Vexing Problem

[Falcon148]

Satx88supra, air in the cooling is the whole problem, somehow, someway, pressurized air is getting into the cooling system. I have ruled out a blown head gasket, both by using a block test kit, and then because all the problems pointed to a BHG I pulled the head but could find no signs of a BHG whatsoever.
I thought that maybe the waterjacket in the turbo had a very small crack in it and pressurized air was getting in that way, but GrimJack said that it can't happen.

 

[SPOOLINLUST]

Wounder a bad throttle body can cause this? I believe it has coolant passages in it if one is leaking into your intake. How did the plugs look?

 

[Falcon148]

Spoolinlust, that is a great idea!!! I was thinking in terms of a source of pressurized air and all I could think of was the compression from the cylinders and the turbocharger. I had forgotten that the throttle body is also water cooled. Plugs were a grayish-tan color just like they should be. It will be the weekend after next before I can pull the throttle body as I'm on call this weekend and just don't have the time to do it.

 

[GrimJack]

How much boost are you running? Most cooling systems have more pressure than the intake...

Also, I hate to say it, but the stock temp gauge isn't very accurate except at the bottom and the top. Everything in the middle, well, I could guess a number with better accuracy.

 

[SPOOLINLUST]

How much boost are you running? Most cooling systems have more pressure than the intake...

Also, I hate to say it, but the stock temp gauge isn't very accurate except at the bottom and the top. Everything in the middle, well, I could guess a number with better accuracy.

Another affirming point of the temp gauge. Thank you. Well let me know what you find, also doesnt the EGR cooler run into the intake as well? Its been 2 years since I had mine apart cant remember or look at mine cause I blocked it off lol. Good luck man hope it solves the problem!

 

[Falcon148]

LOL, GrimJack, I am aware of the reputation of the stock temp gauge. I'm running between 14 and 15 pounds of boost and thats right at what the water pressure should be in the cooling system when its hot.

 

[3p141592654]

275 miles would be ~3-4hour of driving, 99.99% of which would be with no boost I would guess. Are you saying that for the first ~3 hours all is well, no bubbles etc. and then it suddenly overheats after that?

The stock temp gauge is designed not to move over normal operating conditions (keeps ignorant customers happy, avoiding needless warranty work). I characterized it here if you want to see how it responds. The stock gauge actually goes down (!!!) from 221 to 234 degF, then it shoots up fast hitting 100% on the scale at 248 degF.

http://www.supramania.com/forums/showthread.php?47479-Temp-Gauge-Calibration

 

[Falcon148]

3p141592654, I looked back over my old posts and I could see where you would think that. To Clarify, if I drive without getting into the turbo you will never get any bubble in the overflow bottle. If I drive it hard or get up to interstate speeds (75mph) you start to see bubbles in the bottle, after aprox 275 miles enough coolent has been pushed out of the system to start showing up on the temp guage. Also where I live is very hilly, so on the interstate your in and out of the turbo all the time.
Now, I'm a field engineer and my job requires me to driver alot, aprox 300 to 400 miles per day so you can see that I'm having to add coolent to it about twice a day.

 

[3p141592654]

Then I would suspect a crack in the head, that only shows up under high cylinder stress.

 

[GrimJack]

Then I would suspect a crack in the head, that only shows up under high cylinder stress.

I would agree... or some other leak that only appears under stress.

I've seen the block test pass in such conditions.

 

[Falcon148]

How would you find such a crack?? I have already pulled the head once and had the guys over at Top Speed Preformance look it over and they could not find anything wrong with it.

 

[3p141592654]

The block has been known to crack between the bolt holes and coolant/oil passages

For the head, you should use a dye penetrant process like the one described here. Hopefully this is what TSP did for you when the head was off.

http://www.youtube.com/watch?v=npgoUHq3X4k

 

[onemancrew]

Im suprised noone has mentioned the heater core yet... Same thing happened to me, i had to replace my heater core last week. One tiny crack in it will make it suck in air.

It may or may not be that noticable on the carpets inside. I have replaced a few of them now and sometimes its not obviously leaking. Get a torch and have a really good look up under your dash, chances are you will see some coolant dripping from the joins in the vents.

 

[Hotwheelsjr]

I just saw in the "what did you do to your supra today" thread about someone mounting their oil cooler in front of the radiator and it was mentioned not a good idea because of the heat the oil cooler generates. That might be half MY problem! I have my oil cooler mounted to my condensor which in turn means the radiator fans are sucking hot air caused by the hot ass oil cooler. I know for a fact my oil gets in the 150 - 200* range fairly quickly and stays in that general area. So, instead of the fans pulling 80-90* air through the radiator, a section of the radiator is pulling 150+ degree air. Hmmmmmm...now I have to think about relocating my damn oil cooler. Granted, it's a stock cooler, but it's still generating heat right in front of the radiator!

 

[onemancrew]

I just saw in the "what did you do to your supra today" thread about someone mounting their oil cooler in front of the radiator and it was mentioned not a good idea because of the heat the oil cooler generates. That might be half MY problem! I have my oil cooler mounted to my condensor which in turn means the radiator fans are sucking hot air caused by the hot ass oil cooler. I know for a fact my oil gets in the 150 - 200* range fairly quickly and stays in that general area. So, instead of the fans pulling 80-90* air through the radiator, a section of the radiator is pulling 150+ degree air. Hmmmmmm...now I have to think about relocating my damn oil cooler. Granted, it's a stock cooler, but it's still generating heat right in front of the radiator!

Nup, i dont think so, Ive had my oil cooler directly in front of my Radiator for years now and no problem at all. Check for tiny leaks,,, heater core especially.

 

[Hotwheelsjr]

Thanks -- I think I licked it today. The crap fans that came with my radiator were just that...crap. I replaced them today with a set of fans that were on the car I pulled this motor out of. They're not Toyota, but they fit my shroud mounts perfect and they pull about twice as much air as the POS ebay crap I took out. Ran around most of the afternoon in 95* Arizona weather and my temp never went above 190* -- the temp rating on my thermostat.

 

[SPOOLINLUST]

Sounds good! well hope it doesn't return, reading other post's the stock fan and shroud is very adequate. Also ebay crap like you said is just that lol

 

[Hotwheelsjr]

Just finished posting this in the "what did you do to your supra today?" thread...

Almost took a 5gal can of gas and a match to mine today. Couple of days ago I felt I had licked it's cooling issues. Took it for an extended drive today and temps were great even in 100* temps this afternoon in AZ. My son heads out with it this evening and calls me down from my bedroom about 30 mins later...says it's spewing coolant. We pop the hood and coolant had sprayed ALL over my once clean engine bay. The f'n L shaped hose under the water neck/thermostat housing blew a hole and pretty much emptied my coolant system into the electric fans which in turn blew it all over my fn motor. Sumbitch...

I can't win for losing...

 

[3p141592654]

That hose often fails when the factory heat shields are removed or broken, especially the little L-shaped metal tab between the ex manifold and the hose.

 

[SPOOLINLUST]

Well my friend I can say I know EXACTLY how you feel, same hose got me but driving down the road luckily just before I got to the shop it was going to. Not to mention I forgot to tighten the clamp on the spout that comes out of the rear of the head. Well hopefully that's all that it is.