so if i have a bad pump, what exactly goes bad in these? there are no leaks anywhere

thanks,

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1993 300E, 2.8 M104 .....

If your system has no leaks then pressure should remain in the system for an hour or two after turning the engine off. Releasing the radiator cap after an hour should get a pressure response.

If you have a small leak or air bubble problem the car should not be getting up to 105 degrees when traveling at highway speeds. You have a circulation problem. - Faulty water pump, thermostat, radiator or some blockage somewhere. You can get a pressure test done by a radiator specialist.

Before you do any real damage I would disassemble the system and reverse flush the engine, radiator and inspect the pump etc. This is a time consuming job you can do yourself but better than replacing a head gasket.

Of course you could have a faulty head gasket anyway.

Does turning the heater on when traveling make a difference?

Someone previously mentioned coolant bottle failure. Here is an image of a failed one. The split was in the rear of the unit where you couldn't see it. Strong heat proof glue wouldn't fix the problem.

There are no leaks as there is no coolant level change....

What is the relationship with the heat?

Thanks,

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1993 300E, 2.8 M104 .....

A leak will cause the system not to pressure to the correct level. The whole system relies on pressure to keep the heat down.

My cooling system had several leaks in the old hoses when I bought the 2.6 and it NEVER over heated. The previous owned was topping it off every couple of days. I could squeeze the lower radiator hose completely flat when the engine was hot. The temperature never climbed over 95c in the 2 weeks before I replaced every hose. No more leaks now and the temperature is exactly the same.

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CENSORED due to not family friendly words

If the radiator gets hot you have water flow.
If the water coming out of the radiator is still hot, the radiator is bad or you have restricted airflow.

Rob

So Update: I have a serious problem

burped it last night, and decided to go to the beach today (2 hour drive each direction)...I thought highway driving would keep it cool. Ambient temp outside was 85 as the temp LCD was showing while cruising on the highway.....

At roughly half an hour into the drive, the temp started to creep-up towards the 100 mark....I had to turn the AC off (that was not fun)...the temp remained around 100-105 all through the drive. I felt bad for my Aux fans coming on at 80MPH, they must have had a horrible time...105 is the maximum it got, but it was toasty nearly 100 all the way....

at mid-day, and as i arrived at my destination, ambient temp was 95-98, and the car was constantly going from 100-105 in stop and go traffic with AC OFF........

On the way back this evening, it was raining, and ambient temp was 72. car operation temp was normal all through the drive back, but with AC OFF. although it was a tad higher than the 87 mark......

So two options left:

1-Poorly performing pump, which is possible, but seems highly unlikely as there are no leaks...unless the impeller is wobbling in there or broken...

2-My radiator, although new, is an aftermarket generic an rather cheap brand. My theory is that it is poorly designed or put-together, and is incapable of reaching the cooling efficiency needed for these engines .........that will explain why temp was normal in rain as the ambient air and rain could absorb more heat than in the heat of the day...

So guys, which is it? I will be fixing this within a day or two so i need a verdict. I put too much money into this engine and cooling system to loose it all in a blink of an eye....

Thanks for the input thus far,, keep it coming......

I am pissed

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1993 300E, 2.8 M104 .....

Did you have the hoses replaced along with the radiator?

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CENSORED due to not family friendly words

Yes, all hoses are new...system flushed more than once....coolant is zerex-g5 with 50% distilled water...

pump is Graf. new...
coolant tank is new
radiator cap is new
thermostat is new Waehler? brand, last week i had a new behr one and same problem....
No leaks anywhere...

no oil in coolant, no coolant in oil.....

I am confused about this...what do you think?

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1993 300E, 2.8 M104 .....

and just to throw some additional ideas into the mix....could this be an engine/ transmission issue since the problem appears after a rather long period of time as the drivetrain warms up? could my transmission oil be too hot?

thanks

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1993 300E, 2.8 M104 .....

Anything other than a genuine Behr radiator should be considered suspect in my book. There are too many unknowns with off-brand radiators....or so I was told. I bought a Behr for the same or less than the off brand but had to shop around quite a bit. The water pump (if its the kind with the plastic impellers) could also be the issue. No easy way to diagnose either. I think the inefficiency of a non OEM made radiator is not easily tested. The higher temps are caused by inferior construction or low quality materials or both. Can't really inspect the water pump without removing it. Just my 2c....good luck

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

I don't have experience with the 300E but check your trans fluid dip stick.
pink or brown? grainy?

How's the engine oil? 20/50, 10/30, 30 weight??

spark plugs fouled? dunno.

temp gauge OK ? I've read about those point and measure heat detectors.
you could 'calibrate' the temp gauge that way.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Temp gauge is accurate. I know that because it displays 87ish during normal operation (before overheating). it also displays 105 exactly when the Aux cooling fans kick in......

Transmission oil was changed recently. My transmission in on its way out i guess, as i have weak reverse, but i have never heard of it causing such an obvious overheat. other than the reverse, it shifts perfectly.....

MBDOC mentioned here that the Graf pumps are the only aftermarket pumps that use the an impeller and seal identical to the Mercedes pump. he recommends the graf when an original pump is not available or when you cannot afford the MB pump...

The radiator looks decent. the fit was not perfect as it was a bit wider then the behr it replaced, but it worked. maybe capacity is not correct?

I think i will burp the system and on ramps one more time and see..although i think i have a bigger issue....

Cruising rpm was around 2800-3000 at 75-80 MPH.....


Should i run the car without the thermostat for a day and see?

Engine oil is Delo diesel grade as recommended here

I have not looked at the plugs since i installed them 2000 miles ago....

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1993 300E, 2.8 M104 .....

At 80mls/h the aux fans are useless, they can never produce that kind of wind speed.
Even the normal fan does very little at that speed.
Have you checked if the fan is mounted the right way?

Have you checked the condenser? bent plates can reduce air flow. When it is dark, put a bright lamp behind the radiator (with the engine off) an look through the condenser.

If your new radiator has smaller of less water ducts and/or plates the capacity can by much less than the original one.

Rob

so anyone have any advice on how to approach this? I really don't know where to start....

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1993 300E, 2.8 M104 .....