what would pressurise the cooling system?

quest96 · Post by **quest96** » Thu Dec 18, 2008 9:11 pm

Hey guys I just put another head on my 4g64 wideblock. This head is a good head. I thought my old head was warped and was causing the cooling system to become pressurised. So I replaced it with a known good head and it still is pressurising the cooling system. I have a 1st gen 4g64 wideblock and I am running the coolant out the front of the head. Any ideas on what else on these engines would pressurise the cooling system? If I let it idle I put a coolant pressure gauge on it and I saw almost 20 psi. I have a cometic head gasket on it now but I tried a stock gasket as well and it didnt help. Any ideas, you guys are always helpfull and I really appriciate any help. Thanks... Don...

Robert Venable · Post by **Robert Venable** » Fri Dec 19, 2008 12:56 am

20 psi??? Is this after it warms up and without a cooling fan on it??

quest96 · Post by **quest96** » Fri Dec 19, 2008 8:09 am

20psi while it's still warming up. If you drive the car and run it hard it will keep pushing until it overflows the coolant bottle. The rad hoses get rock hard but the car doesn't run hot and the thermostat is opening. The thermostat and the water pump are new as well. I used the eclipse waterpump.

citrus3000psi · Post by **citrus3000psi** » Fri Dec 19, 2008 9:00 am

Could it be as simple as trapped air?

quest96 · Post by **quest96** » Fri Dec 19, 2008 10:16 am

No I blead the system. When I drove the car it wouldn't push coolant out until I ran the car hard but it was still building to much. There was a post somwhere online a friend of mine was just telling me about. Somone had a turbo that was pressurising the cooling system. I have a turbonetics T3T4 ball bearing turbo that I got from ebay used. I had it rebuilt but maybe the center section is cracked. I'm gonna remove the water lines from it tonight and see what happens.

Robert Venable · Post by **Robert Venable** » Fri Dec 19, 2008 10:53 am

Sounds to me that you are just running the car hot. The Pressure is comming from the hot fluid expanding-- just like ti does in any other coolant system (aka-- thats why we have presure relieving coolant caps).

I've seen up to 25 psi in my cooling system when I disabled my coolant fan (surprising considering it is a 16 psi system with over 200k), this was simply due to the system getting hotter and hotter-- causing it to expand more and more.

If your coolant system was developing pressure in it cold-- thats when you need to worry.

Bill Hincher · Post by **Bill Hincher** » Fri Dec 19, 2008 11:32 am

pressure like that is only when compression from the cylinder is leaking into the coolant system
if your head gasket and your cylinder head is good, then you got a cracked block

citrus3000psi · Post by **citrus3000psi** » Fri Dec 19, 2008 4:44 pm

wouldn't there be signs of oil in the coolant? or vice-versa

Bill Hincher · Post by **Bill Hincher** » Fri Dec 19, 2008 8:11 pm

It probably should have oil in it , but it doesnt have to, it depends on where the cooling system is collecting the pressure from

Robert Venable · Post by **Robert Venable** » Fri Dec 19, 2008 8:49 pm

20 psi means compression leakage from combustion chamber??? Come one now. Why only 20 psi when even a horrible running engine will have 4 times that kind of compression just to run.

I know for a fact that I have seen multiple cars reach 20 psi and not have a problem with them. It is normally in newer cars that are running high coolant temps for emissions. The rad. cap on some of the cars I work on is 2 bar (aka 29.4 psi).

If you REALLY think it's combustion chamber leak-- run a leak down test and see if you get any pressure in the coolant system.

Bill Hincher · Post by **Bill Hincher** » Sat Dec 20, 2008 10:34 am

the way you test for pressure in the cooling system is by warming up your engine and allow the thermostae to open , connecting a pressure gauge in your radiator and and then allowing the engine to run.

If it has an electric coolant fan, you watch to make sure it cylces on and off, then you watch the pressure build.

If the pressure builds and then drops as the fan cycles on and off to the EXACT same pressure, then your coolant system is good

BUT if your cooling system cycles on and off with the coolant fan and continues to build pressure, you have a leak in the coolant system

the only pressure the radiator cap should have to deal with is from coolant expansion.

Coolant expansion doesnt build 20lbs of pressure

quest96 · Post by **quest96** » Mon Dec 22, 2008 8:35 am

Thanks guys thats what i'm affraid off is a cracked block. I had a coolant pressure tester on it last night and I ran out of gas. I havn't had alot of time to fool with it with chrismas coming. I'm going to run it tonight. I blead the sytem because the lower hose was still cold even though the fans were running. I'm gonna retest tonight. I'll let you know what I find........

Bill Hincher · Post by **Bill Hincher** » Mon Dec 22, 2008 9:17 am

you could have the head gasket in backwards? the lower radiator hose indicates blocked circulation

take the thremostate out and see if the lower radiater hose heats up, and dont forget, water pump impellers do come disconnected from the impeller shaft sometimes

quest96 · Post by **quest96** » Tue Dec 23, 2008 10:19 am

I checked the flow last night and when it was warming up The lower hose got hot and I could see it was circulating. I put the coolant pressure tester on and it built up about 25psi on the tester. The fans were cycling on and off. I left the pressure tester on and it holds pressure. How can I check for a cracked block?

Bill Hincher · Post by **Bill Hincher** » Tue Dec 23, 2008 5:58 pm

if there is a compression leak into the cooling system the pressure would 'grow' lets say from 10 lbs to 12 lbs, to 15 lbs , every time the fans cycle .

The amount of starting pressure doesnt matter, if you put in 10lbs, it should stay right at 10lbs everytime the fans go 'off'

the pressure will raise, then the fans go 'on' and then the pressure will fall as the fans run and then the pressure should be exactly the same as it started at when the fans go 'off'

If that is happening, then your block/head/gasket are ok, the next step is curculation, test the radiator and make sure its the same temp from top to bottom, it may be plugged, or pull the water pump and make sure the impeller is on the shaft ok

coltboostin · Post by **coltboostin** » Tue Dec 23, 2008 6:39 pm

Im just tossing out options that have not been said-

Block warped?

Cylinder wall cracked? (common on 2.4s)

quest96 · Post by **quest96** » Wed Dec 24, 2008 8:09 am

I had the block decked when it was built. The water pump is new as well. When it warms up it starts building pressure. If I run it with the cap off You can see it circulating.

citrus3000psi · Post by **citrus3000psi** » Wed Dec 24, 2008 9:30 am

Do a leak down test and see if it its truely a combustion leak.

Bill Hincher · Post by **Bill Hincher** » Wed Dec 24, 2008 11:07 am

take a spark plug reading and see if you have a 'white' electrode, thats coolant

if one is real clean, thats another sign of coolant

quest96 · Post by **quest96** » Sat Dec 27, 2008 12:56 am

I'll check the plugs tomorow. I used a combustion gas tester on it today I didn't see much change in color but it turned slightly green. I had it hot and running with the cap off when I reved the engine the coolant was flowing and it got foamy and would spew out of the radiator. Has anyone used a fwd water pump on the rwd swap? I'm pretty sure they rotate the same direction.

Bill Hincher · Post by **Bill Hincher** » Sat Dec 27, 2008 10:46 am

do you have a pic of your set up? did you stay with the rear exit on the thermostate?

peregrine · Post by **peregrine** » Sat Dec 27, 2008 6:52 pm

you got a cracked block. magnaflux FTW.

quest96 · Post by **quest96** » Mon Dec 29, 2008 8:53 am

front exit on the T-stat.