over heating but not BHG

[djazem1]

alright guys i know there is 1 billion threads on this but i cant seem to find someone with the same problem as me. Ok so i rebuilt my top end decked the head and shaved the block put a greddy MHG with ARP studs tqd to 85 lbs. i also upgraded my turbo to a precision turbo witch is not coolant cooled so i had to buy the hose from DM that connects the two coolant lines for the turbo.

Anyway the problem im having is that when i fill up the radiator with coolant (and i did purge the system) while driving the temp gauge will creep up to 3/4 and if i get on the gas in about 3rd gear it starts to cool down again. I checked the oil and its clean as can be. Checked the spark plugs to see if they were wet or if there's coolant in the cylinders and again nothing.... i am not getting any heat in my car either.... someone told my heater core could be bad anyone have any advice on for me??

Thanks, Azem

 

[jdub]

Is the upper rad hose getting hot when it does this?

You heat is likely a different issue...the heater control valve is not working.

 

[Isphius]

It sounds like you have air in there. If it was really "overheating" the temp would not come back down quickly. And never rule something out just because you changed it, espeically when you change something. Always keep an open mind when diagnosing a problem. Have you checked the wire that connects to the temp gauge? That can corrode, but that usually causes it to read off/zero. how did you purge the system?

 

[RiyadYar]

sounds like air is in the system try burping it

 

[CyFi6]

Sounds like there's a big air pocket in the heater core to me... Same thing happened to me once. If the valve was stuck closed it should still get warm eventually since its not 100% shut off even when in the closed position. Make sure you get the air out of the heater core if this is in fact the problem, because when i was driving at some point the pocket of air freed and went into my engine= instant overheat.

Did your cooling system take as much coolant as it was supposed to?

 

[CATarga]

Non BHG over heating issues are usually one of three things, bad water pump, bad t-stat, collapsing hoses.

With it cooling down when getting n the gas it seems like either an airflow problem or a coolant flow problem. Did you replace the water pump at the time of the rebuild? Any noise coming from the fan clutch, do you know if it is engaging? Does the temp only rise when on the highway.

It could be a blocked heater core, but it would seem if it is blocked by air/corrosion that increasing engine speed wouldn't change the flow enough to cause the temperature drop.

 

[djazem1]

Is the upper rad hose getting hot when it does this?

You heat is likely a different issue...the heater control valve is not working.

yes the upper hose it hot not to the point where you cant hold it but its pretty warm

ok than i wont worry about the heat just yet

 

[djazem1]

It sounds like you have air in there. If it was really "overheating" the temp would not come back down quickly. And never rule something out just because you changed it, espeically when you change something. Always keep an open mind when diagnosing a problem. Have you checked the wire that connects to the temp gauge? That can corrode, but that usually causes it to read off/zero. how did you purge the system?

i read another thread that said to purge it i need to put the car up on a hill or jack the front end up and let the car run with the cap open. I got a lot of air bubbles when doing this but nothing significant.

and yes the gauge was broken but i soldered the on wire straight to the connector because when the connector broke off the was not enough wire sticking out to solder it.

 

[jdub]

Here's a better idea. Take your t-stat out and remove the jiggle valve...test it to make sure it opens (all the way) at the specified temp (should be 190 degs). Sounds like your stat is sticking part way open...the upper rad hose should be very hot to the touch. The t-stat may need to be replaced. Replace the rubber gasket regardless.

Removing the jiggle valve does 2 things:
1 - You get a small amount of flow preventing back pressure that can hold the stat closed.
2 - It allows air to clear the system quickly...you will never "burp" the system again. (make sure the hole is at the 12 o'clock position)

Another cause for this type problem is a partially clogged radiator or a fan clutch that is not working properly. A clogged radiator will usually show a higher than normal temp and it stay there...doesn't seem to be the case here. A fan clutch will though...temps will go up, then drop as air flow from car movement increases.

A pressure test of the system is also a very good idea.

 

[s383mmber1]

When the car is running, see if you can go to autozone or whoever and grab a coolant burping bucket. Use that, and when you do, see if any small air bubbles are comming out of the cooling system....

 

[djazem1]

you guys are such a great help i think the tstat is getting stuck cuz i had it off and damn was it hard to push it down and when i did it was very rough and it would only open like 1/4 of the way it wouldnt open enough so that the spring even compresses....i think i found my problem im going to autozone right now to get a new tstat ill let you guys know how it turns out

 

[djazem1]

When the car is running, see if you can go to autozone or whoever and grab a coolant burping bucket. Use that, and when you do, see if any small air bubbles are comming out of the cooling system....

yes there is little bubbles coming out once in a while....does that mean theres air in my system?

 

[jdub]

Get a Stant SuperStat or a Toyota OEM at 190 degs. Test it (I've had new ones that are bad) before you install.

Pressure test the system. The air could be from your heater problem (trapped in the core due to limited flow).

 

[Isphius]

you need to really get the front of the car up there to burp it too. I never did on a supra but with my MR2 i had to build a ramp out of plywood and 2x4s and get the car at like a 30 degree angle to get the air up to the front so it could come out. I wouldnt drive a supra onto a plywood ramp. If you live near a warehouse you could just pull it up on the loading dock at night. or a steep driveway. just dont get caught

 

[jdub]

A cooling system in good operating order should never need to be "burped".

 

[grimreaper]

never had to burp mine, even after draining and refilling entirely (block, heater core and rad.). The jiggle valve mod must be effective

good info on our systems and cooling systems in general...

Your car has what is called a pressurized closed reservoir system. In days of yore systems were open and operated at atmospheric pressure. There was not enough heat load generated by the engine to make the coolant boil so pressurization wasn't required.

Then along came pressurized open systems. Those systems operated under pressure but were filled to less than full, say a few inches under the radiator neck. The space was needed to allow the coolant to expand so it wouldn't lift the pressure relief valve in the cap. Air was drawn back into the system through a vacuum valve to prevent hose collapses, ect as the system cooled. In effect the cooling system needed to breathe. If over pressure occurred coolant was dumped out the overflow hose to the ground. I still see people fill open system radiators to the brim and wonder why their car takes a piss. It's because they don't know they shouldn't be filling it all the way up.

Then came the closed pressurized reservoir system like we use. They're designed to be filled to the radiator brim. No air is allowed. On these systems it's a common misconception the radiator cap never opens unless there's a problem. On the contrary. As the coolant expands the cap's pressure valve is lifted and excess coolant is dumped into the overflow tank. As the engine cools coolant is drawn back into the system. This is why you need to be sure the overflow hose and snorkel in the tank are airtight, otherwise air will be drawn into the cooling system every time it cools off. I can't tell you how many cars I've seen with leaky overflow hoses and snorkels, ect. And people wonder why their cooling systems need burping.

It's the vacuum valve we're talking about here. A weighted valve will hang down and allow the system to run at atmospheric pressure as long as it can. When pressure builds or rises sharply the valve will shut and the system goes into the pressurized state. On the other hand a spring loaded vacuum valve seals the system from cold onward and is only open when the system is cooling ie; when it needs to "breathe" coolant back into the radiator.
-JJ

 

[djazem1]

ok guys i think i fixed it :biglaugh: i stopped by my uncles shop and asked him what it could be he told me a trick he uses to test the tstat he told me to put a pice of paper on he tstat to hold it open a little bit and i drove it around for a few hours like that and i didnt see the gauge move one mm above normal since then so i went to pepboys got a new tstat and gasket (thanks JDUB) and i will be installing it tonight ::w00t:::: snowart ::