72 280 sel overheating - PeachParts Mercedes-Benz Forum

andyj · #1 08-30-2003, 01:53 PM

Have had an overheating problem with my 280 4.5. The symptoms were, if the outside temp was above about 80 (most of the time in Texas) it would overheat after about 20 minutes at highway speeds. I cored the radiator, replaced the water pump and thermostat, adjusted the timing and while it improved somewhat it still overheated.

Today after talking to a mechanic he informed me the the 4.5 has a reverse flow and that the thermostat is operated by the flow through the heater. I am not sure if this is correct but to test I bypassed the heater core and this fixed my problem.

Evidently the flow was restricted and impacted the operation of the thermostat.

psfred · #2 09-01-2003, 04:46 PM

That's weird, the heater valves would be closed (I assume) in Texas in the summer, and there is no flow through the core.

I'd suspect a large air bubble in the engine, the 4.5 is rather difficult to bleed properly. The usual fix is to remove the supply side heater hose and let the air out, so bypassing the heater core probably flushed the air out.

Have you pulled the block drains and cleaned out the crud so you can do a decent flush on the block yet?

Peter

tosbt · #3 09-02-2003, 03:05 PM

New hand made muffler system here in Austin works very well, power is restored BUT runs just a little hot, about 195F at idle. When I drive it runs about 185F. Does not seem to be a lot of pressure on the hose. Have changed the Thermostat, flushed the radiator. Think maybe a Big air bubble? Suggestions? Got to drive it for the first time in three weeks. Was really smooth with great power. Nice car.

psfred · #4 09-03-2003, 01:04 AM

Tobst:

More likely less fan than you had before -- what condition is your visco clutch in?

195 at idle doesn't bother me, nor does 185 running, that's where mine sits all the time.

Less backpressure may be giving you more power, so more heat.

What did you use for mufflers?

Peter

tosbt · #5 09-03-2003, 10:04 AM

Peter, clutch and fan were check yesterday, judged to be in good shape. How would I have wound up with less fan? Actually at idel the temp gauge gets about 2/8 inch from red line but has to sit a good while before it gets there. I can drive it and like I said drops to 185, stop at light sit for 60 secvonds or so and its at 195, what really bothers me in not today, most of the heat has left central Texas but when we reach those 105 days again I may be in trouble. Has real good power now, the muffler shop used a MB rear muffler and some Japan for the front. It runs really good now but would love to see a constant top at 195F. May go to syn for the trannie.

psfred · #6 09-03-2003, 08:07 PM

Tobst:

Sounds like both fans are out of commission! Does your aux fan run? If not, see if you can get one from a W116, it's a bolt in and it's bigger

. Relay or fuses can get corroded and fail to turn it on.

I'd also bet the visco clutch is shot. You should hear it cut in -- that huge metal fan should make plenty of noise! If not, fill it with silicone fluid, available from Toyota (do a search to locate the thread, I've forgotten it). It should be running at 195F, most definitely at higher temps.

It is normal for the guage to go up to the line between 175 and the red zone, but at that point the aux fan should come on and the vac retard should drop off -- check the 212F fan switch for operation (single post connector on crossover on intake).

Peter