Supra Overheating - Need help

[Kagetsu]

My Supra is overheating. Basically will drive along for a little bit, and then starts to overheat.
My initial suspect was the thermostat failing. Originally I tested this a little, that when I start the car up, and it reaches operating temperature, so long as I keep it above 2000rpm it runs okay, then below that (or there about's)the flow stops regardless of revs. originally, I suspected the thermostat, which I cut the centre out, but the problem still occured.

So my new suspect is the water pump (driven by the serpentine/fan belt). My question is, does it have a clutch, or would it likely have other issues?

[Mr Ed]

Water pump should makes noises and leak before it actually stops working. Dont think it has a clutch so it should be on constantly.

Flush radiator with special radiator cleaning stuff and try again maybe??

[Kagetsu]

Kind of like a rattling noise? Also does appear it 'may' be leaking.

[legend]

i would get the radiator reco toyota use fine tubes which block easily give it a radiator flush ,reco it and new coolant
other than that it could be water pump,running lean, or to far advanced ,slipping belt
radiator reco is cheap insurance and its summer here come those 40c days

[Kagetsu]

No point before new engine. Will be going full aftermarket, but will wait for motor to go in at the same time to make sure it all works together. Nothing's blocking radiator.

Car cools fine for a while, then it's like the thermostat (which is no longer there) just shuts, and nothing, the car quickly over heats.

I forgot to mention, that I noticed the problem and immidiately thought Thermostat, so I did a full system flush, and changed the fluid, before I cut the thermostat.... Tried the thermostat and refreshed the coolant, and now basically there at the water pump. The radiator flows fine, nothing stuck in it.

[Vios-GT_07]

wait.. is this the supra with a 7M in it??

check for BHG... before u do anything else..

and yea the waterpump is a very simple devide.. it's basically a straight driven turbine that moves water with movement from the belt... no reason it should faul unless the bearings in it have gone, in which case it'd leak, rattle, or seize completely (and shread your belts)..

[Kagetsu]

Sorry mate, 1997 SZ-R. NA 2JZ....

Not a blown head gasket. ^_~

[Shaddow]

When you say you cut the thermostat, did you actually remove it from the cooling system? That bits confusing.

You've done the usual checks for a blown head gasket like bubling in the radiator, oil residue in the radiator, milky substance in the oil?

Are all the pipes pressurising? Just as it reaches normal temp, make sure all the water pipes have pressure in them and they are hot. Good sign of whether water is flowing.

Are you getting a water loss? Also with the thermos wire them to run on ignition not temp if you just want to keep driving till you find the problem.

And lasty is the car running lean? I know it sounds silly but if the cooling system is a bit sad a lean engine can cause a car to run hot. Mostly only ever see this problem on carbied cars though.

[Kagetsu]

NA's don't have thermo's, in favour of the clutch fan. All pipes are preasurised. I've checked all the stuff indicating possibility of head gasket, and it's not that.

Let me describe it again.

Water simply stops flowing, but system is still under pressure, water bubbles from the overflow. There's the possibility of water coming out of the water pump, but it's not very noticeable. This occurs AFTER the car has run NORMALLY, even opperating at normal tepmerature for several minutes... I don't make an effort to drive a car that's got issues a lot up here.
Problem occurs exactly when revs drop down, not before.

By cutting the thermostat, I've removed the valve by sawing it out. Sill has the same restrictions as before.

Nothing wrong with anything else.

[Vios-GT_07]

hm...

that's strange... sounds to me like ur water pump has seized.. or it's not spinning under 2000 rpms...

what i suggest is, when car is cold, start her up.. with the cap open.. and u should see the water run... after it warms up and idle has come down, and water isn't running, ur water pump is fucked (though i must say i've never seen it fuck up like that b4)

just to be sure i get this correctly, at the operating temperature.. the water moves only above 2000 rpms.. and anything below u'd overheat?

then yea.. waterpump is suspect...

[Shaddow]

Fair enough. Does sound like the pump. I'm not familuar with the engine (is that obvious yet ) but is there any problems with the belt? Slipage? If the pump is trying to seize? Have you taken the pump off at all? Might be time to do if nothing else presents itselt. Even try taking the belt off and see if you can spin it easily by hand. There's always a chance the vanes have eaten themselves out and under 2000 its not moveing enough water for you. Unlikely given the age of your car.

After that I'm stuffed if I know.

P.S. I hate clutch fans. I drive old cars like 30yrs mostly cause thats what I like and the clutch fans are always siezed or just noise designs. Much prefer thermos for lack of constent noise and the added lack of sucking HP all the time. Hey in my low HP powered cars everything counts. Good luck

[Kagetsu]

Cheers guys. Every bit helps. ^_^

[AndyTTR]

The water pump on my mates JZA80 2JZ-GE rattles too, i think its the fan clutch. Must just be something that they all do.

So you're saying it overheats when the revs drop (meaning the ecu has detected that its at running temp). That doesn't mean that it's only overheating from that point on, it could mean that there's no cooling happening at all. Ie. the temp just keeps going up after reaching operating temp.

Maybe try putting a new thermostat in it? I haven't seen how the 2JZ works, but on the 3S the thermostat also controls the flow through the bypass pipes. If you run it without the whole thermostat the coolant bypasses the radiator completely and overheats the engine.

If you've looked at all the other possibilities, maybe its a cracked head? That's what caused my old engine to constantly overheat and die.

edit: was also going to suggest checking the serpentine belt for tension / slippage. Have you checked if the pump is turning at all?

[Kagetsu]

There's no bypass pipes for the thermostat in the Supra. Radiator straight to the Thermostat.

Will check the pump for slippage tonight.

[EldarO]

if your car runs hot, and you rev it, then the temperature drops, it means its low on coolant, as the pump, when you rev it, pushes the water through the head, and it needs the extra revs to do so when its low.

Eldar.O.