Any Tips on changing coolant on a 91 TR?

If you are losing coolant into the combustion chambers I doubt any "stop leak" product will fix it.

Removing the thermostat allows circulation when the engine's cold.

How much do you add?

Are you allowing for normal expansion?

The system is never full to the top when cold.

 

I add aprox 0,3-0,5l every 100-150km. Currently i fill it up until half of the expansion tank is full (exactly to the border between the upper and the lower part of the expansion tank so i can easily see if coolant fluid is missing).
Checking is done after the car had time too coold done over night.
One time i opened the expansion tank cap immediately after shuting down the engine. There was still about 1-2cm gap between fluid and the top of the tank (not the top of the filling neck).

 

Oil contamination? Any "foamy" stuff on the filler cap?

If you've replaced a head and gaskets twice you apparently had a big problem before. You might have a crack (cylinder liner?)

Have you checked spark plugs? The affected cylinder/s would likely look different if it's from the head. If the cylinder liner it might just foul the oil.

Have you examined the water pump? Maybe it only leaks when driving and you don't see it come out.

 

No foam seen on the oil filler cap or on the filler cap indicator.
Full story on this problem:
- car used up about 0,5l cooling fluid on 100km so it went to the repair shop
- they found out that there is exhaust gas in the cooling system and
recomended to change the head gasket on the right cylinder block.
Engine was also running hotter (but still no overheating, just heating up
much faster than currently)
- gasket was changed (but no visible damage was seen)
- head was checked and some planarity work was done for safety (and also checked for any cracks)
- after this the engine was running much better but after around 1000km the
same problem happend (used up coolant fluid). According to the mechanics one piston looked like there was water inside (different color of the surface, checked whe the spark plug was out).
- Engine out again, head removed. No visible damage found on the gasket
- bolts replaced and x-rayed the head. X-ray showed 'something uncommon'
but seemed not to be related to the leak problem
- we decided to replace the head to be sure the problem is gone (was the
second year in the repair shop at this time ...)
- after re-installing everything engine was running much better than before
but discovered massive oil leak on one cam (seals all new) => engine out
again, new seal again.
- engine was re-installed end of last year so it was only driven 150km.
- Since beginning of april this year it was driven around 200km. Water and oil temperatures all ok (water normaly at around 75-80 °C, oil about 70°C).
- Water is checked after every driving session (about 50km each).
- CO2 test done - fluid turns from blue to light green if done at idle without
driving.
If the test is done immediately after driving with higher rpm's (sometimes 5000 and up) it changes directly from blue to yellow.

 

Sounds like your car hasn't been home much. Sorry to hear it.

How about the other head?

You could remove all the spark plugs and pressurize the cooling system. See if any water comes out.

Leakdown test with radiator cap off, check for bubbles.

Still a possibility of a cracked liner.

Just curious, where are you located? Who does your work?

 

You are right, the car was not at home very much in the last two years. That's why i had to get a 'backup' Ferrari (355 GTB) last year. But still love driving the testarossa more than the 355. Maybe i'm too old for the 355 ;-)

Just came back from a 200km trip with the testarossa. Had the water filled up before we left. Now after 200km i (carefully) opened the expansion tank cap immediately after the engine was stopped. The hot fluid is around 1cm below the top of the tank which looks ok to me. Oils and oil cap still looks fine, no foam. Same with the cooling fluid, no foam. Temperatures had been all ok. Even during stops at traffic lights the temperature was below 90°C.

Regarding my location - some thousand kilometers east from you i guess (south of germany)