wds928

My 94 GTS was recently overheating, getting close to red, but not there yet.

I replaced the thermostat with a 75 C unit, new O ring, new t-stat housing seal thingy, replaced the coolant, burped the system, seem to have the air out of it.

Was running it today, testing the temperature with the multimeter temp probe. The left side (facing engine) radiator hose to the intake gets up to temp first, then the other side radiator hose comes up to temp, which indicates to me the thermostat is opening properly. Then after running in the driveway for a bit longer, 5 minutes or so. temp guage gets warmer and the temp probes shot to high 190's, low 200's and I smell coolant, but can't see any. Then a small puddle of water left in the front intake webbing from the flusing starts to boil and the temp probes are around 212 F or so. The dash guage is running in the high white area, but not in the red area. I shut the engine down at that point.

No apparent leaks, the hoses were hot to the touch, and firm, so there seemed to be plenty of pressure (didn't check the pressure cap though).

Has my water pump impellor decided it no longer wants to spin on the shaft???? Opinions anyone??

Is the anyway to check this out without pulling everything apart?

IcemanG17

Bill
Sounds like a bad water pump? How long ago did you change it? Since the rest of the car is running fine (i.e. T-belt still intact) you might be right about the impellor? I did read a post about radiator caps not holding pressure, but your situation sounds much more serious!
Brian

Rich9928p

When you say it wasn't in the red, but close to the red, how close was it? What were your driving conditions - Fast, driving up hill, A/C on or just slowly tooling around town?

Most people are used to "normal" being in the center of the gauge and get nervous when the needle creeps up even to 2/3rds. On later model 928s, the temp is normal when in the top 2/3s and isn't hot until it the needle is in the red.

What is an easy way to check to see if your cooling system is working? Drive hard, if it gets into the red, let up a little. If the temp cools down to below red, then your cooling system is working. If it never gets into the red under normal driving, then you're OK.

FYI, my '87 runs just under the 2nd white mark on cool days, and just over the 2nd white mark on warmer days with the A/C cranked up. Running hard, the needle moves up but doesn't hit the red. My GTS is similar - nomally reads a little lower. But when run hard will move up towards the red.

When I had an '83 and '84 928, they always indicated lower on the temp gauge, but would run up above 2/3rds on hot days with the A/C.

MikeN

Running 190 to 200 is normal........but if yours is running 212 or more with it just sitting......then I believe something is wrong. Could be right about the W/P impeller. How are the two fans running?
Make sure they are both coming on and running nice and hard.......and the same speed.

wds928

Mike, the fans did not come on at all.

Rich, mine has always run in the middle between the two white marks, even with the 83C thermostat.

I wasn't even driving it yet, just sitting in the driveway. The car has 122,000 miles on it and supposedly, the PO had the t-belt and water pump done at 90,000 miles.

shaaark89

if the fans didn't come on then that's your problem. with no airflow over the radiator, there will be less than ideal heat exchange. if the problem is less apparent while driving (air flowing over the radiator even without the fans running) then it's very likely a fan issue.

Garth S

The fans must come on at those temps - my S4 would trigger its fans long before those temps id idling in the driveway: time to start the multimeter diagnostics - begin with the fuses..... ( a quick check is to short the air temp sensor contacts on top of the intake manifold with the key off - this will fire up the fans if they are working, but will not confirm the rest of the normal fan start triggers).
If in doubt of the impeller at a latter point, drain and save the coolant and fill the block with water: remove the thermostat housing and start the engine briefly. If the impeller is firmly attached, it will be obvious ... I've done this stunt with a hose stuffed into the inlet side and 'sealed' with a rag - a quick way to flush the block if the fun drain plugs are avoided.

wds928

Tom, Garth

Thanks for the input. The fan fuses check out ok. I later realized that the fan's won't come on with the hood open, due to the hood switch interfacing with the fans.

Tom, it was a nice day here today and I did drive it some at speed (60 to 80) then pulled off and checked the readings. They were in the low 190's, with the dash guage between the 170 and 210 mark. So this seems ok, although the temp did creep up a bit as the car sat. The fans never came on, even with the hood shut.

I'll drain the new coolant and fill the block with water and remove the t-stat housing to check to see if the impeller is working.

Part of the fan problem may be the a/c isn't working. I press the a/c dash button and the compressor doesn't engage and the blower motor doesn't work.

Comparing the dash gauge to the multimeter temp reading leads me to think the temp switch/sender may be bad. The gauge first far left white line is 110 F, the next is 170 F, the third is 210 F, followed by Red. The gauge was getting close to the 210 mark, but used to normally run between 170 and 210 marks. Now that I write this, then maybe the gauge is ok as well as the temp sender. When I shut the engine down and read the temps with the multi meter, the t-stat housing readings (intake and output) were 210 F or a bit higher. The liquid it the webbing below the oil filler/thermostat housing appears to be a small accumulation of oil and coolant (due to a leaking oil filler neck gasket and changing the coolant). Kind of messy looking, but this is what was boiling when I shut the engine down.

wds928

I unbolted the thermostat housing and started the engine. Coolant is being pumped from the rear of the intake manifold to the front, so I guess the waterpump impeller is ok.

It's looking like the fan controllers/wiring and may be connected to the a/c problem.

MikeN

The fans will not come on with the hood open and the engine not running......with the engine running the fans are *supposed* to come on....even with the hood open, otherwise the engine would overheat even when at idle.

After about 5-10 minutes of warm up from a cold start the fans should start a cycling process of coming on then fading back off, again, again and again. If they are not doing this......you have a problem with the fans.......or most likely one of the items that help control them.

Randy V

Mike has it right on the fan control. I'd guess a bad connection on the fan temp switch or a failed switch.

In either case, now that you have it narrowed down to being a fan problem, should be relatively painless to repair.

wds928

Randy:

Thanks. I'll be testing the fan controller and temp switch tonight after work.

fst951

They also offer a lower temperature fan contorl switch, I believe. Might help to run the fans a little longer and sooner.

Good luck.