Low oil temp reading. Any ideas?

[KS]

Although I have not pushed the engine under any load or at high revs while it's still fresh, I can't help wondering about the oil temperature reading seeming very low, even when running on the rolling road during ECU set-up.

The gauge is in Centigrade, with figures marked at 30, 80, 100, 120 and 170 degrees. Date-stamped 12/69 and from a 911S. The temperature sender is a genuine Bosch, part number 901.641.632.00.

On start-up, the gauge goes to 30 (effectively 'zero' at this point, buy the lowest the gauge will read) and as the engine warms up, it reaches just over midway between the 30°C and 80°C marks (approx 60° if it's vaguely linear) and then stays there, not rising or falling. The ambient temperature here right now is about 15°C at best.

I have checked the gauge by 'flashing' the sender lead to earth, at which point the gauge goes to maximum. I have also checked the sender as best I can with an ohmmeter in boiling water. The resistance falls as the temperature rises roughly in line with figures found on PP. Using a temperature gun, the surface reading of the sender is not a million miles off the gauge reading with the engine running.

I began to wonder if the thermostat was jammed open, but this morning I removed it and, again using a can of boiling water on the stove (just as well Sarah's at work...), the 'stat began to open when the body reached 80°C, opened fully before 100°C, and then closed off again when I ran it under cold water. So, it looks like it's working OK.

I am at a loss. The engine currently has just the stock cooler – I'll run a front-mounted one if it proves necessary, but at the moment, high oil temps look the least of my worries.

Is there an obvious point I'm overlooking, or is this simply a case of the ambient temperature being relatively low? I'd still expect the temp gauge to read higher than 60°C, or thereabouts, though.

[redrobin911]

Keith - even my race car engine runs cool (according to the gauge) - for peace of mind borrow a laser temperature gun/gauge and get a temperature readings from the engine to see if it matches your gauge wouldn't be surprised if not pretty close.

[haasad]

Keith your oil should be at about 80/90 degrees max c so the stat is ok. Sender to gauge should be matched. Try pointing an infrared thermometer if you have one at the oil return line or even when its really warmed up a bulb type thermometer in the tank would be close. None of this indication is actually calibrated so I would get to know what you really have before worrying. 60 degrees is too cold to drive off moisture so it should be running a bit hotter in my view.

[KS]

There are just two sender types and mine is the correct one for that year gauge. I did point the temp gun at the oil lines and they did appear to read higher – I beginning to think it's the gauge that's at fault. Trouble is, I don't have one to replace it with and don't really feel like buying a whole new combination instrument unless I really have to, especially as the current one has been cosmetically refurbed.

Does anyone have a pre-74 oil temp gauge module I can use in my current instrument?