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91 VR4 wish scissors BBK wheels and tint
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Discussion Starter #1
1991 3000GT VR4, stock.
Ive only had the car since feb, and put 3000-5000 miles on it.
Usually I only take it to local meets and it fully cools off before I return home.
I found my car overheating on one of my first long(er) drives.

Wednesday I took it for an hour long drive, all freeway 70-80mph 4th and 5th gear... not pulling hills.
The temps bounced from the usual (about 1/3 up the gauge) to HOT (just under the red)
CURIOUSLY I noticed it would cool off when I got on it a little (I suspect because the coolant got low....higher revs splashed coolant around/)

WAIT a minute.... "coolant got low"
yes, I said that...
funny though, Its not leaking externally and I don't think its leaking at the head gasket.... no coolant under the dash.
no coolant burning through the plugs, and none in the oil.
previous owner put in a new OEM radiator, I put on a new radiator cap, thermostat, and rad hoses. filled with ~2 gallons 50/50 and topped off with water. (CA doesn't get that cold)

Im 90% sure that the car is loosing coolant because its getting SO hot that its just puking coolant up as steam (but the system is holding great pressure)... after my drive I parked and it boiled in the block for ~3-5 minutes and 15 minutes after parking I used a rag to open the radiator cap... still hissed

Has anyone seen this before or have some hints to check?
 

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There are many threads on the topic, but I will take the first bite...

If you are uncertain of coolant loss, then take notes on two things while cold - level in overflow reservoir and within fill point. It is supposed to siphon from cold and "spit back" the same amount upon cooling down from operating temp.

Burp the system properly. This is often overlooked.

Verify proper fan operation and correct temperatures; first-gens use thermoswitches. You will also want to verify that the thermostat is actually opening; new does not guarantee functionality.

Lastly, perform a system pressure-test beginning with a low setting.

IF you ran it hot enough, then there is a slight chance of warping the heads which would explain certain things. For peace of mind, you can also perform a HC test.

-sent from my Galaxy Note 9
 

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Its not leaking externally and I don't think its leaking at the head gasket.... no coolant under the dash.
most likely if it is a head gasket you will not see the leak because it is going into the exhaust and is being vaporized and a pressure test may not show anything as the leak may not occur until the engine gets warm fill the coolant and warm up the car without the filler cap on and observe the coolant for bubbles if you see it bubbling that is a good indication that the head gasket is leaking the 1st gens used the old style composite gaskets not mls gaskets
 

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Yikes yea head gasket.

But if the radiator is new there could be a chance the thermocouplers mention could of been flipped and hooked up backwards.
 

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91 VR4 wish scissors BBK wheels and tint
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Discussion Starter #5
Yikes yea head gasket.

But if the radiator is new there could be a chance the thermocouplers mention could of been flipped and hooked up backwards.
I ordered a headgasket test kit (checks for combustion gasses in the coolant)

the thermo couples is something that hasn't crossed my mind.. Ill look into that!
 
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