Dumping Antifreeze after the engine is off.

[4g63mightymax]

I just got my 4g63 truck running nicely at a very normal, middle of the gauge, temperature. It has never overheated, or even come close, but when I turn the truck off, it immediately dumps boiling antifreeze into the overflow bottle from the thermostat housing. For some unknown reason there is pressure building up near the thermostat the moment the engine shuts off. With the engine off, I can watch the temp gauge slowly go from the middle of the gauge to the bottom (it doesnt heat up once turned off). I have made sure there weren't any air bubbles, and replaced one radiator cap with no success. I also made a heat shield for my upper radiator hose, just in case it was getting radiant heat from my manifold. I did move a lot of water lines around during this engine swap so I am wondering if I put one in the wrong location, causing the problem. Does anybody have any ideas? Would it help if I describe where all the water lines come and go?
Pretend that it is a stock 1991 4G63 having this problem. What ideas do you guys have?
Thanks in advance.
Jeremy

 

[andymoraitis]

Jeremy,

I know you replaced the radiator cap, but did you change the thermostat? I would try a 180 if you haven't. Barring that, the issue is either related to water line routing or the headgasket isn't sealing properly. I've seen issues before where base timing was set incorrectly and the motor was actually at 15 degrees BTDC instead of 5 whcih resulted in severe pre-ignition and loss of seal on the headgasket. The results were similar to yours in that the motor pushed coolant even though the gauge never went over 1/2. Other things I'd check are:

1. Coolant temp sensor
2. Make sure the system is properly purged of air bubbles.

Instead of describing your water line routing, it would be great if you could take a number of pictures and post them so that we have a visual reference.

Keep us posted,

Andy

 

[Old Mitsu Tech]

Are you having to add anti freeze all the time?

 

[4g63mightymax]

Andy, Old Mitsu Tech,
First off, thank you for the response!
The engine has a new head gasket, and completely rebuilt head (I bought it with bent valves). It has a new thermostat in it, but I am not sure what the temperature rating on it is. My datalogger does say that my coolant temp sensor for the ECU is reading -75 degrees F. So I am sure the engine is running rediculously rich. I am going to try and get that fixed this weekend, and it does have a new coolant temp sensor as well. Earlier this week I parked the truck on a steep hill and jacked up the front of it to try and purge out any air bubbles. I am going to try that again as well this weekend, because it really does act like there is air in there. I did check my timing and I am currently set to 5 degrees BTDC with the timing wire grounded. Keep in mind, it doesn't push out any antifreeze while it is running, and it seems to run at a very normal temperature. But the second the engine is turned off, it starts pumping out antifreeze into the overflow bottle. You can see a lot of pictures of the built on my website www.hotrodcoffeeshop.com. There are plenty of engine pics, but none specifically of the water lines. I will take some pictures of the water lines specifically and post them. It make take me a day or two though, because I wont be able to do it tonight.
Any other tips, tricks or ideas?
Thanks
Jeremy

 

[andymoraitis]

I'd start it cold with the rad cap off and let the thermostat open fully to purge any excess air, add coolant and re-cap it. That seems to be a good place to start if everything else we mentioned appears to be working properly. Aside of that, you may want to try a 16psi radiator cap if you haven't tried that already. Oh and fix that coolant sensor!

 

[Talontsi150]

I was going through the same problems with my car. The gage would only make it to normal temps, but once I turn off the car, it would push out boiling antifreez... All this started when I bent the valves in my head, had the head repair with new valves. Thats when I started seeing the antifreez boil out the overflow... First check your spark plugs and see if there's any type of rust around them.. If you see rust around the bottom of the plug then your head has hair line cracks in it. Probably not what you want to hear!! You know whats crazy, my car ran fine, I pull 11.20's @ the track also put out 500+hp on the dyno. The signs I was getting on the dyno was after every pass, the overflow would push out antifreez with lots of steam pressure, at the track, every pass I made I had to put water back in the radiator.. Crazy part is that the car never blew white smoke... Go figure. Hopes this all makes sense, i'm @ work sneaking on the net... Oh yeah one more thing, Check you head studs, make sure they are tighten to spec's.

Marc

 

[project_tsi]

Does it only do it after you boost? Try just putting around and see if it still dumps coolant. If it only does it after boosting/spirited driving, my vote is for a popped HG, warped head, etc.

 

[GstRacer]

hey man i believe my cars doing the exact some thing, when i turn it off the coolant sounds and is boiling inside the motor for a little while after. but when i drive it stay really cool. like 180. i took my thermostat out witch is a 180 brand new not even 2500 miles on it drilled 3 holes in the outside ring to see the diff. well it drives real cool and it does open up i purged the system, but w holes in the t stat it should not matter i think. the motors brand new, head block gasket arp head studs only like 2100 miles on it. no overheating when i drive in boost or not. WTF is it ??

 

[4g63mightymax]

I am pretty sure the problem has been solved. After messing with the truck for a while over the last 2 days, I got a big burp from the cooling system, releasing a large air bubble. The engine hasn't dumped antifreeze since. I have warmed it up and cooled it down 3 times successfully with no coolant loss. Drilling the thermostat is an interesting idea though, maybe my engine will stay a little cooler tha way. hmmmm
Who would have thought a bubble of air would cause such stress for a week?
Thank you to all that helped! Now on to my next problem....
-Jeremy

 

[andymoraitis]

I'm glad it was something simple Jeremy. Thanks for updating your thread so that future searches will show others what caused your issue and what resolved it.

 

[GstRacer]

well i guess i will have to burp it again

 

[4g63mightymax]

I cant recommend burping enough. Once you have done it again, let us know if it worked.
-Jeremy

 

[Auto RS T]

hey man i believe my cars doing the exact some thing, when i turn it off the coolant sounds and is boiling inside the motor for a little while after. but when i drive it stay really cool. like 180. i took my thermostat out witch is a 180 brand new not even 2500 miles on it drilled 3 holes in the outside ring to see the diff. well it drives real cool and it does open up i purged the system, but w holes in the t stat it should not matter i think. the motors brand new, head block gasket arp head studs only like 2100 miles on it. no overheating when i drive in boost or not. WTF is it ??

I drill a hole in all t-stats when I install them, only pencil tipped sized though. Most aftermarket t-stats don't have the vent. If you look at most factory t-stats they have a small vent in them also. No comlplaints

I really feel this is a good way to relieve trrapped air, without affecting performance.

 

[Defiant]

i took my thermostat out witch is a 180 brand new not even 2500 miles on it drilled 3 holes in the outside ring to see the diff.

Holes that big are the same as a leaking thermostat. It probably won't reach running temperature in the winter.

 

[GstRacer]

ya i dont drive mine in the winter, too much money involed. its a brand new fully bulit motor and tranny.