TheWall

My 89 S4 Auto runs warm(180 to 185 ) in cool weather (60's F) and has a new water pump and all fans are functional with the front flaps in the locked open position. I am considering putting In a new CSF aluminum radiator(current radiator appears to be original). I am wondering if it is worthwhile to keep the original radiator, in case as future owner wants to return the car all original? Currently the car has 42K miles and is in between a 2 to 3 Hagerty scale condition, closer to a 2.

FredR

Given the thermostat opens at 83C [181F] why would you think your car is running hotter than it should?

Rgds

Fred

TheWall

The engine temp actually gets up to 200 range in normal city driving. Maybe I should wait until the weather warms up, and see how the car handles a moderate hill climb in the heat. If it creeps up to 210 degrees, then try swapping out the radiator(?).

worf928

The 99-out-100 failure mode for a radiator on a 928 is that it leaks not that it 'stops cooling.'
A radiator has no active components. It does need liquid and air flow through it to work though.

So far, none of the data you provide point to an issue. 5-speeds want to run at 196 while autos run a few degrees hotter due to the need to cool the ATF combined with the cooler placement and lower average engine RPM resulting in less coolant flow.

Make sure though, that both of you fans work.

High than normal temps in city traffic is typically an air flow issue.

FredR

Whereabouts relative to the last white line on the temp gauge does the needle sit on the dash mounted temperature indicator?

Before you start thinking about radiator replacement plenty of things to consider. Main thing is the radiator should be clean inside and out. Very easy to get crap caught between the radiator and the a/c condensor.

You appear to be very specific about temperature numbers- where did you get them from? Remember coolant does not boil until about 220F or so and that is at atmospheric pressure. At the pressure of the coolant tank cap [15 psig] it is somewhere in the 230 to 240F range as I remember.

As the thermostat opens at 181F stands to reason that the operating temeprature will be higher than that. In hot climates the 928 cooling system is a bit challenged but can be made to work OK [ask me how I know].

Rgds

Fred

the flyin' scotsman

small typo

NC928S4

Try cleaning out the fins of the radiator. I had lots of crude wedged between oil/transmission cooler and assorted stuff blocking airflow that reduced cooling capacity.

Are your fans working correctly? How about the front flaps? Mine lost their mind and were opening and closing incessantly so I disconnected them in open position.

Mrmerlin

how are you determining the running temperature of your car?
Next time it runs hot quick stop and look to see if the flaps are closed.
It could be a good idea to pull the flap fuse when they are open.
when was the last time the thermo seals were replaced?
if its been a while since the system was inspected it would be wise to replace,
the thermostat the o ring and rear seal,
the coolant bottle cap,
the heater control valve and short hose,
if the coolant is older than 4 years then,
2 gallons of fresh coolant and 2 gallons of distilled water.
Had a customer with an engine that would operate at normal temps,
and then run hot when he drove up in the mountains,
and virtually the whole cooling system was replaced ,
radiator, pump, thermo and seals and cap and fan switch.
No changes, the next thing was going to be the headgaskets,
as thats the last thing that will control cooling system performance.
He found another good running engine
We swapped it in and the issues went away.

FredR

Yup.

Everytime the colonials use Brtiish units I have to get the calculator out to understand the number. The 928 was designed in SI units so better to stick to them!

Rgds

Fred

dr bob

In my limited experience with the same car and the same issue, I recommend that you replace the thermostat as your next step. For a long time I was in denial about thermostats failing. I was in SoCal and the car was OK in most situations and conditions. Most. After a bunch of other casual work, I finally replaced the thermostat. Suddenly I had temp regulation and no overheating at all on hot days "at speed", where previously it would sneak up towards the 210º line on the dash gauge.

I had previously (15+ years prior) put in a 175º thermostat as part of its first service in my care. So over the years the car had always run a little cool, just north of the 170º mark as one would expect except under the most extreme conditions. Even then it was only a needle-width above its normal spot on the gauge. The latest replacement is [the correct] 185º, so the gauge always reads a little hotter than before. But.... The fans cycle a lot less, engine warms a lot faster, the heater works (a plus in our new central Oregon climate), and the needle just about never moves at all once warmed up. All for an inexpensive thermostat.

Perhaps your results will be as good as mine.

XS29L9B

180*-185* is not hot.

TheWall

Thanks to all for the great information! My car ran hot from when I purchased it in 2015. One fan required new wiring, and fans now operate correctly. The front flaps are locked in open position. New thermostat was placed ( in the correct orientation ). The water pump had been replaced at a Porsche dealership a few months prior to my ownership. The car overheated in 80 degree weather prompting me to have the water pump removed and inspected, and it was beginning to fail ( impeller migration). Since water pump replaced, car has not overheated. Recently had new intake manifold gasket placed along with new fuel injector gaskets ( all were in poor condition, large air leak in intake system) Car still runs between 185-190 (readings by the dash guage). Is this a normal running temp in city traffic? Exterior of radiator is free of debris.
Radiator appears to be original to the car, is there any way to know if the water flow is compromised within the structure of the radiator? I suppose I could drive through the winter, and see the overheating becomes an issue when warmer weather returns. I am planning to drive the car from L.A. to San Fran sometime in next few months, and want to be sure the engine temps are normal before taking a long trip.

FredR

Can you define what you mean by "overheated". Did you get a full blown alarm on the annunciator?

When the thermostat was replaced did they also replace the rear seal?

As I requested earlier, when you were in the overheating scenario where was the needle in relation to the last white line on the display? The gauge display reading is not an absolute measure but a useful starting point of reference.

Rgds

Fred

TheWall

When the car overheated, The dash gauge was just touching the Red area, and it backed down just below red line when I ran the heater at maximum level. I was able to keep driving to the repair shop where I was headed
I can't tell by the work invoice if the rear seal was replaced. The thermostat was tested and found to be functioning properly, not replaced.

FredR

Fair enough- a stock system in our heat [44C in summer] can go to the redline when pushed hard- not a comfortable feeling for sure.

If the rear seal is not functioning corrrectly the water does not flow through the radiator as it should. My first 928 [a 90 S4] had a rear seal in an appalling condition giving cooling issues- new rear seal rectified that one. Visual inspection should reveal the truth but then if it was checked by someone reputable I doubt they would have missed that one but...?

Running the heater at max does remove some heat from the coolant. Sounds as though a bit more investigation is required to find out what is going on. Plenty of experitise available in your neighborhood assuming you are LA based.

Rgds

Fred