Temp cools down when driving

[iso_hi]

My m42's temperature stays right in the middle on idle but recently I started noticing that when I'm on the highway the temperature almost goes to the 1/4th mark.

It was running fine since I replaced the oil filter housing gasket a few months ago and recently started noticing my temperature being lower then usual. That has been leading to subpar mileage.

Anyone have an idea what might be going on?

[ccsdo5]

Thermostat is stuck open I bet.

[bmwman91]

Yup, sounds like a thermostat issue.

When you replace it, make sure to get the head and tstat housing immaculately clean before installing the new gasket. Also make sure that the small bypass groove in the housing (connects the 2 chambers) is clean and clear. Having that channel open makes bleeding the coolant system a breeze (versus a big pain in the ass if it is blocked).

[iso_hi]

That's what I was assuming, hopefully my local shop can have the thermostat/gasket for me by noon since I'll be driving to Oregon late Monday.

I'll report back.

[gearheadE30]

Yep, same thing happened to me when my tstat broke one of the little support arms.

[iso_hi]

Just swapped out the thermostat, all is good once again.

Thank you all for the help.