This is an update to the below original post I made earlier today:

I just drove the car, and the coolant light came on when I got back. Tank is muddy/redish/brownsih looking, I have to open to check level. Can I add normal Preston pre-mix stuff to hold me over until Monday/Tuesday. Does color of tank mean rust/air in system? The car has been to dealer 3-4 times since May for cooling related issues. They replaced coolant when they did Head Gasket in May, and had to have at least added coolant two weeks ago when they did the Thermostat. Even if the problem I mention below is in fact within normal temp ranges, you'd think they'd at least mention the fact that the tank is showing signs of bad things, if that be the case. I'll have to speak to them on Monday. I've spent @$$loads of money on what seems to have no results, save for the head gasket, that was of course leaking.

Original Post:
I have a '93 300E, 3.2 I6, late '92 build, only 70k miles on it.

Temp
For the last few years, the car runs hot in slow or stop and go traffic, especially on hot days. The temp needle stays around 80-85 on the highway, but then reaches up to 110-ish when in slower traffic, especially after coming off the highway into slower local traffic, red lights, etc. The aux fans and engine fan all work. I tried to turn the engine fan with engine off, and it turns as much as I want to turn it, all the way around. Old posts here say that would mean it is going bad, not spinning at full speed, but M-B mechanics and other service people say that it is normal, that it should turn when off (that being the purpose of having a "clutch", not fixed to engine). Did the turn-fan-by-hand test only apply to earlier models? Or are the dealer techs wrong? Dealer did the head gasket early this summer, and problem seems to have become worse since then, but that may just be the summer heat. Had the thermostat replaced a couple of weeks ago, little to no improvement in temp. No leaks found.

Idle
The car sometimes has a slightly "bobbing" fluctuating idle speed when sitting still in park or in D.

Tranny
Clunks into gear from park or R. Sometimes when I make a special effort to pause and wait a second or two when shifting from reverse to drive, I get a short slip and a clunk before car jumps forward. After that, when driving, car holds gear long before upshifting when cold. Hard, heavy acceleration pulls up to redline, shifts smooth and crisp.

Thanks for any help or advice anyone can provide!!!

Just went out and checked the coolant level in tank after letting car cool for over an hour. It is up to the level of the horizontal seam in the tank. Seems normal. But then why would my coolant light be on? Also, although the tank looks muddy, a look inside with flashlight shows clearish looking fluid..not very redish or greenish. Can see right through it to the bottom of the tank. Any ideas?

Replace the cap, it's allowing coolant to boil out into the overflow tank under the fender. When it cools off, it pulls the coolant back in.

This will cause it to run hot, too.

New cap is cheap.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks. I actually inspected the cap based on old posts here, it looked fine to my eyes...hehe. If the cap is allowing it to boil over into the overflow tank, would I notice any "mess" or wetness anywhere? Is there any way to be certain that it is the cap? Visual signs, etc?

Also, the light has never come on before, although the "running hot" issue has been happening for months and even a couple years really....

Eventually it will blow out of the overflow tank and onto the ground near the passenger side front wheel. Unmistakeable. Usually only overflows to the ground after a hard highway run.

I would suggest a citric acid flush if you have rust in the coolant when it boils over.

My TE did this in the summer with the AC on - pulled into a rest stop, and bingo, on comes the coolant level light and there is coolant all over. Happened to my sister shortly before (a long story about a blown head gasket so she was using Mom's car).

Cured it by finding an auto parts store that had an MB cap.

A new visco clutch cured the "running slightly warm" in traffic thing, too.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

First of all replace the expansion tank cap. You cannot tell if it is holding pressure just by sight.

When I first bought my car, (94 E320 Wagon), the coolant was rusty as you describe. It was also running very warm but not overheating. But the brownish coolant is why I got it for $3000 less than the man was asking. That was the amount of money I reckoned that I needed to spend to fix the car and make it right.

I spoke to the MB service advisor and he suggested buying a bottle of Shout laundry pre-soak. I added the Shout, drove the car about ten minutes, and drained and refilled the system about 3 times, (running the car 10 minutes each time). I removed the thermostat in order to properly flush the car. Then I replaced the anti-freeze. (I used MB antifreeze) That procedure cleaned up the coolant. There is still a little residue because I didn't replace the expansion tank. I plan to change the coolant once more before the winter and that should get rid of most of the lingering schmutz.

I later did a bunch of work, including replacing the head gasket, (because it was leaking oil on the right side of the engine). I also replaced the water pump, because the veins get rusty. I also replaced the viscous fan clutch and the thermostat. I replaced the hoses because they were compromised by the contaminated coolant.

The car is running much better now. I didn't change the radiator, but I would have if the car were still running hot. They are not that expensive, under $200, and are fairly easy to change. Last winter I changed the radiator on my 97 SAAB 9000, and the car has been running cooler and totally stable ever since.

One problem I haven't resolved is that my coolant light does not light when I turn the key on. I assume that the bulb is dead.

Best of luck, let us know what you end up doing. I have to say, it is curious that your coolant is contaminated now even though you head gasket was changed so recently.

Just drove the car again and did some checking under the hood. I tried to rev the engine at idle to see if the main fan would disengage at high RPM, but when the rev needle hit 4k, the engine started cutting out, as if it hit a protection rev limiter or something. Is this normal? It pulls to redline when driving.

Not sure if the coolant is actually muddy anymore. I have a feeling that the tank itself is stained from before the head gasket was done. When I shined a flashlight into the tank, it seemed clear, almost watery. I could see to the bottom of the tank. From outside though, the tank looks dirty on the inside above the coolant level, and looks as though there is condensation on the upper side walls of it.

Thanks for the advice guys. I'm going to mention all these points you mentioned above to the dealer on Monday or Tuesday, and make sure everything is rectified. I'm going to pull out all the cooling related service invoices that say "customer states.....could not duplicate...performed checked...normal...we don't care....x amount labor hour for diag" hehehe.

Today, I checked the connector for the level sensor as advised by tkamiya. Dry as can be...and no coolant light was on today. Weird...perhaps it's one of those things that's ont he verge of breaking. I still suspect the connector/sensor that tkamiya advised about. I guess we'll see during this week. I plan to do some 40 mile highway runs, I usually get enthusiastic along the way and the temp needle is around 100 within 2 traffic lights after I come off the highway. I'll see if there's any wetness on the connector then, and if any coolant comes out of anywhere...

Yes, this is normal when not in gear.

Shout laundry pre-soak - might be ok for de-oiling an engine that's experienced a blown head gasket.

Fred's idea about the citric flush would be more in line with what you need.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"