Old & New

In moderate weather (below 80F here since last fall) I have seen my 89 return radiator hose run ~210F according to the IR thermometer. This is when the car is parked / idling and the temp gauge is at the upper white line. Gauge sits in middle when driving; hoses are at thermostat temperature at that point.

What have you measured (with either an infra-red or accurate contact thermometer), and under what conditions? Maybe shed some light on this gauge accuracy mystery...

Chris

OK, its mid 70's here today.

One needle width below the upper white line and my temp reading on the return hose was 163F.

Chris

Tom. M

Don't forget..we are talking about two different guage styles..(unless Chris was driving the 91 ;-) ).

My 89 GT would sit about 1 or 2 needle widths below the upper white line (to the right). In traffic on a warm day..70 or higher...it sits at about the line. Not much fluctuation. I have never seen it in the middle of the gauge..always at or near the right side when fully warmed up..

My 87 that had the gauge on the left...rose to just above the lower bar in normal driving..while sitting in traffic...would go up to the middle..until traffic cleared..and then drop down again..

163F sounds pretty good ..if not a little cool?...

Later,
Tom

P.S. Hope to utilize Chris' IR temp checker...at the Track Attack this weekend for actual comparison.

SharkSkin

I just checked this over the weekend. I zip-tied a thermocouple to the upper hose and stuck a piece of cardboard between the AC condensor and the radiator... I was checking my thermal switch for the fan and the car simply wouldn't get hot enough to activate the switch without some "help". My guage needle normally rests dead center between the two white marks while driving. This seems to be about 165ºF actual temp. I have seen it approach the 2nd white mark in traffic on an 80º day. The second white mark is about 180ºF. My fan came on at about 98ºC, ~205ºF, which was about one needle-width below the red area.

I'm betting that as answers come back you will find that the guages have to be evaluated on a per-car basis, using actual measurements... with variations in the gauges themselves, senders and wiring they're probably all over the place.

Doug Hillary

Hi,

during the last 12 months I have monitored my engine's temperatures taking about seventy IR readings on the way
The monitoring was done to enable some answers to questions raised on RENNLIST over oils and the 928's cooling capacity

They are given below in this order - average, highest, lowest

Gauge reading: 84, 87, 81
Thermostat housing: 85, 88, 78
Rad hose top: 72, 88, 55
Rad hose bot: 77, 90, 67
Valve covers: 88, 94, 85
Vee: 88, 94, 80
Oil cooler top: 74, 88, 55
Oil cooler bot: 76, 90, 59
Ambient: 23, 34, -2

All +/- 2C

Note:
a) The "live" gauge reading is really an indication only and is not clinically accurate

b) The OEM thermostat cracks at 83C and is fully open at 98C

c) The bottom hose can be warmer than the top hose due to the integrated oil cooler and the cooling system's "heat sink" radiator

NOTE: the "heat sink" style cooling system uses the radiator to shed heat even with a closed thermostat. In very cold climates the thermostat may rarely open! It may struggle at times to make the thermostat's 83C crack point in these cases especially considering the chill factor when moving

d) Reading at four points ( say top hose, bottom hose, OC top and bottom etc. ) will tell if the system still has reserve capacity when overheating is suspected

e) The vee & valve covers are a good indicator of the engine's actual "core" temp

f) It takes about 30 minutes to fully warm up a 928 at an ambient around 15C

g) Cold engines should not be revved too high as the OP relief valve cracks at 8 to 9 bar - a very high pressure. This particularly applies if you are using a 15w/20w-50 oil!

NOTE: I changed from a synthetic 15w-50 oil to a synthetic 5w-40 oil during this time and the only two measureing points that registered a consistent change were the top and bottom radiator hoses. They both reduced by about 1C

h) The 928's oil cooler thermostat 87C opening point suggests it operates as a late stage of heat management - this corresponds with the engine's "core" temp of 88-90C.

NOTE: Less engine wear occurs when the engine's core temperature is maintained above 80-83C

NOTE: Most engines without an oil cooler usually have a normal oil temperature 10-20C warmer that the coolant temp.

i) The S4's overheating warning systems has two alert points, 1 @ 118C and 2 @ 120C

Best of luck

Chris

Hey Doug, quick question, shouldn't the bottom rad hose be cooler than the top ??

Chris

Normy

My car stays at the lower bar...I have a GT radiator [no coolers] on my '85 S2 and a 75 degree thermostat. Also, I have rigged the AC fan to run continuously in concert with my engine-driven fan.

My temp gauge, on the left and vertical, will move just a shade above the bar in traffic on a 90 F/ 33 C day here in Orlando. Otherwise, it sits just below.

I've never put an IR temp sensor on the radiator. I can feel a definite difference in how the car runs on a 90 F day in July versus a 65 F day in January.....but it certainly is not overheating. I don't trust that guage in the least; I pay attention to trend. I'd have your car checked, and if it turned out to be running properly, then I'd pull the gauge cluster and remove/ glue the needle to a lower position so that it indicates in the middle in normal driving.

