928 overheat at idle
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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 gauge 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?
__________________
Ed Sanders
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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.
__________________
Andy
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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.
__________________
Jim Mayzurk
93 GTS 5-spd