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1988 MA70 Turbo
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21 Posts
Discussion Starter #1
Hello again,

So my car leaks coolant out of the expansion tank hose, seemingly randomly. Sometimes I find a few drops in the morning, and sometimes it dumps a huge amount of coolant randomly. I have no idea why this is happening and am looking to the forums before the mechanics.

Story: After taking a little road trip, after about an hour and a half of driving at 140km/h in 25-30 degree (celcius) heat, basically the whole time, my coolant got a little excited and exploded. My expansion tank cap blew off and the cooling system evaporated/steamed out of the system. I caught it right away as my water temp needle climbed and my CEL came on, noticed steam from my hood and pulled over immediately and shut off the engine. The needle climbed to maybe 2/3 of the way up the gauge (mine usually sits one tick below half, so it didn't get crazy hot/overheated. Between catching the needle start to move and having the engine off, it was at most 15 seconds.

I thought I blew my headgasket, but there was no leaking from the head, no exhaust smoke, and after getting it home and inspecting everything, flushing the cooling system multiple times and checking the oil, there was no signs of a BHG. It's been about two months since then and I have driven the car about 2000kms, no heating issues at all, but every now and then my coolant will be low, with some drops on the ground from the expansion tank overflow hose. I can tell it's from there because my intercooler has coolant on it right below the hose opening. There is never any coolant dripping anywhere else.

I changed my thermostat to a 180F, used 50/50 pink concentrate and water, and changed my coolant temp sensor. Everything works and my temp holds in the appropriate place.

Has anybody ever experienced this before or have any idea what the issue is?

Now that it's already snowing here in Canada, I am parking the Supra and was planning to get a lot of work done. Coilovers, Mercedes/Evo brakes, facelift taillight swap and some other little things. I figured since it will probably be sitting 6 months, I should consider doing the headgasket. My motor is healthy, only 120k km on the entire thing (was pulled and resealed/refreshed at 100k kms) and I don't really want to pull the block just yet as I plan to JZ swap someday so will just be going with a composite gasket for now. Issue is, the engine was done 11 years ago and I have no idea if they torqued the head bolts appropriately or not, or if they even refreshed the head when it was pulled.

Thank you.
 

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1987 Toyota Supra
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310 Posts
That's a classic blown head gasket symptom.
One or more of your cylinder fire rings on the head gasket are slowly giving out.
This allows gasses and pressure from the cylinder to be forced into the coolant system, causing exactly the symptoms you are describing.
Fix it now before you cause more damage.
Overheating the cylinder head 1 or more times from loss of coolant has the potential to cause some irreversible damage FYI.
There is usually no sign of external block leakages with this type of failure.
Only that you over pressurize and start loosing all your coolant.
Then shortly thereafter blowing the engine due to overheating.

If you want to verify that this is in fact what's happening, run this test:
- combustion leak test - checks for exhaust gasses in the coolant.
 

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Registered
1988 MA70 Turbo
Joined
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21 Posts
Discussion Starter #3
That's a classic blown head gasket symptom.
One or more of your cylinder fire rings on the head gasket are slowly giving out.
This allows gasses and pressure from the cylinder to be forced into the coolant system, causing exactly the symptoms you are describing.
Fix it now before you cause more damage.
Overheating the cylinder head 1 or more times from loss of coolant has the potential to cause some irreversible damage FYI.
There is usually no sign of external block leakages with this type of failure.
Only that you over pressurize and start loosing all your coolant.
Then shortly thereafter blowing the engine due to overheating.

If you want to verify that this is in fact what's happening, run this test:
- combustion leak test - checks for exhaust gasses in the coolant.
Thank you for the reply. I suspected something was up in the head. I will probably just jump straight to a head gasket replacement.

That being said, I don't want to pull my block right now, unless after pulling the head It appears I need to.

I know this means that I must get a composite style head gasket and it won't be as good as a metal one.

How much power can I push on a composite HG and ARP studs/bolts? Assuming the rest of the motor is healthy. Right now I only have a 3in turbo back and an intake.

My goal is 300-350whp. I'm not 100% how to reliably attain this. I assume boost controller and fuel mods, maybe dyno tuning.

I plan to get gauges too for this purpose.

Will my new headgasket hold up at this range? At least for a couple years?

Any recommendations for the gasket? Toyota genuine top end kit?

Any other tips or recommendations appreciated.
 
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