guardrail9

So I have been dealing with an overheating issue lately on my stock 1993 GS300. I cannot for the life of me figure out what it is and figured I would post up on here to see if anyone else has ran across a thread or write up or experience that could lend an idea or help to solving this one...

Here is what I have come up with recently. The car has 223xxx miles. It runs amazing no smoke no misfire and great acceleration premium gas, all fluids changed maintenance up to date by me. it will sit in park for hours in mid day heat with the ac full blast, heat full blast and not overheat one bit. it will drive for long distances through downtown traffic, highway traffic, hills etc with the hvac system turned off but the minute I turn the hvac system on ac or heat full blast it gets hot. not pegging out the gauge hot but hot enough to make the coolant start to vaporize and the familiar click of air in the radiator. only once has it ever obviously overheated on me but i pulled over before it got past 3/4 here is all the repairs I have done to it. I have not experienced any coolant loss either besides when it overheated bad

2x new radiators (second was warranty)
new tstat with jingle valve
new clutch fan
new fan switch for the efans
countless coolant flushes to where its boiling/freezing point is perfect
new worm style clamps on all hoses
new belt and belt tensioner
tbelt and waterpump are still before scheduled maintenance
ignition timing set and rechecked

heres all the tests I have done that passed every time.

multiple block tests (early cold, hot, after a long drive)
pressure tests at same times
compression test
leak down testing

as stated before I am having no other driveability issues other than overheating when the hvac system comes online. any help would be awesome. thanks

Nixspeed

Have you tried replacing the coolant temp sensors? If they are a little out it could cause your gauge rise issue. Ic you do replace both. One is for the gauge other is for the ecu which is more important.

Salcedo90

Have u tested for a Blown Head Gasket???

Nixspeed

He said he has done multiple block tests. Leak down and such should reveal a bhg.

Nixspeed

Actually I have a used 94 GS 2j just sitting around if you need any parts off it. Sensors etc.

Titten

Are the aux fans working as expected? And are you sure there's no bubbles in the cooling system?

guardrail9

tested for BHG passed off of multiple block testers and diff brands of test chem at diff engine speeds and heats... passed compression and passed leakdown.


def no air in the system. have both burped the system traditionally with a attached funnel to the radiator and filled the system with a vac filler tool I have to no avail. coolant still not loosing any.

only thing I can think of is a seeping headgasket that only shows on acceleration when warm or the fact that this motor is hating life at 230k... we will see what the cooler temps from fall and winter bring...

TheMole

iTrader: (13)

Sounds like a strange issue especially that it passed all the diagnostic tests. Did you replace all the parts you mentioned yourself or at a shop? Did you experience this problem all of a sudden or after something was done to the car?

guardrail9

i replaced all the parts myself at my work which is a shop. reason its so easy to test retest and retest the retested results lol experienced the issue as the temps of summer came along always had a slight overheat but that was from a cracked radiator and lack of oe fans so i replaced those parts and now that ive gone over pretty much the whole system i was at a loss for why its doing this

TheMole

iTrader: (13)

Haha nice that explains the ease of running those tests.

Probably sounds simple, but was the thermostat installed with the jiggle valve at the 12 o' clock position?
Is the thermostat OEM or aftermarket? I've heard of some aftermarket ones causing issues.

If thermostat is good, try checking out the Coolant Temp Sensor as Nixspeed mentioned above. It is green-colored and located near the front of the engine next to the exhaust manifold. You can test it with the steps below taken from alldata:



Using an ohmmeter, measure the resistance across the terminals.
at -20°C (-4°F): 10 - 20 k ohms
at 0°C (32°F): 4 - 7 k 0hms
at 20°C (68°F): 2 - 3 k ohms
at 40°C (104°F): 0.9 - 1.3 k ohms
at 60°C (140°F): 0.4 - 0.7 k ohms
at 80°C (176°F): 0.2 - 0.4 k ohms

If the resistance is not as specified replace the Sensor.

I still have another year left on my alldatadiy subscription for the 1GS so let me know if you need to look something up and I'll check if it's available. Good luck!

guardrail9

yeah it does make it easier owning all the tools for the tests and working on it. i have bits and peices of the 1gs service manual stored away. and i have access to Mitchel services. but their service is how do we say very user unfriendly.

the tstat is aftermarket its a staunt fail open with a jingle valve installed on the mark it says in the service manual. but ill check more into differences between oe and the one i have. On the sensors does alldata have a theory of operation write up or anything or what they control more specific than just ecu and guage? I know the guage one is right because i can hear the car overheating if i push it and make a long drive

TheMole

iTrader: (13)

Got the following regarding the sensor from alldata:

PURPOSE
The Engine Coolant Temperature (ECT) Sensor monitors coolant temperature with a thermistor whose resistance varies according to engine temperature. The Engine Control Module (ECM) uses this signal to control open/closed loop operation of the fuel injection system, overdrive on electronic transaxles, electronic spark advance, idle speed control system and other functions.

OPERATION
The ECM sends out a reference voltage of approximately five (5) volts to the ECT sensor. As coolant temperature changes, the internal resistance of the sensor will change, causing a varying voltage drop across the sensor. The ECM reads the voltage drop across the sensor as engine coolant temperature.

Nixspeed

That ecu temp gauge controls in part your fuel trim. If it thinks its colder/hotter than it really is it will spray more or less fuel to compensate which may cause lean condition or over rich causing a late burn which would cause extra heat as well.

guardrail9

ill try the sensor but not hopeful. because lean would cause other issues and CEL unless it was so small but then i dont see it overheating if the fuel lean would be small. easier way to rule this out would be how much change in fuel trim does it give. right now im wishing this thing was odb2 lol