flyrade

My 89 928 S4 temp gauge stays withing the normal operating range, but gets very close to the high side when running the a/c. The fans come on and the radiator appears to be clean with plenty of fluid.

Is this high side reading normal?
Is there anything I can do to improve the cooling efficiency - such as change the radiator fluid, clean the radiator inlets, etc?

MFranke

Mine ride lower or middle in the band usually. This is with new coolant, thermostat, and clear airflow. Leaves and stuff can get behind the condenser.

Bilal928S4

Water wetter additive helps.

Dictys

You need to measure the actual coolant temp with a IR gun or from one of the ECU via a tester or ST unit.

More than often the gauge does not accurately reflect the real coolant temp.

My 1990 S4 runs between 86.5c and 89c whatever the outside weather or fans, a/c is doing and it maintains that temp at idle in traffic or at vmax.

kevinlieb

Check that your flaps are opening as well. That makes a big difference.

Koenig-Specials 928

This was happening to me at the end of summer. Everything was indicating that all was well i.e fans came on etc but operating more on the hot side. It troubled me a bit until one day I decided to actually watch the fans and realized that they were running slower than normal. The 20+ year old fans were seizing up. I replaced them with the Ford Contour units and temp gauge immediately back to the middle of the gauge. Check your fans even though they are running. Are they running fast enough? Mine weren't. Hope this helps!

Mrmerlin

has the thermostat been replaced recently?
was the rear thermostat seal also replaced?
was the coolant bottle cap also replaced>?
these things can make the car run hotter if they are old also swap in a new heater control valve and short hose if you working on the thermostat

newbie9280

most of these radiators are over 20 years old... if any of the previous owners ever used tap water instead of distilled water then there might be scaling on the inside of the radiator..... most german cars of this age perform better cooling wise with a new radiator..... it is an expensive option but I garantee it will cool better than an original radiator that is 20 years old with calcium and other deposits on the inside.... its plain science.

GregBBRD

You need to explain "high side" a bit better, for it to mean much, to me.

Here's how they should work, in "warm" weather:

The 3/4 mark is 210 degrees. "Normal" running is about 2 needle widths below this mark. This is when the fans come on. It should 'cool" back down to about 3 needle widths above halfway and the fans should turn off.

In "cold weather, with the flaps open:

The air rushing past the engine generally cools the block and the coolant so that the thermostat never opens. It is not uncommon for them to run below the 1/2 mark at freeway speeds. When sitting still, the thermostat may open, but the fans may not come on. This is generally about 1/8" above the halfway mark.

Generally:

If both fans come on at "low speed", run for a couple of minutes, and then turn off, everything is fine.

If the fans come on and will not cycle (turn off) then you need to look at your thermostat, seal behind the thermostat, radiator condition, etc.

You should not have the fans "switch" to high speed mode, unless the outside temperature is over 100 degrees and you are sitting in traffic with the A/C on. If high speed does switch on, you should be able to see the temperature gauge start dropping within 15-20 seconds.

Hope that helps!

Whitesands

Pic of mine about 5yrs ago, radiator is old and has had one end tank replaced by PO.

Outside temp was 95ish, A/C on, I had been on the interstate for about 45 minutes.

Today, it's still much the same on a hot day, it will go about one needle width higher in stop and start traffic but that's about it.

IcemanG17

lots of variables here.....

the single biggest is how old is your radiator....adding to that...how often has its coolant been changed....radiators in 928's work really well IF they are 100%....even slightly clogged radiators cause all kinds of issues....everyone assumes theirs is fine...but have you tested it...

I had a 3 year old radiator flush out LOTS AND LOTS of rust from a 928....imagine what a 20+ year old radiator would do.....

1st thing to do...pull the radiator (super easy) and take it to a radiator shop for a professional cleaning-test....money well spent....

flyrade

First of all - thanks to all of you for your replies and great advise. I certainly appreciate it.

After reading all the above, here is my plan. First I'm going to have the system flushed and the coolant replaced with the Xerox G05 mentioned above. I found it at a NAPA store for $16 a gallon and got two gallons since the system requires 16 ltrs. I also got two gallons of distilled water from Walmart for about $0.70 a gallon. I also ordered a new 75 C thermostat.

I would hope this will cure the problem, but if not the next step will be to take the radiator to a pro and have him look at it, clean it, etc.

I'll let you know how all this turns out. Thanks again for all your help.

Tom. M

The 89 and up digital dash has a different temp gauge than that pictured above. My GT runs about 3 or so needle widths below the 100 C line (white line on the right) around here (usually cool year round).

On the trip to Wichita this past summer, the outside temps were 100 plus and we were running the A/C non-stop. I was consistently at or a needle width above the 100C line....and was a bit worried when I queried other 928ers in our group. Most with digital dashes (90GT, some GTS etc) all were running at or just below the 100C line. Best I could figure was that the 89 was the only one of the bunch that had both the digital dash and oil cooler in the end tank of the rad. All the others had air cooled oil coolers...so that additional loading (heat from the oil) was likely the cause of my extra high temps...

BTW..running over 6000 miles like that had no ill effects at all...ran perfectly there and back with A/C nearly on the whole time.

flyrade

After reading all your advise above, I just had the radiator flushed out, and the fluid replaced with the Zerex G05 and distilled water. The 83C degree thermostat was also replaced with a 75C.
There are two horizontal air intake slits in the front of the car, and if you reach into the upper portion of the top slit you will find a plastic piece that I guess is used to guide the air to the radiator. It seems part of that plastic piece slipped down into the air stream, therefore blocking some of the air getting to the radiator. All I had to do was push it up into place, and it snapped into position. Now I'll make that part of my routine maintenance check.
On the very bottom of the air intake there is also another plastic piece, again I would assume to guide the air to the radiator. Mine is cracked, making it difficult to keep in position. I will continue to monitor that as well, and remove it if it becomes a further problem.
I did not replace the radiator cap, but will in the near future.
However, the good news is, after several test runs, the temp gauge is down in the middle of the normal operating range. So all this worked.
Thanks again to all who helped. I hope I can to the same for you some day.

GregBBRD

Everything is good, except your choice of thermostat. Put the stock 83 degree thermostat in (get a new one).