If I start the engine and hold it at a fast idle, like 1500-2000 RPM, the coolant temp gauge starts to rise within a couple minutes. But even if I run the engine for 5-10 minutes, I see no rise on the oil temp gauge. I fully expected the oil temp to rise slower than the coolant, but I didn't see it rise at all in that 5-10 minutes. Am I not giving it enough time to heat the oil? Is it even possible to see much of an oil temp rise when it's just running in the garage and not being driven under load?

I have both brand new coolant and oil temp sensors installed (thank you Eric) and I've double checked the part numbers to make sure I didn't get them swapped. I checked the oil temp sensor resistance and it's around 2500 ohms cold. I haven't measured it hot yet. (Nor do I have a laser thermometer by which to check the oil pan temp.) Also, I verified continuity in the wiring. With the ignition ON, I can tap ground the end of the wire and the gauge rises smartly.

Is this a case where I will just have to get the car out on the road before I can see the oil temp rise?
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Previous owner of my 1800e claimed the sender/gauge for oil temp not working. Turned out it was working fine. As been stated the oil temp doesn’t show very often. In my experience, higher ambient temps 80-85 F and harder driving, will result in some movement of the needle.

Thanks for the additional confirmation.

It's starting to make me wonder why the car even has an oil temp gauge in the first place.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Chris wrote -- "Is this a case where I will just have to get the car out on the road before I can see the oil temp rise?" Simple answer--yes. I had an 1800S on the road years ago and I don't recall if the oil temp gauge worked--but I can give you an example of having one in an air cooled VW Microbus. It took a good 15-20 minutes of driving on the highway before the needle started to move from its 140 degree (F) minimum. -- Dave

OK, Dave. That's good info. I didn't think about the lower limit of the gauge scale being 140F. Actually the gauge doesn't have numbers - just "C" at the low end and "H" at the high end. But if "C" = ~140F then I could see where it would take a while to even start to register. The garage, along with the engine oil, was probably around 65F before I fired it up.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Chris;

I agree with Dave...oil temp takes a loooong time to come up...and even longer in the garage under no load! I just checked The Green Book for the '71E and it does not have specs for the Oil Temp Sensor resistance (like the nice R vs Temp graphs they have for the D-Jet sensors) ...but if you're that concerned (or even just interested), remove Sensor (plug hole in Sump!), and place it into a cup of boiling water (don't forget to supply a gnd to case of Sensor, and with Ign ON, note where Gauge shows (I'd mark that indication as a calibrated reference point)...and don't be afraid if needle approaches that level during extended highway runs...

Cheers

Ron,

That's a good test. I considered taking a heat gun to the oil pan but figured all that would get me was a bunch of scorched paint. Based on what you and Dave are saying, I think I'll postpone worrying about it until I can actually take it out for a long enough drive.

During the same engine run the coolant temp actually touched the red zone. I think that may have been due to a low coolant level. (After cool-down the expansion bottle was completely empty.) I do know that the thermostat opened as the upper radiator hose got hot. I added coolant and squeezed some air out of the upper hose so I'm hoping that after a couple more heat up/cool down cycles, and adding coolant as required, that the temp will run normal. If all things are working as they should, do you know approximately where the coolant temp needle would normally run?
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Chris; Normal temp indication would be in the center region of indicator somewhere, but it varies with each car, and with Tstat installed obviously...best is to calibrate gauge by sensing boiling water with Sensor as a test, and marking this on gauge...then, there's no doubt!
...but FIRST, if Exp Bottle is empty, you don't know how low Cooling Sys is, so open and fill Rad!...with Coolant mix, not water only! See: http://www.sw-em.com/Cooling_System.htm#filling_cooling_system

Dave; Filled thermal sys indicator has no damping and is virtually instantly responding, so Tstat action is visible...Electrical Gauge of '73, is supplied by Voltage Stabilizer, and has a long time constant so responds slower than growing a California Redwood...

Cheers

"...so open and fill Rad!...with Coolant mix, not water only!..."

No worries there. I'm rather attentive in that area.

Thanks for the info!

What you are describing regarding the coolant temp may be caused by low coolant -- but it's very typical of B18/20 behavior - especially with the older very sensitive capillary tube type gauge - to see the coolant temp go high until the thermostat opens. You did right by "burping" the cooling system but if it's safe to reach the bottom radiator hose (watch those fingers near the fan), that one will be most effective -- as well as holding the expansion tank up above the motor and heating system. -- Dave

The heater valve does sit on pretty high ground in these things.

Thanks!

Historically there have been many threads asking this same question. Fact is, the oil temperature is well controlled and low indicated temps are normal. Remember that the oil is also a coolant and that fact is just as important as it being a lubricant,
You might have to cruise across Death Valley at 100mph to get the gauge up near the top and it will still be nothing to worry about.
With the 1800 Volvo were worried about cooling, hence the oil "cooler", that definition is debatable, and the fact that at the time of introduction, multi grade oils were in their infancy. Bottom line, don't worry about it. Change the oil and filter regularly and keep it up to the mark.

Thanks, Derek.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Chris--when I wrote 140 degrees (F) -- I was referring to the aftermarket gauge I'd installed in the VW. But the parallel is the same--it takes quite a bit longer to warm the oil than the coolant - why some race cars have the oil pre-heated before going into competition. -- Dave