N!
'85 S2 5 Speed

Doug Hillary

Hi Chris,

many peculiarities exist regarding the 928's engine systems as you know

Firstly, all of my measurements were taken with the engine up to it's core operating temperature or beyond. At least 60kms (nearly 40miles) had been covered prior to obtaining any group of readings. Some measurements were taken with the engine running, some immediately after stopping and all at exactly the same measurement points. Only small variances occurred between each condition

Variances at the key points of the Vee and valve covers were/are very very small

The bottom hose was hotter on 47 occasions
The top hose was hotter on 16 occasions
Both were equal on 7 occasions
The median variance between top and bottom hoses is 2C

I think that the oil cooler's influence on the bottom hose is significant as the oil cooler is unlikely to be constantly open very often. Most oil coolers with thermostats opening around 90C cycle quite rapidly. This is especially noticeable on air-cooled engines

The best way for temperature measurement would be to use thermocouples linked to a PC with real time recording but that's not for me!

Again, the temperature gauge is purely a "live" temperature indicator. In my case it has averaged a reading 22% lower than the vee & valve covers. It is affected by aircon use (fans on) etc. etc. but core temperature is very stable! The cooling system's capacity is truely amazing!!!

Regards

Old & New

Doug,

Once again, above and beyond the call of duty!

Your data, and how my former 81 behaves leads me to believe that I have a cooling problem, not just a gauge problem. This existed before addition of the supercharger, and hasn't changed much since.

I have a new thermostat and rear seal, the fans turn on at the appropriate time and move a lot of air, the front flaps are lashed wide open, the radiator is clean inside and out (and new looking; replaced by the PO), but it just runs too warm unless the car is moving >25mph or I direct the garden hose onto the radiator.

I plan on double checking that the thermostat is seating properly against the rear seal. Besides possibly being due to a loose impeller on the water pump, I am out of ideas.

Doug Hillary

Hi Old & New,

your temps are only 9C higher than mine - not much! Do the four point IR temp check - you still have a lot of capacity!

Importantly the stock thermostat is not fully open until 98C(209F) and the first alert is at 118C so they (Porsche Engineers) must have been content for the motor to run in the 100-110> range quite often

These engine will shed heat very quickly once both the oil and coolant thermostats are fully open!

What oil and grade do you use and what hot idle oil pressure do you get?

Regards

Old & New

Doug,

More info on the four point check, please; I find that the radiator lowers the temp by ~15F (unless I spray it with the garden hose, of course).

My former 81 maintained its temperature so well that I was able to run it with the radiator cap loosened / no system pressure without boiling over. Another time I ran it without the cooling fan connected, and the temperature was stable enough for stop-and-go city traffic in 80F weather. I don't get the feeling that my 89 would tolerate those conditions as well!

I have been using Castrol GTX 20W-50, and I see 3 bar at idle.

Garth S

Old & New,
As you infered, with a clean cooling circuit on a well tuned engine, cooling problems on a S4 are frequently limited to the thermostat pellet, thermostat rear seal, water pump impeller loose, or the O - ring seal installed on the wrong side ( OK, so I added a couple ).
I'm sure your O - ring position and rear seal are perfect: A loose water pump impeller is bound to be dramatic - my pump bearing (S4) failed allowing the plastic impeller to kiss the block. The freewheeling impeller led to a flurry of alarms and a little boil over prior to shutdown, all in a great rush. I was left with the impression that a loose impeller was like pregnancy - there is no half way!
This leaves the pellet: Almost any problem I've ever had in cooling circuits of well maintained cars usually tracks back to that 1930's engineered wax - capsul activated immersion valve, aka 'thermostat'. They do all the usual, whether old or new ( pardon): they stick open, closed, cages fail , some are slow, never fully open, ....
The latter could be the problem here, not achieving a seal against the fresh rear seal.
Not trusting even new thermostats, I now always place a couple of them in a pot of cool water with a thermometer, slowly rise to the boil, and note opening ( and closing) behavior. They do not all pass the test - it may be worthwhile doing.

Doug Hillary

Hi Old & New,

see an earlier post re the four points item d) I think
Once the engine is fully warmed up (stable core temp), if any of the points are below 90C you still have significant capacity in reserve

Depending on your ambient temperature the oil you are using may need to be revisited see here;

http://www.landsharkoz.com/techtips.htm

Check under "Lubricants for the 928"

Regards

Jeff928S4

I'll add a "cooling" question into the mix.

Does the 928 have fans that run after the car is shut down? I've had my 89 S4 for like a week and the temp guage is always just below the third white line. In traffic, it sit right on the line, but never goes any higher.

When I shut the car down, no fans run. On my 944, I always had fans running after shut down. I dunno.

Jeff

Lagavulin

Doug, good info as usual!

Since you are able to lower the temp by using a garden hose on the radiator, have you checked to make sure that the front of the radiator is completely sealed so that the incoming air from the grill opening is forced through the radiator, versus 'leaking' around it and not carrying heat away?