W-126 Overheating problem

[cam69ss]

I have a 1990 300SE with about 190,000 miles. I replaced both aux. cooling fans this past year, the engine fan clutch, thermostat, water pump about 40,000 miles ago and I replaced the radiator about 2 years or 55,000 miles ago with an aftermarket radiator made in Israel. The car is experiencing high running temps at 65mph+ with outside temps above 78F. It will go right below the 100C mark. In stop and go it will raise to about 110C and with the AC on it will go to about 115C before I turn the heat on to cool it down. I think the aftermarket radiator is the cause of my cooling problem. Is there anything I can do to check it? What are your thoughts?
Thanks,
Dan

[GregS]

Before you do anything, replace the thermostat. 40,000 miles on a thermostat is enough to wear it out. In fact, they often don't work correctly when brand new. The second simple thing I would do is check the consistency of the coolant (should be 50/50 max.), and also replace the radiator cap.

Good luck,

Greg

[sixto]

When you check or change the radiator cap, clean the neck of the reservoir. Sometimes the plunger element of the cap sticks to the neck and can't lift to relieve pressure.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[Toxicant]

I had a 126 that overheated also and it started this around 50K miles. I couldn't find a thing wrong with it and did some research and a guy that did rad repair said he had found on those cars the rad plugs up in circle right behind the cooling fan. He had no idea why but he thought it might have to do with it being cooler in that area. I don't know but I replaced the rad and had no troubles again.

But of course you should change the thermostat, cap and 50/50 mix first.

[afmcorp]

hi cam

in your post you never mentioned water loss nor did you mention what type coolant you used. and from your description of turning the heater on to cool down i am assuming your cooling system is performing ok.



1. on aluminum using the Pgreen brand is not the best. you need something specifically made for aluminum. if however u did use the Pgreen brand you might be able to get a radiator shop to use a solvent to try and clean out any corrosion. of course that has other negative issues. talk it over with that vendor and see if they can "Guaranty" against problems. maybe MBZ dealer can help with factory approved stuff.

2. on the new rad did it have the same number of cross flow tubes as the mbz brand. is the shroud still intact. are the fins of the rad clogged up or bent over restricting air flow.

3. i'd go ahead and replace the thermostat 25$ is cheap insurance. but before i threw the old one out i'd heat a pan of water and drop it in. if it doesn't move much or at all toss it. if it moves fully open / fully closed it's a keeper save it for next time.

good luck.

[1991300SEL]

The brand of coolant used has nothing to do with operating temps. The proportion of coolant to water does.

I live in a warm climate and have experienced reduced temps by using a reduced concentration of coolant to water. Coolant(any brand) does not dissipate heat well at all.

[R@Z()R]

I was having a similar problem in my W126 1986 560 SEL. Check the hose that goes from the coolant reservoir to the overflow reservoir (which is located in the wheel well.). It's the small hose that looks as if it goes into the wheel well. You need to remove the passenger fron wheel and there are about 10 bolts you need to remove from the inside of wheel well. Once you do this, you should see the hose going to the overflow reservoir and check to see if its connected/cracked. I found that in my car the hose was just "stuck" thru the hole into wheel well and not long enough to connect, so I got a new hose and it worked.

I was having trouble with this in my car and it ended up getting worse, by running hot and then I had to replace my coolant reservoir (due to a crack in the seam that was not visible to they eye upon removal and examination).

R@Z

[afmcorp]

just to clear up a few things

1991300SEL

i beg to differ and i'll agree with you as well. if you'll read cam's post again he never mentioned boil over or losing coolant etc:

what he said was... the needle tipped the scale quite hi up at the 100 mark. so i will agree with you that the proper mixture will cause a flux in the ability to cool. however the type of coolant does matter. if you use the pgreen stuff without the corrosion proof chemicals for an aluminum system you will have a problem. and this is what i was referring to. (pls take the time to do a search on cooling system corrosion to see what i am referring to).

back in the old days 60's & 70's you could buy bottle of cooling system flush but i don't know about now if it's ok to use. even the dealers had this stuff. i think prestone sold it also.

cam69ss

sorry for my detour.

you didn't mention if this just started or was a problem from two years ago when you replaced the radiator.

if you have had a pressure test and found the system ok then it is sure to be a blockage somewhere. i'd still pull the thermo and replace it ... or at least test it in a pan of water. you said you can turn on your heater and get the hot air. so those lines seem ok. i'd head for the thermo.

if the thermo is ok, then you're justified pulling the radiator and getting it tested for flow. you know you might trying getting a coolant system flush unit from the pgreen people they can't be much over 10$ then you could back flush the coolant, maybe even clean out the radiator and refill with a couple of gal of your best coolant.

good luck with your problem
tks
craig

[1991300SEL]

afmcorp:

I suspect that the MB coolant offers better corrosion protection. It's all I've ever used.

My point deals with the belief that MB coolant is "cooler" than anyone else's. I've read countless posts here that suggest this to be true.

People who believe this are likely sending "what I want for Christmas" letters to St. Nick every December.

No ones coolant "cools" any better. It's the proportion of water to coolant that affects heat transfer.