350SDL temperature - PeachParts Mercedes-Benz Forum

DieselPaul · #1 08-12-2011, 04:03 PM

So I just bought a 1991 350SDL. The AC did not work when I got it, but there was some pressure in the system. So we put in a can of R12, compressor works, AC blows ice cold. Sweet.

However on the ride home the temperature came up to the 100* line on the temp gauge and stayed there. AC on or off it was 100* and didn't cool down. I got home and popped the hood, neither of the electric fans were on. If the engine temp is 100*C and the outside temp is 85*F and the AC is on, shouldn't at least one of them be on?

I also got a little missing sitting in traffic which was new. You could watch the oil pressure click up and down a hair when it would miss.

I've got fuel and air filters for it, hopefully that will make it run better, the filters based on the logos on them are probably 10 years old.

The car showed no signs of having bent rods.

Meant to put this in diesel discussion, but it should be okay here

JohnM. · #2 08-12-2011, 04:35 PM

The diesels may be completely different in this regard, but the front aux fans don't turn on until 105C on the gassers. However, you are correct that with the AC on, the fans should be spinning at low speed. I'll let others chime in on the culprits of that issue.

But I wouldn't worry about 100C on a new car that you have no personal history with, and have no idea how old the cooling system is, overall tune, etc.

Tanksowner · #3 08-12-2011, 04:38 PM

My dad is having a similar issue with his 300SDL. Unfortunately, we also are unaware of the root cause.

compu_85 · #4 08-12-2011, 04:39 PM

The fans kick onto high speed at 105* as I recall. Low speed should be sooner from refrigerant pressure. How is the fan clutch? Mine was dead and that will really make the temp start to creep up!

-J

DieselPaul · #5 08-14-2011, 07:35 PM

How do you test the fan clutch?

I put 12V to the connector on the fan, and they came on at low speed. So maybe my relay is bad.

DieselPaul · #6 08-15-2011, 03:23 PM

Okay, googling I came up with a thread about an 87 420SEL. It said the low speed fan relay is the D position, which on my car is an ice cube relay. I have 3 spare ice cube relays, none of them made it kick on.

The temperature went enough above the 100* mark that I could see the white line below the needle. I turned the ac off and it cooled off a bit, but I popped the hood when it was that hot, and still had the AC on and the fans weren't even on at low speed.

So "stepdown" relay? Where is that located?

DieselPaul · #7 08-17-2011, 07:23 PM

Update:

With the key ON if I unplug the blow two pin sensor/switch in the coolant elbow on the top of the head both fans come on.

Is this indicative of a dead sensor/switch?

This guy, (borrowed the pic from googled)