Hot but not overheating - Page 2 - PeachParts Mercedes-Benz Forum

scottmcphee · #16 06-22-2018, 06:32 PM

Quote:

Originally Posted by mhin1956

Still no solution. Driving in this am at 80 degrees (f), car started out on interstate at apx 85 on temp guage (c). slowly climbed at interstate speeds about 10 degrees. AC not on. Came off interstate into town and stop and go brought it up to 105. driving slowly for apx 6 blocks brought it down to 100. Have checked for air in system, none found. Temp sender to be replaced this weekend, but think car is running hot. Found thread that said maybe exhaust restriction (??)..anyone know how to test or what to check? MPG seems ok, car is driven daily.

Have you squeezed the upper hose and found it to be rock hard?

I know, not a happy day to find that out... but you have to try it.

Also, look for oily film in your coolant reservoir.

vstech · #17 06-23-2018, 07:39 AM

Fan clutch.

mhin1956 · #18 07-24-2018, 09:14 AM

Update
first issue: after two fan clutches, etc and lots of testing, have found that possibly belt is worn/slipping, have a new on on the way. Cleaned old one w/ dish soap and rinsed (on car) and seems to help - keep fingers crossed.
second issue, no AC. Jumped klima and car is super cold inside, and NO affect on engine temp, elect fan working well. So after researching, think possibly belt slipping. I did a search on compressor rpm sensor test. Mine has resistance of 895 and no voltage at all, with engine running. Would this be the culprit for no AC? Read that jumping does bypass cutting off compressor at all (?)
could someone confirm RPM sensor test method?

THANKS
Mark
btw 420k now and climbing, runs great!

Diseasel300 · #19 07-24-2018, 11:22 AM

It's highly unlikely that a "slipping belt" is causing your overheating issue. If it were, you'd be having problems with charging and power steering. The serpentine belt runs EVERYTHING, not just the water pump/fan. Are the fan clutches you're running brand new, or are they used?

As a reference point, it was 112˚F here yesterday and with the A/C cranked to Max, my temp never got over 90˚C in slow traffic. Prior to upgrading to the OM606 turbo clutch/fan, days like today would have easily had it running 105-110˚C.

The Klima is only part of the equation when running the A/C. You have a high/low pressure switch on the filter/dryer and you must have a ground present at the "enable" pin on the Klima relay for it to do anything at all. The CCU can have an internal failure that prevents it ever engaging the compressor. Went through it on my own SDL due to crappy soldering (pretty well every electronic issue) and a failed transistor chip on the PBU board.

Jumping the pins at the Klima relay only rules out the contacts on the Klima relay, it doesn't rule out anything that controls it. You need to have a working Tach, the pressure switches need to work, the cutout on the throttle mechanism needs to work, the overboost switch mustn't be tripped, the speed sensor (nothing more than a magnetic pickup) needs to provide a signal, etc.

vstech · #20 07-24-2018, 02:00 PM

One thing that WILL cause cooling issues is belt routing...

It can be routed where only the wp slips...

mhin1956 · #21 07-24-2018, 05:23 PM

thanks for the responses. The belt routing has been done several times to that is not it-have replaced at least 3 in last 20 plus years. CCU and other sensors have been replaced, tested and all appear to be ok. CCU was swapped out w/ known good one and no change. Only think I was looking for was a test or confirmation of what to look for to see if the ac rpm sensor could be culprit.

Texasgeezer · #22 07-26-2018, 11:34 AM

I'm glad this thread started, I've learned a few things from other's past experiences.

My most frustrating heating issue turned out to be due to aluminum corrosion causing small particles to lodge in the radiator tubes & slowly blocking the coolant flow. This was in the late 80's when I was younger & dumber & didn't know about aluminum corrosion & how to reduce or prevent it from happening. After changing my 23 year old water pump about six months ago & finding zero corrosion of the engine mounted aluminum coolant passages, I'm committed to only using Mercedes rec' antifreeze and changing it fairly often to keep the corrosion additives refreshed.

97 SL320 · #23 07-26-2018, 12:24 PM

Do a cylinder leak down test with the rad cap off. This checks for a combustion chamber to coolant leak. ( head gasket / head crack / cylinder wall crack )

There are combustion gas leak test kits that use a chemical however they won't conclusively find a small leak.

Mxfrank · #24 07-26-2018, 12:34 PM

Quote:

Originally Posted by mhin1956

Update
first issue: after Would this be the culprit for no AC? Read that jumping does bypass cutting off compressor at all (?)
could someone confirm RPM sensor method?

The Klima reads two speed signals and compares. One is from the compressor, the other comes from the EDS control unit and is synthesized from the crank position sensor. The likely culprit is the electrolytic caps in the EDS unit. Diesel300 has posted some info on replacing them. You need a scope to verify the two speed sensors, but my bet is that they’re ok.