well i didn't want read all of it but i read most.

first i would say why the fuck did you take off the egr. if anything it will only contribute to your overheating, but shouldn't cause anthing excessive. i think you went a little overboard on pulling the head but i've been there so i understand. do you have a wb to watch a/f. if not change your fuel filter. if it gets too clogged it will cause you to run way lean which will make your car overheat. by the way happens over 2000rpm it would make sense since at idle it doesn't take much fuel...

 

well i didn't want read all of it but i read most.

first i would say why the fuck did you take off the egr. if anything it will only contribute to your overheating, but shouldn't cause anthing excessive.

isn't egr part of the smog system "Catalyst"?

 

The only thing I can think of is a clogged hose somewhere, possibly.

Have you confirmed the temperatures are really bad or are you reading the stock gauge? You might have a bad temperature sensor

 

I didn't see it listed, but did you replace the main in/out rad hoses. At idle the hoses have very little pressure applied to them, but at higher RPMs, the pressure can collapse the hose restricting water flow, resulting in higher temps/possible over heating.

 

this is also a sign of a waterpump going bad.

 

Water pump.

Bearing feels great, seals fine, but the propeller is not tight enough on the shaft. During low rpm there is not enough drag on the propeller to slip it on the shaft, but at increased rpm the propeller will turn on the shaft, heating it up and making it slip worse. When engine goes back to idle, there is less drag on the impeller and it does not slip anymore allowing it to cool back down and temp goes back to normal.

Retarded guess? Maybe... But it is the only thing i can come up with other than:

Something blocking the coolant passages somewhere along the line. Increased water flow pushes a blockage onto an opening of a water passage. (frost plug maybe that has accidentally been bumped inside the block?)

 

Well I have checked the hoses (one of the first things I did), and they are both free of restrictions, and not only don't collapse, but are quite hard, indicating plenty of pressure there.

As far as the water pump being bad, there are several things telling me that is not the case. First, I get plenty of pressure, second you can see the radiator flowing quite well when you run it with the cap off, third I removed it from the engine, and examined it to see if it was the impeller slipping. I could not turn it by hand, so I clamped the pulley-end in a vise a used a 2-foot channel-locks on it, and turning it as hard as I could it would not budge, so I am quite certain that it is not slipping. Also I have a spare water pump that behaves the same way, so I pretty much ruled that one out, but it does overheat like that so it was one of my main suspects.


As far as restrictions: I first flushed the block with water from both heater hoses, then the radiator, then the water pump hole (after taking it out) and both the radiator hoses. After removing the engine from the car, I blew them out with compressed air. Also I looked in all the passages and hoses and holes I could see (coolant and oil) and there are NO restrictions I can detect. The water flowed quite well and NO debris came out whatsoever. The passages all look quite clean and free of scale/debris/rust to the eye from all points I can see.


As far as temps: yes I have not only the stock gauge, which works, but also an aftermarket gauge. I suspected this MAY have been the case earlier on, so I also confirmed these temps with an external multimeter with a temperature probe. Not only do all three gauges agree with the high temps, but upon opening the hood you can most certainly tell the difference from a 160* engine and a 230* engine, it feels MUCH hotter to the touch.

Like I said, all the normal things I have gone through and checked and re-checked and replaced and it is just not making any sense to me. I am at a total loss here as to why this is doing this to me. I'm very familiar with this engine, as I've done several motor swaps and rebuilds over the years and there is just nothing on here that looks bad or tests bad, but yet it continues to overheat for no apparent reason. There is obviously SOMETHING causing it, but WTF?!?!?!

Thanks to all suggestions thus far, please keep them coming.

 

If someone on here has a chance, can you test your AFM per the book and post the resistance readings for comparison??

 

what kind of headgasket are you using?

have you tried a leakdown test yet.. check all the frost plugs and make sure they are all snug and correctly seated.

check your radiator cap for the proper spring pressure to ensure it is operating properly, cap can cause it also.

when your running the car hard, turn on the heater when it starts to overheat and see if that helps the issue at all (not a permanant fix, but can give you an idea if its a clog or not somewhere else).

run a corrosion treatment through your coolant system, you may just have restricted passageways from previous corrosion, people like to put in normal water sometimes and fuck up the coolant passages... go figure right. and then run some dawn dish soap through it then flush it all out to make sure there sno weird oil buildup anywhere.

also try to grab a compression gas tester that goes on the rad cap... put the car on a dyno, throw that thing on it an run it real quick before it heats up wayy too much, and then boost the car (past 2k rpm like you said) under load, and see if the increased pressure is throwing small air bubbles into your system. if you get some small air bubbles from something in the system, itll cause th eoverheating, but even tually it will pass them through the rad through the cap also, so you may never see them.

run the car real hard, to the point of almost overheating, then stop, get out, and shut it off... lean really close to the head and listen for gurggles and sucking sounds.

