PorKen

My '85 had a loose clamp at the heater valve and would loose coolant >130 mph.

One of my '86.5s had a slight crack in the seam of the heater valve which drip coolant. (Eventually, during a WOT burst it split in two.)

Both cars had leaks at the coolant pressure sensor.

All of these were 'mystery' leaks, with no sign of coolant at standstill.

Jim @ EuroWerks

You won't be looking for the rusted plug. You'll be looking for the one plug thats cleaner than all the rest.
I usually pull the rad cap, fill it to the overflow at the coolant tank, then pressurize the each cylinder at TDC and wait for it to either push coolant out or bubbles. Good luck. No, headgaskets aren't fun.

Benton

I'm sure this has probably already been taken care of some way or another, but our track car had a mystery leak as well. Turned out there was a pinhole-size break in the head gasket that allowed water to escape the water jacket and spray onto the exhaust manifold. The water was vaporizing immediately, so no trace of the leak and when unpressurized, it didn't leak. Took me a long time to find that one.

Lizard928

If anyone remembers his threads after this it was a hole in the waterpump casting that was leaking coolant

IcemanG17

TOO FUNNY.......

Bill helped me change the waterpump yesterday & we were able to change it without pulling the damper-pullies......it took us 3 hours flat....when we pulled the old waterpump we foudn the gasket was cracked right where the leak was....so I was optimistic we fixed it....

Today the water level was exactly the same as yesterday so I thought it was good....go out for my 1st session...car is fine, temps are great,.....then I came in and parked it......time for the next session it was 1/2 a gallon doan

It must be some headgasket leak that doesn't effect compression......I dunno....

James Bailey

Kibort would add the stop leak and run it for a few years.....

Benton

Exactly--no coolant in the cylinder; it was just leaking from the water jacket to the outside. The cylinder was still sealed, but apparently someone along the line neglected the coolant and probably didn't use distilled water, so the head gaskets looked pretty rough.

SteveG

Just about everything has been mentioned. Let me add the water bridge to the list. I had a sloooow disappearing act, kept adding coolant and it would go low in the res again, and found coolant in the low spots near the bridge. I sopped it up and it would reappear. I replaced the gaskets on the bridge. Maybe you have multiple leaks?

Opelotus

I almost mistook a leaking water bridge for a bad head gasket. Coolant ran across the head-to-block seam and congealed.

Bill Ball

Brian:

Don't go blaming the headgasket yet. You may have just had to top it off after remaining air burped back into the reservoir. See if it goes down again. I'm hopeful we got it, BUT since you described it earlier as "disappearing" coolant, it does not sound like an external leak.

IcemanG17

Good point.......once I fix the alternator I will test it

Water bridge gaskets also look old....but there was no calicum deposits to show a leak...

Bill Ball

Fix the alternator?

GeorgeM

I have a leak that is dripping onto the a/c compressor bracket, then onto the floor. I can see the white G-05 stains and a drop sticking to the side of the block just below the HG and just forward of exhaust manifold pipe #2, but can't tell if it's travelling from somewhere else. I'm about to unbolt the a/c compressor and move it over to get a better look, can't see enough with a mirror to pinpoint it.

It also appears to leak mostly after sitting a while post shutdown rather than while the motor is running.

Any common leak on that side of the motor that I should look for?

jcorenman

Are you adding Redline "Water Wetter"? One of the nice things about G05 coolant (or hard water) is that it leaves distinct white trails where the leaks are... unless you add Water-Wetter

atb

I had a mystery leak turn out to be where the alternator pulley rubbed a small hole in the lower rad hose. When the car was parked the hose had plenty of clearance and wouldn't leak. Under the dynamics of driving, it would make contact, it wore a hole, and would leak.