Vexing Problem

[Falcon148]

Problem, Car overheats after about 275 miles at freeway speeds, due to coolant being pushed out through the overflow bottle; I do see bubbles in the overflow bottle. Oil is not milky or shows any signs of having water in it.

Car History, 1991 Supra Turbo, bought new in early 1992. Blew head gasket at 71,000 miles.
Had the head resurfaced and lapped to an RA of 12. HKS head gasket and ARP head bolts torqued to 75 foot pounds, also did the full Lexus mod at this time.

Car now has 408,852 miles on it with only having to do normal maint on it.
Car has all it shrouds.

What I’ve done so far.
Replaced fan clutch, replaced thermostat, removed and checked water pump, tested then replaced the radiator. Tested coolant with NAPA block testing kit several times under different conditions, (used almost the whole bottle of fluid) all test were negative.
There are no exhaust gasses in the cooling system.
I didn’t want to pull the head but finally broke down and did it. I could find no signs of a blown head gasket. Had the head check at the same time, head is still straight.

Could the turbo be pumping air into the cooling system??

 

[GrimJack]

No, the turbo cannot do that.

A faulty radiator cap could cause that. Did you replace or pressure test the cap?

 

[Falcon148]

New cap and radiator.

 

[AJ'S 88NA]

What kind of cap, Toyota or other?

 

[Another MkIII]

Off topic, but props for over 300,000 miles on a 7M with no rebuild. And who says a 7M can't be reliable.

As for your issue, I would double check the cap with a pressure tester, I've seen more than one new cap be bad out of the box. Actually, I've had two in a row be bad out of the box on my car.
-AM3

 

[GrimJack]

Also, can you describe the bubbles? Are they violent? How much coolant is being pushed out?

 

[Falcon148]

Cap is a Toyota cap, and it passed the pressure test.
Bubbles are not violent, just a steady stream of them, but it only happens if you push the car hard or try to cruise a long distance at high speeds (aprox 75 mph for 275 miles) before enough coolant gets pushed out to see movement on the temp gauge

 

[GrimJack]

Ambient temps in your area? Intact fan shroud? Under engine cover?

 

[A. Jay]

Off topic, but props for over 300,000 miles on a 7M with no rebuild. And who says a 7M can't be reliable.

As for your issue, I would double check the cap with a pressure tester, I've seen more than one new cap be bad out of the box. Actually, I've had two in a row be bad out of the box on my car.
-AM3

I was just gonna say the same.

Ambient temps in your area? Intact fan shroud? Under engine cover?

OP said "Car has all its shrouds".

OP: check to see if the hose in the overflow bottle is leaking/not on right. I'm searching for it now, but there was a thread recently that came to that conclusion.

 

[Turbo Habanero]

For a side note I live in Arizona (pretty hot area) and my car never over heated I also did not have a fan shroud or under cover I'm not sure if I'm lucky or what but I don't see a small crack in the shroud causing the car to over heat or a missing under cover

 

[Falcon148]

Ambient temps right now are between 60 to 85 degrees. As noted in my first post the car has all it's shroud and under engine cover.
A. Jay, I saw the same post about the crack at the top of the overflow bottle and went and check mine along with the hose going to the radiator right then

 

[Hotwheelsjr]

I have a similar problem, but haven't seen it actually "over" heat, yet. Around town driving my temp stays normal -- I have a fan controller set at 88*c (190*F, I have a 190* thermostat) and it some times doesn't even turn on the fans around town. On the freeway, it's a different story -- I've seen the temp rise to 110*c+ (230*F+) and it made me a bit nervous...but the factory gauge was "normal", slightly rising to H, just above center. Same deal...coolant being pushed into my overflow, but not very much and not enough to really affect the coolant level in the radiator. I attributed the high heat to having too much crap in front of my radiator -- 4" FMIC, oil cooler, AC condensor, and THEN the aluminum radiator with twin 1550cfm elec fans and shroud. I don't think I am getting enough air flow to keep it cool at highway speeds/rpm. I figure at town speeds/rpm the air flow is sufficient because the motor is not being worked at 3K+ rpms. Sound about right?

 

[OfnaRcR4]

I had a van that did this. Rad was full of that sealer stuff and it hindered flow so the car would overheat. Got it unclogged and it fixed it.

 

[Falcon148]

Hotwheelsjr, I have always shut the car down before the temp gets a bit more than halfway, so it has never really overheated, don't want to warp the head now do we. Also this car is still stock as far as the cooling system goes and if I am remembering my figures right the stock setup pulls more air than most elec fans do.

OfnaRcR4, The radiator is new, and I flushed the system when it was installed.

 

[Hotwheelsjr]

Hotwheelsjr, I have always shut the car down before the temp gets a bit more than halfway, so it has never really overheated, don't want to warp the head now do we. Also this car is still stock as far as the cooling system goes and if I am remembering my figures right the stock setup pulls more air than most elec fans do.

OfnaRcR4, The radiator is new, and I flushed the system when it was installed.

Ya -- the after market elec fans I have pretty much suck. My buddy and I are going to fab a later model elec fan from a Caddy that pulls air like a mother. We'll see what that does for me. Def not happy with the fans I have...

 

[Falcon148]

Go back and do a search on the forum, these guys have tried just about every fan you can think of. From what I can remember the ones that worked the best came off of a Ford, I can't remember which model

 

[SPOOLINLUST]

Have you flushed/changed your coolant? If it breaks down it will leave silicate deposites and look like a piece of a rubber glove when found stuck in a t stat neck.

 

[Falcon148]

Spoolinlust, the cooling system has been flushed, and the thermostat is new from Totoya. Before anyone ask the jiggle valve is in the 12 o'clock position.

 

[3p141592654]

With the car hot, is the upper rad hose firm. If you squeeze it do you hear/see coolant movement in the overflow bottle?

 

[satx88supra]

Air in cooling system??