try to get a stock toyota thermostat.. the aftermarket ones from checkers, are just cheap rebuilds, the toyota one is a fuckin piece of gold compared to those other ones.

if you took off the egr, ensure that the passages are properly blocked off and you didnt accidentally close off one of the passages to the 6th cylinder for coolant flow.

check your timing, your timing may be off at higher rpm causing an overheating problem and possibly more damage later

check for oil consistency and oil pump failure... your car may not be able to cool itself enough if your motor isnt being oiled sufficiently.

see if you can get ahold of some kind of thermo visual gun and see if you can find a hot spot on your engine as it heats up.... you may be able to find a culprit if you see an area that heats up abnormally fast also.



this is about all i can think of to say for righ tnow, ill check back in later, but hope you find it

GOOD LUCK!

Ian.

 

Whoa, good info all around!

I have pressure tested the cooling system, the cap is all good as is the thermostat. The freeze plugs are fine as well. Running the heater does bring the temps down a bit (maybe 10 degrees or so), but like you said not a permenant fix, plus running the heat all summer in Arizona may not be too good

As far as running it and listening, the only noises I hear are a sizzling sound coming from the turbo, which I suppose is normal lol.

Re the EGR, I only blocked off two places, niether of which was coolant, only air.

*
Timing wise, it is on at idle with the check-terminal jumped. It advances with RPM as it should, HOWEVER I do not know where it should be advanced to at ALL RPM's, only idle is listed.
*

I last changed my oil right before winter so it was getting dark. I just changed it now, so we'll see if that makes a difference but aside from oil pump failure, which I doubt I am experiencing, I've never heard of dirty oil overheating an engine but you never know with this damned thing. My pressure is as it has always been, about 10ish at idle and 30-40 driving, plus the motor makes no other signs of oil pump failure or bad sounding noises.


The motor is reassembled and back in the car, just have to finish hooking everything up tomorrow so we will find out whatall happens then. Thanks for all the ideas, I pray this works out!!!

 

...................Re the EGR, I only blocked off two places, niether of which was coolant, only air.................

There is really only one proper way to remove the EGR system. You need to remove the Cooler Plate from the back of the head and block it off at the exhaust port. If you leave the cooler plate on, you are just trapping hot air around the back of the number 6 cylinder without the EGR flowing. This is not good for a number of reasons, the number 6 is already the hottest cylinder. Some of those EBAY block off plates are misleading.

With Cooler Plate:

Without Cooler Plate:

The absolute best way to fill the cooling system is to buy one of these and mount one of the tees in an extended heater hose up above the rear of the head on the firewall, this will now be the highest point in the cooling system. Fill the system from here with the radiator cap removed and the engine idling. When it completely fills the radiator, put the cap on and finish filling until it fills all the way to this tee. No air will be in the system at all, period.

 

Another idea. Factory fuel pumps on this car has 2 relays, one for low rpm and one for high. IIRC it goes to high at the 2k mark. If the relay isn't kicking over then you may be running lean at that point. Also, what heat range are your plugs? I would lean more towrads the first idea.

 

Well I got the motor back together and in the car, and it still overheats like I didn't do anything to it. I am uber-pissed off.

I tested the fuel pressure of the pump only, engine off ignition on with jumper, and it is 40psi. Running with the vac. line to the FPR disconnected it is 39psi. Running with the vac line connected is 30psi. I also ran it up to 4k RPM with the gauge on, and it stayed at 40psi the whole time (FPR connected). This is the stock FPR by the way.


I tested my oxygen sensor, and the book calls for 3.0 to 3.6 ohms, and it reads 3.7-3.8 ohms. While this may just reflect extra resistance in the wires/connectors, it could technically be off. I was going to replace it until I see that they are ONE HUNDRED AND FIFTY FUCKING DOLLARS. Anyway, would it even make that much of a difference in A/F ratio to cause me to run lean? I don't think so, but I am really out of options for this thing to overheat now. I have literally done everything I can think of.

 

You might want to think about pulling the radiator and having a rad shop rod it out to check for a partially blocked core. If it is 1/2 to 2/3 blocked, it would look as if you are getting good coolant flow, but at freeway speeds there would not be enough to keep the engine cool.

 

10-4, gotta be that

 

after going through all this work why not just spring for a good aftermarket aluminum rad and see if that helps at all

 

The radiator is brand new out of the box 2 weeks ago. I was debating an aluminum one, but decided to just get the stock replacement.

The way it was acting SEEMED like a radiator blockage, or possible flow restriction of some sort. After replacing it, same overheating problem. I checked out the water pump. Fine. Flushed the block from both heater hoses, the main hoses, the radiator itself, and the water pump hole. All was fine, no crap came out, just water. After I removed the engine and examined the passages with a light, I could see there was no restriction. I also blew out EVERYTHING with the air compressor and flushed with water while out of the car. Again, flowed like a champ.

