4AC AE92 Overheating, but head gasket is fine?

[beerhead]

Well the sender is on the radiator side, so if the thermostat is clogged, its not getting flow.

No no...

The temp sender is on the HOT side of the thermostat, not the cold side......

top hose gets hot (feed), bottom hose stays reasonably cool (return).

[beerhead]

I should add 4A's are a bit odd, normally a thermostat is on the output of a motor, but on them there on the inlet, so when the thermostat is closed the only water that's going through the motor is going through the 18mm tube from the outlet of the head, that's already preheated.

[stradlater]

Beerhead - The temperature sensor your referring to, is the thermofan sensor trigger.... Which, I might add, seems to work appropriately.

However, the temperature GAUGE sensor, is only the engine side of the thermostat, thus negating what you are referring to.

As for oil in water, or water in oil, the engine shows no signs of either. I'm going to rip the thermostat out and run it without and see what happens.

What is this bypass hose people talk about?

And yes, I got the feeling the hoses are arse about on the 4a's..... Didn't seem to make sense!

[stradlater]

Oh, and 150psi per cylinder seems right to me, my wrecker purchased 1uz only had 160psi per cylinder.

The reading on the 4a was incredibly consistent - 150psi on the dot, for EVERY cylinder. I was amazed considering it had 300k's on the clock.

[litldv8]

the bypass hose is the smaller hose out of the back of this housing me thinks you will find
and thanks for the pic beerhead

[JP]

If you've never had the radiator serviced properly, I'd take it to a radiator shop to have a tank removed and rods used to unblock the core. I'd bet the core is at least 60% blocked from my experience with A92's. Costs me $80 per radiator to have them cleared at my local radiator place.

[dangdang]

Oh, and 150psi per cylinder seems right to me, my wrecker purchased 1uz only had 160psi per cylinder.

The reading on the 4a was incredibly consistent - 150psi on the dot, for EVERY cylinder. I was amazed considering it had 300k's on the clock.

Good little engines, I tested my early Bigport 4age last week and it measured 145psi with not even 1psi variance between cylinders, the other guys in my workshop blew out! And with 275 thousand and a cracked block mind, I get it bloody hot all the time and it just wont die

[beerhead]

lols, wrong sensor, but I still think the thermostat is why its overheating and the gauge isn't reading true. Unless the gauge sender is had it, the only way for it not to be showing the operating temperature of the motor is if the water isn't flowing through the cooling system properly.

If the thermostat is open and the radiator is blocked and not running efficiently you'd see the gauge reflect the overheated engine temp.

lol in the time that took to write I would have had the thermostat out and taken the car for a test drive already

[BLK_20v]

If you've never had the radiator serviced properly, I'd take it to a radiator shop to have a tank removed and rods used to unblock the core. I'd bet the core is at least 60% blocked from my experience with A92's. Costs me $80 per radiator to have them cleared at my local radiator place.

For not too much more you can buy a brand new one....

[stradlater]

The problem with removing the thermostat on this motor is the fact that the thermostat IS the seal.

Once you take it out, you only have a small rim of metal with which to place some gasket goo, and then have to wait for it to cure, then fill and drive the car.

It's not small feat just to test if it's the thermostat. This is why I'm not rushing to do it.

I would be too that the radiator is partially blocked as was said. Thing that bugs me is that I dont' know whether that's the thing causing the issue. I need the issue fixed first, and then I'll go about fixing the rest of the problem.

Anyone still placing bets on the water pump? or is that out of the game do we think?

[JP]

The thermostat is sealed by a rubber gasket that clips around the edge of the thermostat, cost about $2 from toyota. perfectly reusable if it's not 20 years old

Edit, just re-read the posts above and realised it's being recommended to remove the thermostat... That will make the engine run hotter, the thermostat is needed in the system to slow the coolant down and let it pull heat from the engine. If you're going to bother draining the coolant to check the thermostat, I'd put a new one in at the same time, last one I bought was $17 for a geniune part from toyota.

[stradlater]

Yeah, I think I might just replace the thing for peace of mind, however it actually looks in good nick though. :-( Damn thing.

[matty12]

when the fans on is there hot air blowing out??

Feel across the core and see if it has any cold spots.

[2jzhilux]

A compression test is not a 100 percent acurate way to tell if you have a head or headgasket problem.
You need to do a cylinder leakage test and a TK test.
The compression can be ok and you can still have a cracked head or stuffed gasket.
Basically put the cylinder so the valves are closed and it is on tdc and then pressurise the cylinder with compressed air the check the cooling system for bubbles.

[stradlater]

2JZ - Thankyou mate. I think you may have helped identify the problem.

I spoke to my radiator man this morning and he said that it sounds like a head gasket too.

One of the important parts is: With the radiator cap OFF, even at cool temperatures I see whisps of gases coming out of the radiator cap. Kinda like steam, but not as hot, and not a voluminous. It floats out of the radiator cap.

The man said it's probably exhaust - and I tend to agree now thinking about it.

What would you think?