Fabio421

Darn, you posted while I was typing. I do need to type faster. Looks like you thought about the impeller load thing too. Hey........ you know what they say about great minds.

FlyingDog

That's what I thought too, but I didn't know for sure.

Jim M.

Two trains of thought on this:

1. Do you have an air bubble in the engine preventing flow? These cars need to be burped to get all of the air out of the system.

2. How do you know the temp guage is reading correctly? Try using another (direct reading) temp guage in one of the manifold ports. You say it's overheating because the guage goes into the red. Does it actually spew fluid out the overflow?

As someone already mentioned, the thermostat closes when warmed up, to block a port, forcing the water flow through the radiator.

Jim Mayzurk
93 GTS

jeff jackson

thermostat has to be "o" ringed on the radiator side of the t-stat...and the seal at the rear of the housing the t-stat is mounted in,is a critical part of forcing coolant flow through the radiator when the t-stat opens...If indeed your water pump is flowing fine, and the car is overheating, pull the t-stat again,and look in the rear of the housing, directly behind the t-stat mounting flange...the rear seal is located there, and it must extend from its mounting flange face by at least 1/16" or so, to prevent the coolant from being recirculated in the block, and force the coolant flow through the radiator when the t-stat is open. This was the culprit on my hot 86.5....

Bill Ball

Yes, the T-stat is OPEN initally allowing flow through the radiator bypass. As it warms up it CLOSES, blocking the bypass. Remove the radiator neck and make sure you have it installed properly and that the seat inside the water bridge against which the T-stat closes is in good shape. If you cannot see the black seat surface, it is corroded. The seat is rubber coated metal and is hard to see and a bit hard to replace. You have to get something under it and pry it up a little then pull it out with needle nose pliers.

George Suennen has a page on this:
http://sis125.berkeley.edu/928/wk-thermostat.html

Look at his thermostat and seal pictures linked in the article.

TAREK

Thank you everyone for your help. Greatly appreciate the insight. I had pretty much looked into all of the suggestions here, including the Thermostat rings, boiling water test, using an IR thermometer to confirm temperatures at various points of the system, etc.

I put it together and it now runs fine!!!!!!! not overheating!!!!??? My guess is that while the thermostat passed the boiling water test exactly the same as the the new thermostat, it most likely had been stuck prior to that and I un-stuck it during the test. It gave me a false impression it was ok as tested. Then I got busy troubleshooting everything else that also checked out ok. The lesson: keep it down to one variable at a time

Thanks again everyone

Bill Ball

Glad to see you are back in business.

Jim bailey - 928 International

Tarek ......"The lesson: keep it down to one variable at a time"...... GREAT WORDS OF WISDOM ! You see this RULE violated at the race track far too often and people simply get lost trying to make a car handle. Often can not even get back to their original better set-up. Good job getting your problem resolved.

TAREK

Thanks Jim. I'm usually methodical (read SLOW and over-analytical by other people's standards) and have been progressing slowly on various other projects, but I violated my own rule this time. I got lazy and didn't throw the Thermostat back in there to verify before proceeding.

One HUGE ongoing project is optimizing the suspension of the extra-widebody (ala 935 but wider). The car was never designed for an 80 inch wide rear track, so compensating with off-the shelf and aftermarket suspension components will require a formal Design Of Experiments exercise...especially for a suspension novice like me. It might actually work to my advantage that I don't know enough to be dangerous and will always want to leave bread crumbs for the return path. The thought of labor intensive work on the suspension for every variable is already draining and causing me to procrastinate.

TAREK

Thanks Bill. Put her to the real test today in hot Florida with AC on full blast in traffic. CTemp gauge cimbed to 3/4 mark during extended idle in traffic, but no threats of climbing further

FlyingDog

Good job!