I am at wits end and need help for solving an overheat at idling.
1980 928, 16v 77000 mi, driven <3000/yr.
After a rigorous drive, min 1/2 hr @76F ambient temps, and reaching normal engine operating temps of 195F per Auto Meter electric temp guage sensor installed upper hose, no overheating. Once left at idle for 5 to 8 minutes, Aux A/C fan on at ~195+, clutch fan on and apparently functioning normally, both temp meters elevate to warning light & Auto meter reads 212+, at which time I shut engine down to prevent excessive overheating. After elevated temp ~210, getting car back on road with air flow, coolant temp comes down. Seems like an air flow problem ?? Original radiator replaced in 1995 @ Browns with Behr for complained of "overheating". Coolant previously changed 1998, SHAME ON ME !.
Current Attempted fixes completed:
1.) new thermostat changed 83 deg; new 13psa coolant cap.
2.) coolant flushed/changed (Zerex G 05) and pressure tested @13 psa; burped coolant via cycling heater valve 1/2 doz. times; coolant level checked.
3.) Co2 gas test.
4.) timing @ 23deg advance.
5.) radiator flow check, via "hand on radiator fan side grill" hot checking for uneven temp.
6.) Fan clutch filled with two bottles of Toyota 10,000 silicon oil per various Rennlist theads.
7.) timing belt checked and properly adjusted
8.) new 16" Spal Aux pusher fan, 83 temp switch, activates @~195 F coolant temp.
What have I missed, I'm at wits end and open for opinions.
....BAD fan clutch ?
....Water pump failing ?
....Radiator clogged?

Update: As suggested by several knowledgeable individuals, the solution ended up being a bad fan clutch. The tried two bottle Toyota silicone repair did not work for my 70,000 mile fan clutch. I did not have any experience as to what proper air flow should be, I wanted to think that my initial silicon repair/fix was not the problem. I took a gamble and located used fan clutch assembly on ebay, and immediately noted the stronger air flow via new/used fan clutch. No more over heating @ idle.
Thanks and much appreciation for the commentary and helpful suggestions in helping me arrive at a solution. In retrospect it was a great learning experience interacting with all the folks !

 

with the car cool , what happens when you spin the belt driven fan by hand, how far will it spin??
Is there noticeable friction while you turn it ?
If the fan has a good amount of drag all the way around a full rotation then i woulkd suggest to pull the radiator and back flush the external fins as well as the inside to see if anything comes out also replace the thermostate, sometimes you can get a bad one also replace the coolant bottle cap and the heater control valve and short hose. with the aircleaner off inspect the head gaskets along the inside of the V if you see white crust or white drip trails then you need new headgaskets

 

23 degrees of advance? isn't that a lot? I certainly don't know all that much about timing of engines, but that seems a bit high to me from my armchair perspective.

Also, did you install the fan in the right orientation? From the description you called it a "pusher" fan, so I gather that it goes in front of the rad. I suppose you would have noticed if your flow check was not pushing air the right way, but it may be possible that you installed the fan backwards and so it isn't cooling properly at idle.

Just my $0.02, I hope you get it worked out.

Good luck!

 

When you did your thermostat, did you replace the seal behind the thermostat, (this is the smaller one that goes into the water jacket)? That seal disintegrated on me causing my S4 to run REALLY HOT.

 

I'm thinking NOT thermostat if it cools when back on the road, but bad flow. _Maybe_ the pressure cap, but airflow or coolant flow through the radiator are more likely - and coolant flow is most likely, imo.

The cap is easy to test at your FLAPS, and to replace, but I'd start with an infrared thermometer inspection of the radiator as it warms. FLAPS might have infrared thermometers, too, but they're cheap (relatively) and useful around the house.

http://www.amazon.com/s/ref=nb_sb_ss...refix=infrared
http://shop.ebay.com/?_from=R40&_trk...All-Categories

That said, a backflush through the radiator fins is a good idea, too, and a good first thing. Be gentle.

There are other possible causes that are worse to MUCH worse, but i'd start with the simple stuff.

BTW, are you _sure_ of the temps you've seen? It sounds like you've done your due diligence, but I once chased an overheating problem, throwing parts at it, and it turned out to be ONLY a bad sensor, which set off the gauge and warning lights. Time and $$$ down the drain.

 

2nd on the little seal behind the thermo......both 928's I changed it on, it really made a difference!!

