanted becuase my temps never get that high. However, if they did get to ~225, my coolant WOULD boil unless I had some addition pressure in the system.

I've seen that, never needed to use it, have a few friends that have but had no luck. A different approach would be to use an expansion tank. I swear by those now and will never build another car without one. It basically works as that burping funnell does constantly, every time you start and run the car.

They will have the same pressure until the lower rated cap allows coolant to boil over. The PSI rating of the cap has no effect on the pressure until the pressure overcomes the cap.

right, and the extra ~10* of cooling before the coolant starts to boil is of no need to us. Basically there is no need to run a 16psi cap if you're using a 50/50 mix. To me the extra 3psi places on the seals/hoses isn't worth it. Hell, I think we should all be running Evans, but I pull my motor too often for that :rofl:

hope this helps. And given your somewhat complicated system I wouldn't be surprised if you have air in your system. There is a special coolant burping funnel that is supposed to work well for this. I would try to burp your system over several days to insure no air is in there.[/QUOTE]

you're right. I did have air in it from a previous boil over. I filled it on the side of the road, but didn't "burp" it. Thanks. However, I still think I may have a problem by trying to use a stock waterpump to push coolant through about 12 ft of hoses