Overheating '93 V6

Off the top of my head... has the thermostat been replaced recently?

When's the last time the water pump was replaced? (How many miles has the car been driven again?)

Could be a leaking head gasket, letting gas into the water jacket making it hot. A restriction might cause the top hose to collapse (does it feel hard?) - that might be thermostat or perhaps a buildup of leak stopper... which might have blocked up the radiator. I had that once, cooling system was half empty but a restriction made it look full. Then it's hard to tell if the problem began with a leak or the head gasket failure. Not cheap to fix but the car seems fine after 12 months so it was probably worth it.

Start with a new thermostat, but use a Toyota, ive has a few bad aftermarket ones. Check the lb rating on the pressure cap to be sure they put the right one in, any garage can tests its pressure release to be sure its good. Do you fill the expansion tank to the line marked on it, if you just fill it to the top it will overflow. You do run a 50% antifreeze mix, right.

You should be able to tell a head gasket leak by the oil looking milky

That's only one of the possible symptoms, so are; coolant overflowing, bubbles in the coolant, oil in the coolant and overheating for no apparent reason. Not wishing it on giblet, but I have had very similar experiences. Trying shortcuts to stop leaks has been a big mistake twice for me.

No, I think it is the original

The water pump was replaced about 5,000 miles ago by the same guy who can't solve my problem now. He said he had spotted a leak. When he chacked it after the overheat, he said it looked fine, no problem.

===================== First of all, insist the mechanic use genuine Toyota parts and replace the thermostat and radiator cap. If the problem is still there, then write back. If you look at the Toyota radiator cap, it fits a small filler neck, and has several moving pieces to allow coolant to be drawn back in from the recovery bottle. The actual opening in the filler neck isn't much more than half an inch, so an aftermarket cap could be one source of the problem. Here's another tip, though it might not make much difference. There's a "jiggle valve" in the new thermostat, and it should be aligned with the cast in mark on the inlet pipe, near "12 o'clock" position. Also, make sure he knows the new gasket wraps around the edge of the thermostat, but that should be obvious. Also make sure the thermostat is not installed backwards. The printing indicating the opening temperature and the short tapered part of the thermostat faces out.

This has the classic symptom of a blown head gasket. Prolonged highway driving is usually the only thing that puts enough stress on the cooling symptom to have it overheat with a gasket issue. Happened to my wife's '93 camry exactly the same. Go get yourself a chemical block tester kit for $25 and check for exhaust gases in the coolant. If positive, then get a leakdown tester or somethng similar and test each cylinder with pressurized air and slowly hand turn the engine crankshaft from the wheel well while observing the coolant reservoir. When you see bubbles, you have found your leak.

dave mc

Agreed, likely a blown head gasket.

But the rad cap is probably bad as well. Make sure you get one with a metal spring-loaded vacuum return valve ($8 at Kragens), not one with the hanging plastic valve like the one Toyota likes to sell. It should have allowed coolant back without causing the top hose to collapse.

The major issue first is finding out if the gasket is blown. If so, I'd use only Fel-Pro's multi-layer steel (MLS) head gasket on that engine.

davemac wrote:

The wrong cap could have blown the head gasket if that is the case, but a bad thermostat not opening fully might be the cause of everything, you realy need a complete go over and a real mechanic, not your Hack.

You are correct. If the gasket is gone, it is wise to overhaul the whole cooling system and replace the thermostat, hoses, rad cap, water pump, flush it very well, etc. I would also carefully check the rad for any cracks. In my wife's case, her plastic OEM rad had developed a crack in the top and she was losing fluid and running hot probably for quite a while which I think may have caused the gasket to blow. But then again, it could have been the other way around too since the hot exhaust gases in the coolant would have put some considerable strain on the rad.

dave mc

Hi everybody

I am extremely grateful for all the responses, and I have a much better understanding of what might be going on and what to do about it.

I am no mechanic and this is my 6th Toyota and I've never had any trouble before. As long as they are serviced properly, they just seem to keep rolling. I think I was also very lucky with the mechanic I used to use without knowing it. We moved house by 200 miles a couple of years ago and the local guy I have been using since then has turned out to be a real dumbkopf.

Anyway I decided to get my cooling system completely checked and overhauled, based on the advice you've all given, and started asking around for a good cooling system mechanic. I got the name of the same name from more than one source...he seems to have a rep for expertise and thoroughness. Problem is he is about 10 miles away in the wrong direction...but I'm sure it will be worth it. I will post back on the board to let you all know how I get on.

I am so impressed that you have all taken the time to help. Many thanks.

I broke the top neck off my 91 radiator leaning on it lightly while removing the oil filter. It was like varnished cardboard.

I once read some radiator company's web site mentioned the design life for the brass rad is less than an aluminum-plastic rad. The design life was somethin like 120K-150K miles. Can't remember where at the moment. But wouldn't be surprised if a rad falls apart from old age, even with regular coolant change.

jg wrote:

It had a fair life, but if it had fallen off along the road (which it would have) it would let it all out in one go. Copper radiators usually develop a leak and give you some warning before doing big damage.

What ruins the radiator is having it low on anti freese. The steam that is created will distroy a plastic type rad in short order

I'm finding it harder to like plastic radiators all the time.