Strange engine temperature behavior at idle

[Huskymaniac]

I thought my mechanic may be under-filling my cars when doing ATF changes. Both my Subaru SVX and Tribeca got partial drain and re-fills.

When warm, the SVX stick is reading about 20% between the warm L and F markers. The Tribeca is mid-way between the cold F and warm L. So that seems way too low whereas the SVX is just a little low. On the Tribeca I notice that the brake pedal vibrates a little when it is cold and I put it in reverse. Could they be related and how bad is this in terms of damage that could have been done. When warm, I notice no vibrations so I assume the fluid is expanding so a sufficient volume.

I checked the SVX levels because I was concerned once I saw the Tribeca levels. I wanted to make sure the transmission temps were high enough so I was monitoring the OBD live data. I couldn't get transmission temp but I got engine temps. I noticed something odd while monitoring this. The car was running at 203F after a 10 mile drive around town. It took a long time for it to drop to 201F. I decided to turn up the heater to get it to cool down faster. I was curious to see at what temperature the fans turned off. When I did this the temperature rose!!! It went up to about 204F and I then turned off the heater. The temp quickly dropped to 201F. I then decided to see what effect revving the engine would have. It was idling at 600 RPM and I went up to 1200 RPM. The temperature quickly dropped to 199F. The outside temp was about 50F and the cabin temp was about 70F. Does this sound normal? Maybe my heater was doing less cooling of the coolant than the radiator?

 

[[RT] ProjUltraZ]

is your engine running when you check the ATF dipstick? you could top up to the level you want.

about the 600 vs 1200 rpm, it's probably your water pump moving coolant faster w/ rpm

 

[Huskymaniac]

Yes, the engine was running and the gear selector was in park.

The RPM thing I get but what really surprised me was that the engine temp went up when I turned on the heater.

 

[The_Jeff]

If your coolant temp sensor is on the opposite side of your head/block compared to your thermostat you'll see this.

The thermostat was closing off because you were losing heat to the heater, which is not part of the radiator side of the thermostat. So on the opposite end of your motor, the coolant had spent more time travelling more slowly, and had picked up more heat.

I had this on an old dodge spirit, the gauge would go DOWN when I was climbing a hill or otherwise flogging it.

Over-analysis like this is why the new temp gauges are so computer-dampened.

As for your ATF, they say better on the low side than overfill, because of foaming. For the vibration you probably have a motor mount that's not as soft as it used to be.

 

[Huskymaniac]

Very informative. Thanks.

 

[Huskymaniac]

Follow up:

The vibration was due to low ATF. We added just a little and the vibration, when cold, went away.

I still wish my engine ran a little cooler and I am thinking of running a lower temp thermostat. I don't think mine is fully open until the coolant reaches almost 195F.

 

[mcrn]

whats wrong with those temps?

 

[bullwinkle]

You'll get better MPGs and less moisture/condensation in your oil if you stick with the 195F 'stat.