Blown Head Gasket?

[BillW]

Hi, I'm new to this Forum and to Supras. I recently purchased an 89 Supra, auto, normally aspirated, 160k miles and runs good. I think I have a head gasket leak, but I’m not sure and would like to be certain before I do the work to replace the gasket. Here’s the symptoms:
a. I’m adding a few ounces of coolant to the reservoir every few hundred miles and there is no visible coolant leakage on or around the engine and no noticeable smoke out the exhaust at least looking at the exhaust at idle and looking out the rear view on acceleration.
b. I’m adding a quart of oil every 400 miles. Again, no visible oil leakage on or around the engine and no smoke.
c. After driving down a highway for 10 minutes, the engine started to run rough like is was misfiring on a cylinder or two. I got off the highway and drove slower back home. Since then have taken it on a few short drives, and it has run fine, with no rough running of the engine
d. The oil looks clean.
e. I have not seen the temp gage go any higher than about 5/8 of full range at any time.
f. The person I bought it from has no knowledge of the head gasket being replaced.
The Toyota dealership told me “the head plugs are leaking” and would cost $1643. to fix. They didn’t mention the head gasket and I didn’t have confidence in their diagnosis, so I brought the car home. I then used a “block tester” kit from Napa to see if there were any combustion gasses getting into the coolant, but the test came back negative showing that there were no cylinder gasses getting into the coolant, at least when the car was only warm and idling.
I’m thinking maybe the head gasket only leaks when the engine is under load, like when going 70 down the highway.
Has anyone ever heard of a head gasket leaking only when the engine is hot and under load? If so, how would you test to see if the head gasket is the problem?
Would it be worthwhile to torque the head bolts and see if that fixes the problem?
Any thoughts are appreciated. Thanks.

[oregonjoe]

I am in the middle of fixing a HG leak on a 90 Supra. It started off slow coolant use with no other noticeable symptoms then grew to pushing more coolant out the reservoir and running ruff on start up.

A few things to look for. Engine cold – start up with radiator cap off and coolant above the fins (not all the way to the cap) As the engine warms up the coolant will rise just a little if normal till the thermostat opens. After the thermostat opens you see water moving around but level should remain the same and no bubbles or foam. If you have a head leak it will bubble and foam and soon the coolant will start to push out the radiator opening.

You can also do this test after the engine run for awhile but let it sit and be very careful to open the cap slowly as very hot steam will come out and is painful. Again the coolant should be at normal levels and not gush out.

Another thing to look at is the plugs. They should all be nice and tan and dry. If one of them looks like a different color (usually the same as the coolant) then it is probably burning water. Start with number 6 cylinder as that is the most common.

Retorquing the Head bolts on a already leaking HG will not do anything as the coolant is already eating channels in the HG, block and head. Old coolant is a very nasty acid!

[bayrat]

This sounds like almost exactly what is happining to mine I have a 1989 non turbo with overheating problems.
Does anyone know the cost to have a mechanic repair? about

[907mge]

most likely close to what the car is worth

[Travis89Turbo]

Originally Posted by bayrat

This sounds like almost exactly what is happining to mine I have a 1989 non turbo with overheating problems.
Does anyone know the cost to have a mechanic repair? about

It's cheaper to buy a jdm engine. And transfer all emission system over. Or anti up for a 1jz swap like I am in the middle of. More money. But u gotta pay to play with the big boys.

[windo67]

You will find that owning an older Supra is not cheap, especially if you can't do all the work yourself ., but when its running good and the tops out and you are flying down the road and you kick the turbo in may make it all worth it.