Well, I've never seen this one before in over 10 years of dealing with these cars

New t-stat, low mileage water pump. I will say the WP might be failing, I noticed evidence of some leakage from the weep hole underneath the pulley.

Deleted AST, Blitz 1.3 bar cap.

This just started recently with zero changes made inside the engine bay. When the car is stone cold (let sit overnight) and I remove the filler cap, I'm greeted with cold pressurized coolant spraying out into my (previously) clean engine bay.

I swapped to an OEM 0.9 bar cap, doesnt seem to help.

The car runs fine, with proper coolant temps. If I just left the damn cap on I guess I wouldnt have to worry about anything

 

Rich, I have to ask, you do have a TII style cap for the filler neck? i.e. you didn't purchase one of the fancy FD caps since without the AST you need to use the TII type caps.

 

Hey Kyle,

I had been running the Blitz FD cap with the AST delete for around 3 years with no issues.

On the hypothesis that perhaps the Blitz cap was failing, I just installed the cap that came with the AST delete last night. Let the car warm up at idle and sit overnight, same problem.

Edit: I also inspected the coolant hose going to the overflow and it appears fine with no kinks.

 

Having a similar problem myself, for some reason my FD coolant system is pressurising itself and pumping all the coolant into the overflow, but I have pressure tested the engine when cold and have no leaks at all so the o-rings are good. I should point out the first run is fine but when I go to drive the car after one hot cycle it overheats and the rad fills up with air making it cool?

I have an FC filler neck and have a new water pump and new thermostat and new water pipes! I have tried another FC filler neck and a 0.9 and a 1.3 bar cap and still the same symptoms! Also have deleted the heater matrix and blocked off the pipes from the block. The rad heats evenly across the top - I'm really stuck! Apologies for jumping on the thread but symptoms seem very similar.

 

I think it's time for the funnel test. Hopefully that's negative, but at least you can start ruling out the bad things.

 

Hi Ben,

no worries man, but the symptoms are very different. My system is not filling the overflow----it's simply holding the pressure.

I checked that as well and no 'champagne' bubbles. It's a fairly fresh build (just over 1000 miles) and I have yet to see that problem with any engine I've built so I was glad to rule that out

 

I was wondering for people with the FC filler neck how the overflow can pull the coolant back into the engine, since the cap requires positive pressure to open, how can negative pressure open the cap to pull it back in?!?

Sorry again for the questions, but you guys have been on here for ages and know your stuff!

 

That would have been some helpful info in the original post.

I would start inspecting and testing your caps and filler neck. Maybe the pressure release spring is getting caught or bound in the neck.

 

There's only one way the cooling system can be maintaining pressure from when the car was shut off hot, to when it's opened cold: there has to be a pretty large trapped air volume or a REALLY spongy hose in the system acting like an accumulator. You know all the ramifications of those, so I will not try to explain further.

 

Another thought - for the cooling system to have pressure cool, the air would have to be accumulated during running, and that seems to me to indicate a possible coolant seal problem.

Dave

 

I'm thinking the failing water pump is the culprit. I've noticed it whining a bit at idle, and the pulley has some free play. It also has been weeping coolant.

I'd be very surprised if it was an internal coolant o-ring problem, as the engine was assembled with the utmost care with new seals and I've never had a problem like that yet with any builds.

In the process of swapping in a new one right now

 

I guess the WP could be sucking in air if it's leaking, and causing the system to pressurize...


Dave

 

thanks for all the input guys, this seems like such a simple problem but certainly nothing I've run across. It's odd b/c the water pump has maybe 5k use on it but it's definitely failing.

 

i will mention taking another lookback at the overflow tank and lines when i got mine and was doing the rebuild i checked the tank cant remember why but it had an interesting chunky stuff inside and the lines were clogged. took me a bit to clean it all out but this might be the issue did you blow air through the line or just check for kinks? how bout the tank? seems possible maintaining pressure like that.

on that note my romate found a certain batch of the peston coolant cant remember was recalled i believe the 50/50 it was a big thing on the supra forums. basically the growth inhibitors werent mixed right or balanced somehin or other and it grew this wierd muddy crap smelled like s*** in anycase take a look see.

in fact hes still running it cause its not causeing issues lol stupid JZ sereis engines i swear you have to be a complete idiot to be able to blow those up

z

 

Rich, hopefully your water pump just got jealous at all the attention the rest of the motor got! I can't remember, but did you send the pump off for Coating? If so, could that have had something to do with it you think?

 

Ihor also suspected it might be the water pump and he was correct.

Upon removal, the pump made squeaking noise when turned by hand. It had been polished, whether that had anything to do with an early failure is TBD.

The car runs the same as before wrt coolant temps, but now I can let her cool off and remove the filler cap with zero mess

Hopefully people searching in the future find this thread useful. Just goes to show one can always learn more about these cars, just when you think you've seen it all they throw you a curveball

 

yeesh, hope it wasn't one of the re-medy pumps $$.

 

Interesting! Nice that it was just the WP.

Dave

 

Rich, if by polishing you meant it was tumbled in an abrasive media, then possibly the media entered the weep hole and destroyed the seal.

Barry

 

edit

 

Rich,

I'm not sure when you are opening your cap (temp), but your coolant system is suppose to hold 1.3bar of pressure and suppose to open when its above that point. It could be possible that your system is still holding this pressure when you are opening the cap.. especially if the engine is not completely cooled. Also, what percentage coolant to water are you running.. Or are you running Evans?? That could have something to do with it as I believe temp/volume is different.. ie, Evan's volume changes very little... or more coolant percentage volume will change less vs. more water.

Also, I'm not sure if pressurized system could be blamed for WP.. If the WP is leaking (which is what I consider bad pump), your pressure will be zero because the system will try to release pressure to the leaking area...

 

Seals can be wierd animals. A WP seal can leak one way (from out to in), sucking air in (the WP creates a low-pressure area near the shaft to draw coolant in from the radiator - and can cavitate, indicating very low pressure, maybe below atmospheric), since it is designed to hold pressure inside. Also, it could be leaking only sporadically, and be able to hold pressure when the engine is off. Some of this logic is empirical, since the air had to enter the system somehow.

One cannot, however, disregard a malfunction in the overflow system, which might block coolant from being drawn back, pulling air into the engine thru a weak WP seal. However, this does not totally explain retained pressure when cold.

 

Dave,

I agree that water pump could leak in both directions.. But usually opposite direction when coolant system pressure hasn't build up, ie when engine is still fairly cool.

I also was going to state that Rich's issue could of been the cap to the reserve tank where the line could of kinked and couldn't release pressure even when the cap opened up at 1.3 or 0.9 bar... as line isn't letting the pressure out. But I think the likelihood is the fact that engine still was holding 1.3 or 0.9 when rich opened the cap.

Either way, glad you got it all working properly now.

 

This is my best guess also. I had mentioned earlier in the thread that I had checked the coolant lines and there were no kinks. The failing water pump was sucking air into the system through the weep hole....it looks like it started to leak a bit (the residue was there) and then had stopped leaking, instead it was sucking air in. I'm just happy that the cooling system is back in top-notch condition

 

Glad to hear you got that figured out. Do you think the failure of your WP has anything to do with belt tension? I think my WP is going to die too (play in pulley), and I may have overtightened the belt a bit too much (I had an idler pulley installed instead of air pump)...