'87 911 pings when hot

My recently acquired '87 911 pings like crazy when the oil temp is within about 1/4"of the red zone. The DME is supposed to control the timing based on the input from various sensors. I assume one of the sensors
or the DME has failed - how do I determine which one has failed.
Additional info 11/1/99:
33K miles (verified by Carfax.com)
Pings when temp is 106 doesn't when hi 80's
oil temp normal when temp is hi 80's lo 90's
Suspected lo octane gas from PO - ran almost MT & refilled w/Chevron Supreme -no effect


[This message has been edited by Charlie Moore (edited 11-01-1999).]

1/4" of red zone is about 265'-270' which is too hot you probably are having detonation (pinging)as a result

Yes, the DME does control timing, but only to a point. In other words, I think it will retard timing to try to stop detonation or pre-ignition, but there is a limit as to how far it will retard the timing. For example, if the engine is way too hot, or if you used fuel that had octane that was way, way too low, the DME may not be able to retard timing enough to stop the pinging.

If your car is "pinging like crazy" you really should get it fixed ASAP, as it is giving you a clear audible warning that it is about to put a hole in a piston, break rings, etc.!

Brian

I think the real question here is why your oil temperature is so high. You should be paranoid about that. Once the temperature gauge reaches the second mark, the oil temperature is at 194 degrees, which is warm enough to open the thermostat to allow the oil to flow to the front fender oil cooler (passenger side front wheel well). You should feel the oil lines that run up to the cooler and see if they are warm to the touch. If they are not, then you need a new thermostat. If they are hot, the thermostat is okay. There is on the 87-89 Carrera a fan on the front oil cooler which is supposed to turn on when the oil reaches 250 degrees (third mark on the gauge, which is about 248 degrees). This fan will reduce the oil temperature; your fan may not be operating because it's broken or the thermal switch is not operating. You should have that checked out too. It's possible to put a different thermal switch on there; I had a 235 degree switch put on my 88 Carrera.

There are some reasons why your oil temperatures are so high; there could be a lot of dirt on the cylinder cooling fins. There could be dirt (or even undercoating) on the oil lines to the front cooler, which will not help things. Or, if the car has been rebuilt, the cooling fins on the cylinder heads could be installed upside down, which would inhibit cooling. Or, you could have a bad internal problem which is heating your oil.

The consensus is not to run the engine with oil temperatures over 250 degrees (third mark on the gauge). You should run synthetic oil (Mobil 1) which will protect better at higher temperatures, but you should also try to figure out why the temperatures are so high. If it's pinging, look out!

My 88 Carrera never ran over about 235 degrees even in stop and go highway traffic with the air on in Tampa, Florida, on a 95 degree day. Usually it hung right on the first mark on the gauge. I would be alarmed at your oil temperatures, and get it checked out asap.

Vic
87 930

VJD3:
Thanks for the thoughtful suggestions.
The oil is getting to the front oil cooler- I burned my hand trying to see if the fan was blowing air thru it. It wasn't because it's not hooked up. I found a cable in the trunk which seems to go to the fan but doesn't connect to anything in the trunk - is blue wire + brown wire small white connector with male pins. I've searched the trunk for a cable with a mating connector -can't find. Tracing this cable to the O/C the blue wire is loose with a round black plastic blivet on the dangling end - I assume this is/was one of the fan terminals?
I'm a little confused about the fan operation -in Bruce Anderson's book he states
that the proper operating temp for a 911 is 180 -220 but the fan thermostat doesn't switch the fan on until 244 degrees -seems like it should switch on sooner.
I saw another posting where someone installed a switch in the rear wiper place on the dash to manually override the thermostat - sounds like a trick idea.
The overheating/pinging has gone away now that the temp is hi 80's (was 106 when I saw the problem). I still suspect the DME or one of the sensors is malfunctioning when it's hot out and will need to resolve before next summer as normal temp midsummer is 115-120.
My last 911, an '85 Euro car never ran hot or pinged ever down here so there is something definitely wrong with this one.
Charlie

[This message has been edited by Charlie Moore (edited 11-01-1999).]

The electric fan is a strange thing, its true that it does not kick on until about 245 degrees, which is pretty hot! It apparently is really just an emergency device, not really intended to go on during normal driving.

I think it would be nice to find a lower temperature sender to make it switch on at about 220 or so. Don't know if this exists, though I would suspect that it is a fairly standard type sender, and a lower temp unit could be found with some searching.

I have an 87 and never liked the temp at which the fender cooler fan started so I hooked up a switch to override the thermo switch and wired it through a dash mounted switch. Works fine. I like cool oil. Sounds to me that you are not getting much cooling out of your engine mounted cooler if the oil is very hot in the line to the front cooler. You should be able to get your hand at the air discharge side of the cooler and check out the temperature there. You can also connect a timing light and see what the ignition timing is set at. If your timing is fine, get after the coolers! Ned

I did not like the thermostat setting, so I rooted around at my local independent foreign car parts store and found one that came from a Mercedes. It had the right threads and was set at 100C/212F.

My engine normally runs at 180-200, only getting higher when racing. This upgrade cured my problem with hot oil...