tosha

Hi folks, I drive about an hour from SF to the South Bay on the scenic 280. Even when I'm not in the colder part of the highway, I've noticed my temperature rising and falling from about the 1/3 mark down to about 1/6th. I've always wondered if it's okay for my oil temperature to drop so much during a drive. Could a thermostat be failing? It's about 55-65ºF here.

Here's a photo of the indicator level when it drops to about 1/6.

jstyer

Normal. That's the thermostat working, not failing.

993Maineiac

Nice and cool. Mine usually runs in the middle of the range on the road.

tosha

What's strange to me is that it modulates significantly. The engine seems to run better when it gets to the 1/3rd mark, and it stays there typically when I'm driving around town.

My Carrera 3.2's oil temperature doesn't change much during drives, unlike the 993, so I thought I'd ask.

993Maineiac

They do move quite a bit in city and stop and go driving.

tosha

911F1

Check to see if the ballist resistor for your oil cooler fan is working. If its not, the fan will only run on high when oil temp increases.
It could be bouncing off of this cycle. Giving you a swing in temps that you noticed. Take a look at the link below.
https://www.bergvillfx.com/fanresistor

spruden

tosha

911F1

No problem. I used this method to test both of my fans. Tore writes "pop off the relay housing with a sharp knife, reinsert the relay, and press twe two relays inside with your finger to run the fans."

mpruden

I think you've misunderstood some of the folks trying to help you. Based on your initial post, I agree that the needle drop you see is just that, your thermostat opening, letting a rush of unheated oil into your engine. Every 993 I've ever driven does the exact same thing. At the ambient temp you mention, my car does this every time.

Does the temperature eventually level out at the thermostat point (meaning there is no more "cool" oil in the system, as the thermostat is letting enough warm oil through the cooler to keep it roughly at temperature)? If so, I'd say your system is working normally.


Not trying to troll, just trying to help.

Tore's excellent documentation on site goes over this in a lot of detail.

tosha

Thanks, it's helpful to understand that there's cold oil in the system that will cause temperature fluctuations for some time after the start of the drive. I don't recall the temperature stabilizing. It's possible that even though my commute is an hour long, the unheated oil is always cold enough to cause engine oil temperature to drop. Ambient temperature on the drive is usually 55-70ºF.

mpruden

Going from memory here, but after a couple dips, it should stabilize. The first dip will be the most noticeable, the next will be smaller. After that, it should be smooth unless you're going through some strange environmental circumstances.

71-3.0-911

When my ballast resistor failed, the temp had to climb significantly (way too high, but never in the red) for the fan to kick on. I only realized this in stop and go traffic. I now have the ballast replaced and a manual fan override switch installed. Guess I'm paranoid about the temp getting too hot now.

Point is, if your ballast resistor has failed, the symptoms are far different than what the OP is experiencing.

TMc993

FWIW, I live in northern Georgia where the summers can get pretty hot and the winters pretty cold. My 993 ran at consistently similar oil temps in both hot and cold weather, but in the spring and the fall, when temps hovered in the 50-55 degree range, I saw exactly the same oils temp swings that you are seeing. Like you, I was concerned the first couple of times I saw it, and did confirm that my ballast resistors were good, but I grew accustomed to it over 11 years of ownership and it never seemed to affect the way the car ran.