A diesel in stop and go traffic actually needs less air flow over the rad, at idle even less so. I’ve seen my temp go from about 85 C to 75 C after getting off the highway and driving in slow stop and go traffic. I know it’s counter-intuitive but true.
I also think it’s the rad. Perhaps it just needs a good flush and fresh coolant. But the rad is obviously not able to pass enough extra heat from the coolant to the air even at highway speeds.
My 1985 300D turbo does the exact same thing. I drove it From Nashville to Florida and couldn't run the a/c very much. I replaced the thermostat, fan clutch, and the condenser fan works. I'm thinking the head pressure on the A/C unit is too high causing the compressor to have to work too hard. Maybe the orffice tube is clogged. I don't know, but I can't figure it out either.
My 1985 300D turbo does the exact same thing. I drove it From Nashville to Florida and couldn't run the a/c very much. I replaced the thermostat, fan clutch, and the condenser fan works. I'm thinking the head pressure on the A/C unit is too high causing the compressor to have to work too hard. Maybe the orffice tube is clogged. I don't know, but I can't figure it out either.
Does yours only demonstrate this at highway speeds? Mine does it only when on the highway going over 45-50mph. I can sit in traffic all day long with the A/C running and it never goes above 90. This is why I was leaning so havily toward the fan clutch being the culprit. It never goes over 100 though, but it will stay steadily at the 100 mark or just a tiny tiny bit below it until I pull off the highway...then it drops back down to 90 within a minute or two. Could this possibly be a sign the compressor is going bad which is causing excessive strain on the motor? I should also note that the A/C has been converted to R134a.
Last edited by no-blue-screen : 07-13-2006 at 08:41 AM.
The fan doesn't really do much when you are driving at highway speeds.
okay, I will buy that but here is what is puzzling me:
If it were the radiator, thermostat, waterpump, or a combination - would I not see teh cooling issue constantly rather than only at highway speeds? Cruising on the highway should be much less of a strain on the cooling system than stop-and-go traffic since there is much more air flowing through there. What I am seeing doesn't make any darn sense to me. I run at 90C unless I am highway cruising at 50+mph. What I was thinking is that the fan clutch is bad and when the rpms go up above 2500, the fan totally locks up and doesn't move any air at all.
And again....all of this only happens when I have the A/C on.
-OR-
Is this normal for these cars with the A/C on? Like I said, it never goes above 100C but it will stay at that temp until I pull off the highway, or if I shut the A/C off it will cool back down to 90.
Most of the time the answer is already give somewhere and
since this forum has a search function it is easily found also.
Louis.
Hi Louis,
That thread has some good information on the fan clutch, but it doesn't address my issue. It is the exact opposite of my issue. I have used the search function and wasn't able to return anything that addresses the issue I am having, hence my new thread.
may be the aux fan is over heating and shuting off this would cause the problem your describing how can you be sure it runing at highway speed . it should always always be on when you switch your ac on if ac is off it will only switch on over 100 c give or take 5 or 10 degrees depending on how relible the swictch is
I know the aux fan is working because I can hear it when I am not on the highway. Again, I think if the aux fan were overheating, this would be more likely to happen when cruising around town since less air is moving through it at that time. This weekend I am going to replace the fan clutch and install my newer 9-blade MB fan to replace the original 6-blade design. At this time, I also plan to replace the coolant and thermostat since I already have those parts as well. I also have a new Laso water pump laying around, but I am not sure I want to put that in until I am ready to replace the belts. I know the 9-blade fan won't move any additional air, but it should be quieter and require a tiny bit less energy to operate than the 6-blade design.
In the W126 forum there is a description of similar symptoms and 1 possible repair. The author drills holes in the Thermostat plate, first 1, tests it and then 2 or 3 holes if necessary. Slower to heat up, but apparantly compensates for the 126's cooling system which is not (according to the author)entirely up to snuff. Might be worth a try if all else fails.
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