92 300D Runs hotter in traffc, slower speed
 

Hi All,

We just acquired another 300D W124 2.5 turbo from a family friend.
Car runs out very well, has good power.
Only complaint or question is that it runs hotter in traffic and at lower speeds. Like it gets to the 100 degree line, the line between 80 and 120 on the gauge I assume thats 100. Our other car doesn't do that and this has me a bit worried.
On the freeway it stays at a constant 80 or a touch higher with no fluctuations at all.
The top hose also collapses after running for a long time, almost like the system goes into a vacuum state.

Any ideas on what this could be? Ideas suggestions as always appreciated.

Totally normal....especially with AC on. The temp gauge on your car indicates actual temp (as opposed to being an idiot gauge used on many cars that doesn't register the fluctuations).

My e320 did that with the AC on in stop and go traffic in the summer. After I hit a deer, which I believe knocked the carbon out of the aux fans, it never gets above 100. May want to sit in your driveway with ac on fully warm and see if your aux fans kick on.

As long as it stays out of the red, you're good.

Doesn't the car have an electric fan? It stays off until the temperature reaches 100 degrees C and than it starts blowing until cooled enough. That will cause a fluctuating gauge, but it is normal.

I believe on these cars it's somewhat higher that it comes on in response to coolant temp....like 105 or 107. There are two aux fans. The come on at high speed in response to temp; or at low speed, when AC is on, in response to refrigerant pressure.

Add a manual switch for the aux fans. Turn it on when you're sitting in traffic and you'll never see 100c. it should also make your AC efficient in that situation.

I agree with all the above but I think the radiator cap is also bad. That can cause the upper hose to collapse. There should be pressure in the system if it is hot. As it cools, it should pull coolant back in until the pressure in the system is 0 psi and the hose should never collapse.

Paul

On my 300D. I've got a new radiator. In non-a/c scenarios the temperature is always around 80C. It never floats up to 100C or near it.

When the a/c is on and you are in stop/go traffic it can get to 100C.

My 1992 300D does the same thing (gets to the higher 90c temp range with AC on a long highway hill when it's hot out. Without AC it's just above 80c). Note that I have a new radiator, thermostat, headgasket, and water pump within the past 12 months or so. So my system is nearly as good as new. Mechanic also says it's normal.

But, I also installed one of these "cool harnesses". Works like a charm.

Link: K6JRF Auto Page

I have the 95 degree version and I believe it helps govern the temps well enough that I don't worry any more. Before that I don't recall the fans ever coming on even if my temp hit or bumped just above 100. I guess I rarely (if ever) hit 105 or 107 etc back then. But it comes on exactly on the 95c level on my gauge.

I missed that part about the collapsing radiator hose earlier. Does the top hose collapse with the engine still running, or after it's turned off and cooling? How old is the hose? Does it feel like it's gone soft? Replacement hose if not in like new condition (check the rest of them too) and a test of the radiator cap would be good ideas.