Ideas please - Slow overheating issue - 2JZGTE

[sbyder]

After some spirited driving, or an extended period of traffic driving, water temp will increase slowly to 102-105degrees before I turn her off and water will start dripping from the overflow bottle. If i drive sedately and in constant movement, i havent seen it pass 90°.


This started happening a few months ago after a spirited drive and I still havent worked out the problem.

New items:

Alloy radiator.
Radiator Cap.
Waterpump.
Thermostat (even tried a low temp thermostat which works better, but still has the same overheating result).
Supra Engine fan with new silicon fluid, locking up perfectly.
Rear engine to front engine coolant line connection.


Pressure test showed no leaks.
Most rubber coolant hoses have been replaced and have proper hose clamps.
No water in oil or oil in water.
No water out the exhaust and no lose of coolant (until it comes out the overflow).
Radiator system has been bleed properly, so no air locks.

If water temp gets to 98° at idle, I increase RPM to 3000rpm momentarily and the engine fan will cool it back down to 92°, but then once back at idle it will slowly increase to 100° and would keep climbing but i turn the engine off.

I am starting the think its a headgasket, or a cracked head, but there is no obvious signs of either apart from the overheating. Apart from a dye test, is there anything else i can try to test the theory? Dye test is booked in for wednesday but I would like any other suggestions people have.

Ben

[ra65]

edit - already done it.

[Kyosho]

Have you flushed your cooling system out properly?

You may have blocked passages etc not allowing it to cool properly.

[sbyder]

yeah flushed the engine about 5 times now. Coolant is becoming part of the monthly budget

[wa5]

is the radiator cap the correct preasure?

are you SURE that the fan clutch opperates correctly. and do you have an old one that could be "tech screw" solidified? in order to check if the supra one is in fact working correctly. and does the car still overheat when idleing with the A/C (and thus it's electric fan) going?

This front to rear coolant hose, is it a standard thing or a recomended fix? (if the latter,, recomended by who?) are you SURE that the cooling system has been totally bled.? and is this related to the above bypass pipe?

your thermostat perhaps the opening temperature is too low?

is this motor fitted into a standard body (supra, chaser etc) or shoehorned into a mini!?

[fixeruperer]

do a tk test (co2 tester) see if it has a started blown headgasket.

[sbyder]

is the radiator cap the correct preasure?

Yes

are you SURE that the fan clutch opperates correctly. and do you have an old one that could be "tech screw" solidified? in order to check if the supra one is in fact working correctly. and does the car still overheat when idleing with the A/C (and thus it's electric fan) going?

Yes, clutch fan is pushing enormous amounts of CFM, its actually got new silicon in it. Aristo's dont have an electric fan, but I have a 16inch thermo attached as well.

This front to rear coolant hose, is it a standard thing or a recomended fix? (if the latter,, recomended by who?) are you SURE that the cooling system has been totally bled.? and is this related to the above bypass pipe?

The bypass system just makes sure the top of the engine see's the same temperature coolant. Some people attached it to the top radiator hose. The system has been bled many times and even so, all airpockets should have got out by now, 3 months its been happening.

your thermostat perhaps the opening temperature is too low?

It was actually too high. Bottom of the radiator was still cold after the engine heated up, so the thermostat wasnt opening. Small holes have been drilled into the thermostat to ensure it opens. and please dont say thats the problem, because a brand new OEM thermostat will not open at all because the radiator is soo efficient.

is this motor fitted into a standard body (supra, chaser etc) or shoehorned into a mini!?

Its the OEM motor fitted to an Aristo.

Thanks for all the hints/tips. Keep them coming

Ben

[MR 1JZ]

ben...have you got the thermo fan fitted to the front of the radiator???

i.e. is it blowing air at the motor?

[JustCallMeOrlando]

What size intercooler do you have?

[Kyosho]

It also sounds a bit like the water pump isn't pumping enough water...
If it cools down when revs rise (IE more water being pumped)
Try removing the thermostat all together.

[sbyder]

i have the 1J soarer/2J supra engine fan sucking through the radiator and a 16" thermo pushing air into the radiator.

The intercooler cant be the cause as it was cooling fine from Feb till August.

I agree with you Kyosho, it does sound like a waterpump. Last time i had the thermostat out I had a good look at the impeller with a funky camera thing ive got and the blades are all intact and rotate true and proper.

If the dye test doesnt show any signs of fuel in the coolant, then I will be removing the thermostat. If that fails, Ive got a stock supra radiator spare that i might throw in as well.

Cheers
Ben

[rms]

The bypass system just makes sure the top of the engine see's the same temperature coolant. Some people attached it to the top radiator hose. The system has been bled many times and even so, all airpockets should have got out by now, 3 months its been happening.

Ben

You didn't answer the question - is the bypass standard ? If it is not standard remove it.

Seems like you are recirculating coolant back to the suction side of the pump, it is not getting to the radiator.

From spec sheet

"coolant temperature is controlled at the inlet side of the pump by an integral wax element thermostat. the thermostat modulates coolant flow between a bypass line and coolant coming from the bottom tank of the radiator. when the engine is cold, the thermostat blocks the passage from the bottom tank and coolant circulates in a loop through the engine and bypass line only; it does not circulate through the radiator."

[amichie]

Sometimes the stock radiator cap doesn't seat prpoerly on aftermarket radiators.

Make sure you can feel the spring pressure as you fit/screw it on

[sbyder]

the bypass mod was done in an attempt to gain more control of the engine temp overall by providing the rear of the engine with the same coolant as the front of the engine. It was done in a last ditch effort to find the cause and it has done neither fix or cause it more problems. I completely understand what you're saying, but the way we've done it would make no difference to the thermostat regulation.

Thanks amichie, i have an aftermarket cap as the stock one didnt fit at all.

cheers again, keep them coming.
Ben

PS - dont think im knocking your ideas down, im just showing that ive already tested the theory's.

[wa5]

is the 16" thermo shrouded . I recently saw a buggy with a thermo fan mounted on a solid steel plate that sat less than an inch from the rear of the radiator.

How does the efficiency of the radiator effect the thermostat? doesnt it operate on engine temperature? IE the spring (opener thermostat thingy..... pardon the techical jargon ) it on the engine side not the radiator side? its not upside down is it?