Its possible the radiator is clogged.....since you changed the fan and it does not cool off at idle...which it should....consider an all aluminum radiator or have your existing one cleaned

1 last idea...since you live in socal...where it rarely gets cold....reduce your coolant-water % to maybe 25% coolant 75% water + a bottle of water wetter.....thats what I ran in my street S4 with no problems...even climbing hills in 100F heat with the AC on at a spirited pace

 

Timing specs. 23 degrees. (He's following the book verbatim).

Wasn't the behind-T-Stat O-ring added for the 4.7 valve cars? I don't think this car has that particular potential issue.

 

The thermostat sets the minimum temp of the engine after warm-up. Once open; heat transfers to the radiator, subject to water and airflow. If flow is inadequate and the thermostat is fully open, the problem is the water pump, or radiator restrictions. Check radiator first, they’re more common, easier and cheaper to fix.

Airflow also varies, at high temp, at idle, the fans provide airflow. That setting comes from the thermostatic clutch on the belt-drive fan and from the temp switch and AC operation for the electric fan on pre S4’s. This all interacts so a car that overheats at low speeds but is OK at high speed often has airflow problems. Due to a fan clutch, electric fan, or thermo switch, or both. A car that overheats at high speed often has water flow problems, usually a restricted radiator. A car that overheats right after startup has water problems, a thermostat stuck shut, an inop water pump, a plugged radiator, or no coolant.

Lower temp thermostats let the engine run cooler, if there’s radiator capacity. If your car overheats, a thermostat only helps if it was stuck or plugged and is restricting coolant flow. When the thermostat opens, it expands backwards, against a gasket behind the thermostat, closing the passage and forcing the water through the radiator. The gasket deteriorates and the thermostat can’t completely close the passage, so some of the coolant recycles through the engine, getting even hotter. A low-temp thermostat doesn't flow more; it flows sooner. Fan operation must be coordinated with the thermostat to stay cool. Match the thermostat temp to the fan switch, so the fan doesn't run before the thermostat opens.

Flush the debris out that gets packed in the condenser and radiator, blocking airflow, with a hose from the front, but don’t bend the fins. Redline Water Wetter made it almost 3 needle widths cooler. I've had good results running the Prestone cooling system cleaner through the engine. Follow the directions about removing all the old coolant first. Drain and flush the cleaner and water mixture out of the engine, remember to pull the block plugs to get all the sand, rocks and other debris out of the water galleys. Install new seal washers and anti-seize on the block plugs. Torque to 25 ft/lbs., be careful not to strip the block. Use just enough antifreeze for the freeze protection needed, use distilled water to reduce mineral scaling.

I have never found the burping process very effective in getting the air out of the system. Air pockets are common after a cooling system service. I’ve released large belches of air after filling the overflow tank, then running up to operating temp with the system open. The gauge read cool because it was reading and pumping air, yet the level looked OK. Remove the water temp sensor located in the cooling crossover manifold at the front of the engine. Fill the system from here and reinstall the sensor. Remove the radiator end of the vent hose until you get a small stream. This is the highest point in the coolant system, and will get rid of the air bubble. My car runs MUCH cooler when filling it this way. Start the car and watch the level.

Hope this helps.

 

Waterbridge thermostat seal was added circa 85 to 32V engines.

OP has an 80 so this seal does not apply.

From your description it sounds to me like a bad radiator or WP.

 

This sounds exactly like my 79 track car. Never comes close to moving above the lower white bar while driving around the track, if I sit in the pits too long the temp will start to climb.

I know for a fact it's the fan, just been too lazy to fix it (or install electric units).

 

Colin, the 84's 4.7 also have the seal, and I think the 83's as well. So you were right, circa 85.

 

A loose or worn out fan belt can also cause high idle temps. Have you checked it?

Dennis

 

Flow issues, either coolant or air, and air is what it is 90% of the time.

 

Had the same thing on my 86.5 Supra. Ran hot at idle or in town stop and go driving. Was fine on highway. Changed T-stat, coolant, belt, to no avail. Turned out to be radiator. Removed nearly 5 gallons of mayflies and mosquitoes. (I do a lot of driving around lakes.) Problem solved.

Good luck.

 

My vote is fan clutch. If it was a coolant flow problem, it would most probably overheat during driving as well.

Dan
'91 928GT S/C 475hp/460lb.ft