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Old 08-19-2003, 11:50 AM
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Join Date: Nov 1999
Location: Matthews, NC, USA
Posts: 133
500E Running Hot

After 2 weeks and numerous improvements, I am still having some residual heat issues.

They started with a leaking heater hose. Easy to spot and fix. Still runs hot, boils fluid in overflow tank. Radiator had partial blockage in center section and fan clutch not properly working. Easy enough, replaced radiator & fan/clutch. Radiator cap old and deteriorated. Easy to fix, replaced Cap. Thermostat stuck next. Easy enough, replaced thermostat. Conditions obviously getting better, step by step, but still not 100%. Maybe sending unit/gage is wrong? Easy, checked with temp gun...dash gage is very accurate.

At idle car is fine, warm, but fine 95 to 100 C.
The minute you start to drive off, temp begins to rise gradually up to at times as much as 110C and once when ambient temp was some 90F+, actaully approached 115C. I immediately turned the heater on and temp dropped to below 100C. Activating A/C obviously aggravates the heat condition, activating heater seems to solve the problem. Driving obviously generates more heat, stopping in traffic makes it worse, unless I turn the heater on, bring the temp down, and then it seems O'K until I drive away again.

Yes at times the heat will rise enough to trip out the a/c compressor. As soon as the temps drop a little (i.e. less than 1-2 minutes), the a/c compressor kicks back in. At these times it may cycle many

I do have a belt tensioner which appears less than new. There are occasional chirps which lead me to believe that there may be some slippage but rarely (unless full throttle accel) is the chirp/slippage enough to cause the a/c compressor to trip out. I plan to change it anyway, but could this be the root of evil?

I will check the coolant for Hydrocarbons tonight (i.e. testing to rule out leaking/marginal headgasket?)

I also notice that 2 of the 3 flaps on the radiator shroud are missing. My understanding is that at idle or low speed, the fan draws a slight vacuum and keeps the flaps closed enhancing induced draft air flow across the radiator. At speed, the forced draft air flow (motion induced) overides the fan and pushes the flaps open increasing air flow to more of the radiator's surface. While this may or may not be significant, I will duct take them closed this afternoon and note whether there is any change.

Can you think of anything else that I should check?

While it may not be the solution to the root cause, I am considering a coolant enhancer. Have you ever heard of "Evans Cooling" its at THey have a product that is supposed to reduce/eliminate vapor formation in the system and thereby reduce hot spots, pump cavatation, etc. all of which contribute to engine heat. They admit that under normal operation (i.e. below say 210F) there may be little to no improvement. This appears to be somewhat like the "water wetter?" that I remember everyone referring to in the site.

Any input would be appreciated.
Last thought, I have one or two heater hoses still original on my 92 model. Is it possible that they are weaping slowly (too slowly to notice a coolant loss, but enough to introduce air into the system) and thereby creating an environment conducive to vapor formation, which inturn can increase the potential for some small level of pump cavatation and partial overheating??

I feel that I have allowed my thought process to get far to theorectical, but I have passed all the simple stuff that I can think of?

I will update tonight or tomarrow after the above two tests (1) & (2) are complete.



Last edited by dwight hinton; 08-19-2003 at 11:57 AM.
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Old 08-19-2003, 09:12 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
I doubt you have a blown head gasket. It is possible, but not likely.

There are a number of upgrades you can try.

Check in the Hot Rods section and search. I have read quite a few posts on this on.
Donnie Drummonds
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Old 08-19-2003, 09:35 PM
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Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
The M119 engine tends to run hot in a W124 chassis like yours and mine. Mine will easily go to 105-110 in summer heat, in stop and go traffic, with AC on. Having said that, yours is too hot.

My thoughts:
1. If you suspect a leak, the only way to really find it is to pressurize the system. You need to buy or rent a pressure tester. I bought one. They cost about $80 but I think it's worth it.

2. Do you have a new "radiator" cap? If not, get one.

3. How old is your water pump? Is it OE? Some aftermarket rebuilts are said to have smaller vanes so don't move as much water.

4. How are your aux fans running? Have you tested both low and high speed operation? In my case, getting them running again (by replacing a burned out resistor) got the temp down.

5. The other main mod is to "fix" the fan clutch so the mechanical fan is working 100% of the time instead of temperature-dependent mode. It is set at the factory to only couple when it sees about 107-109 degrees of AMBIENT AIR TEMP which means by the time it couples, the coolant temp is MUCH higher. Stu Ritter of the STAR magazine has a good fix. My tech modified his approach. I'll be happy to detail it for you if you are interested. This single mod has made more difference for me than any other single change I've made. Now, even in 100 F temps, coolant never exceeds 100 C in traffic.

6. Water Wetter helps a little but not much. You still have something wrong somewhere if you are seeing 115 C. On the other hand, do make sure you have NO MORE than 50% MB coolant. Seems to me that every time my coolant gets flushed, I have more like 60/40 coolant/water. If I take out some of the mix and add straight water to get more like 50/50, or even 45/55, the temp does come down a few degrees. You can check your mixture with a Prestone coolant tester.
'93 400E
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Old 08-20-2003, 02:55 PM
Registered User
Join Date: Nov 1999
Location: Matthews, NC, USA
Posts: 133
Water Pump is only 2 yrs old,
pressure test reveals no leaks.
Coolant Chemical test reveals head gasket is not a problem.
Aux fans, both on, max speed.
Tried installing Guido's early fan activation device, fans come on sooner, but problem is after they come on, still hot. While I like Guido's mod, my problem is bigger than that.
Seems to be worse while driving, not at idle.

At Idle...100C (with ambient temp of 85F+) with A/C on

AT speed...110 to 115 with A/C on.

This car has always run cool! Rarely ever ran over 100C.
I mean max 105C at warp speed, A/C on, driving like a mad man in summer heat with ambient temp of 100F.

While I am interested in mods to fix the problem, I can't help believe that something is wrong. This car never needed a mod before.

Why is it suddenly a problem?

Last edited by dwight hinton; 08-20-2003 at 03:01 PM.
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Old 08-20-2003, 03:11 PM
mike690003's Avatar
Registered User
Join Date: Apr 2003
Location: Miami,FL
Posts: 807
A new expansion tank and radiator cap is worth a shot. My car overheated all the time, and no one was able to pinpoint that my bottle and cap were just too old. They would not hold pressure, even though the rest of the cooling system was a-ok.
1987 mercedes 300E
1995 e320 conversion(hated the 300e grill)
HID/Xenon (D2S)
Keyless Entry
Monochromatic Paint (Custom Blue)
Smoked Tails
Flat Badged (front)
Debadged (rear)
custom "carbon fiber" console
18 inch HP EVO rims
Sold! Now I drive a Monte Carlo SS

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Old 08-21-2003, 05:46 PM
MrCjames's Avatar
California Dreaming
Join Date: Jun 2003
Location: SF Bay Area
Posts: 599
124 with a 119 engine

This is something I had a great deal of experience with lately. If you study the placement of the R/S auxiliary fan motor you will notice that it blocks air flow to the Fan Clutch hub. Since the bimetal strip gets little heated air it does not have the opportunity to heat up thus never really allowing the fan to fully engage.

Solution: On the blue 2-pole switch add a 2K 15 turn potentiometer. Dial the resistance in at 1405 ohms and solder it in parallel to the female contacts.

Let me know how this works for you, I have personally resolved 4 vehicles to date. One of the added benefits to making this modification is the oil pressure will no longer drop below one bar while driving around on very hot days.

Good luck
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