I recently purchased a factory oil temp gauge for my 88 240. I made a sending unit at work by drill & tapping an oil plug and threading a sender in. I tested the sender with the gauge with a heat gun and was able to read up to 300 degrees.

I installed the gauge in my car earlier this week and now have concerns about my oil temp being unusually low. At first, I thought it was just not getting warmed up enough on short in-town drives, but I went on a 90 mile highway drive today and the temp stayed near 120 degrees on the highway. When I would stop and sit at idle, the temp would creep up to 150-160 degrees, but go right back down to 120 (130 max) when cruising. Does this seem right? For the record, the ambient temperature here is about 30 degrees right now, is it possible the oil pan was cooling down to quickly at highway speeds to get an accurate reading? Also, the coolant temp gauge was staying at about 1/3 the whole drive.

Maybe these readings are normal for a N/A engine, I was just anticipating the temp to hover between 170-200 at highway speeds. I am not overly concerned, except I am worried that contaminates are not burning out of the oil as they should.

 

is the sender deep enough into the oil pan that its not being overly influenced by the outside temperature?

I've only had 2 cars with an oil temperature gauge that I can remember.

1) 1989 VW Jetta GLI had oil temp on the diigtal multifunction display (one thing at a time, how annoying)... driving hard in hot weather, the oil would frequently get up around 220F after an extended period.

2) 1971 VW Transporter (microbus). camper. original 1600cc carburetor engine. aftermarket oil temp gauge. if the oil temp started climbing above 200F, it was time to downshift into 3rd and slow down 15-25 mph. 40-45 on grades instead of 65-70. that engine was quite happy with 180F indicated oil temp.

I would imagine you would have to thrash a 240 pretty hard to get its oil temp high.

 

The more I thought about it, the more I agree with you that you would have to really beat a 240 up to get the oil temp high...maybe that's why the oil temp gauge was such a rare option, as it's really probably not that necessary. The sender is recessed into the drain plug and is actually protruding into the pan slightly further than the factory sender.

I may end up pulling the gauge and filling it with an ambient temp gauge if I ever locate one ...Maybe i'll just save it for my b230ft build in my 242... It is rather boring in my N/A 245 ha ha.

ps. I bet that 71' transporter was a blast