 

I can't imagine what else you can check, or do. Is there any chance at all that the lower radiator hose is collapsing on the inside (ply seperation) during higher engine revs? This would starve the engine of coolant. (I admit that is a very long shot, in 40 years of working on cars I have only seen that one time).

 

Brand new hoses

 

Assuming that you're GTE, what are the chances that the turbo could be causing this? CT's are bushing type bearing and can sometimes get gaulded, still spin but with lots of friction. Or maybe the journal in the bearing is clogged. Long shot but man you've checked everything.

 

Stock?
Mods list?
NA or Turbo?

* Exhaust leak (manifold), Exhaust timing, restricted exhaust (Turbo, Clogged Resonator, etc) ....Bad Head dunno: )

 

stupid question, how much crap has built up on the radiator (like physically on the outside)? I am going to assume your on stock intercooler.

did you keep the heat shields when you took the motor out? they help a lot with under hood cooling.

my gut instinct says replace that water pump as long as your there, just cause everything else has been tried. After that try the hoses as said, as your just running out of options and I know they may feel good but may be being deceptive, I know I have had that happen before.

good luck

<l><l>

 

Okay guru's, do your worst on this:

88 Turbo/auto, engine mods are: intake, 3" exhaust, boost controller, EGR removal

Brand new hoses. Brand new radiator. Stock intercooler.

My cam timing is on, as I just checked and realigned them when the head was off, intake and exhaust.

I disconnected the exhaust at the end of the downpipe to eliminate possible exhaust restriction, but I have 2.75" DP, no cat, and 3" cat-back so I doubt it is restricted anyway it made no difference.

Tried a different water pump, even though the one on the car appeared good in all ways, no difference.

As far as the turbo being suspect, I spun it by hand and it rotated freely. Minimal shaft play, fins not chipped. What else might make it bad?? It boosts okay, no whine of death, no abnormal sounds.

I have the heat shields for the turbo.

---------------------


It will idle perfectly fine, never overheating. As soon as I raise RPM's the temps just keep climbing. As soon as I return to idle, the temp will slowly come back to normal. This has to be the most confusing problem I've ever had, I've been at this for 2 weeks and checked or replaced pretty much everything there is.

 

what happens if you take the thermostat out?

 

Well I actually have not tried that. I didn't really think it was the answer. The t-stat works, and as such I should not have to remove it to prevent my car from overheating. It may serve to stop it from overheating by masking my problem, but something is still not working right. And at that, if it heats up that bad now, I believe it would only be a matter of a few extra minutes before it did overheat.

 

If I'm not mistaken the trans is cooled with the rad on auto supra's so here's another shot....

The cooling system is cooling as much as possible but the trans is running extremely hot and therefore heating up the rad beyond it's maximum cooling potential? That would go along with the prob were it only runs hot when it is revving....

Any way to check trans temps?

 

You mentioned that this first happened after driving on the freeway for a while. Had you worked on the car prior to that drive?

You also mentioned the fan clutch and fan. Did you change both the fan and clutch, or just the fan itself?

It seems as if you have changed everything that is cooling related. Is there any part still unchanged since this started happening (aside from the engine itself)?

 

good idea, I had a 20r that the clutch on the fan had failed

 

Good to know.

 

Rajunz, excellent info!

The plate is NOT on the engine, I made two small plates to block off the actual ports (they don't look quite as nice as yours, but they work), but the main cooler plate is not on there. Good thought though. Also, I love the idea of filling through the tee, I'll have to give that a shot.

I didn't work on the car prior to that drive, so it's not like I may have messed something up/forgot something. All was well, then suddenly not so much.

I replaced the clutch only, not the actual fan itself. Seems kind of fool-proof It blows plenty of air.

About the tranny temps, I had considered that. I once had a Dodge that was giving me grief in that regard (big surprise there). I've been running a large aftermarket trans cooler in the Supra for just that reason.
I constructed a brass tee fitting and installed a temp gauge in the trans cooler line just to be sure that was not my problem anyway, and the temps are considerable lower than the coolant temps.

----

I may have made something of a breakthrough today however. I was looking into measuring the Ks square-wave signal with an oscilloscope to see if the AFM was making it run too lean, and when I wiggled the AFM connector wires, a small unlabeled relay near there started to click like mad. Everytime I would tap the AFM wiring, the relay would click on-off-on-off really quickly. I have not been able to identify this relay yet, but now the car will hardly stay running so I hope I didn't fubar the relay somehow. So now I get to dig into some wiring, lol what fun.

*** ALSO, CAN SOMEONE PLEASE MEASURE THIER AFM PER THE BOOK AND POST UP THE RESULTS *** I would like to compare mine to a known-good running car. I measured the various resistances on it, and they come up higher than the book says they should be, but when I test my other AFM they are almost identical, even though both are higher than the book says.

I am really at my wits end with this thing, if it is not my AFM I will probably commit hari-kari any day now.