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Old 07-27-2002, 07:26 AM
bdrought's Avatar
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Join Date: Apr 1999
Location: Milton Keynes, UK
Posts: 403
500E cooling thoughts/questions

My 500E runs between 90 and 110deg, with ambient of 20-25degC (and ac on). Now, I know this isnt too bad, but sometimes when its a bit above 25degC and I have the A/C on full, engine temps can climb to a bit above 110.

Firstly... went to check the thermostat, only to find there wasnt one in there. ( I presume the thermostat housing is the thermostat housing shaped object above the water pump that the top rad hose connects to).

Now... without a stat in there, water will flow both ways, surely? I.e. about half will go through the rad, and about half back through the block. I'm guessing when the stat opens it blocks the recirulation path to force about 90% of water through the rad. So with a stat in, it should run cooler?

Secondly, on the engine side of the rad, to the side of the mechanical fan there seems to be big rubber flaps blocking the rad. What the hell are these? I presume they lift out the way at speed, but is it better just to remove them? Are they to prevent backflow when at idle (with no ram air, just fan).

Thirdly.... Anyone noticed the Horn is in the way of the rad? Thats a fairly big area that has no airflow. Would there be much benefit in removing the horn and cutting that black plastic section away ?


Brian Drought
1999 Lotus Elise
1991 Mercedes 500E
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Old 07-27-2002, 01:34 PM
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Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
The 400E uses the same engine (M119), so I have some experience with this. First, I'm not really sure why the rubber flaps are there but mine has 'em too.

The thermostat is actually on the SIDE of the housing. I too was fooled by thinking it should come off the top.

RE: temps > 100C, as you know the owner's manual says it's OK, but like you I got tired of seeing those kind of temps, and also the engine computer will retard the timing when coolant temps get that high, so performance goes down.

Do your electric aux fans work? There are MANY, MANY posts on this subject so if not sure, do a search on this.

If they ARE working OK, like mine were, but you are still seeing higher coolant temps than you'd like, a good thing to do is to modify the viscous fan on the engine. There is a bimetal strip on the front of that fan which is set to couple the fan starting at ambient temps > about 107C, so it is really set way too high. It is fairly easy to "fool" it so the fan is on all the time. Stu Ritter (from the STAR) recommends using a small screw and 2 nuts to push the strip out a bit; my tech did it a bit simpler by grinding down the brass ferrule from the top of a spark plug so that the bimetal strip sits higher than the pin. It works really well, and mine never goes above 100C, despite ambient temps of 95-100F.

You'll have to pull the radiator to take off the fan for this mod, however.
'93 400E
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Old 07-27-2002, 04:16 PM
Michael's Avatar
Join Date: Jul 1999
Location: CT, USA
Posts: 2,699
#1: Make sure fans work
#2: Make sure coolant is of proper ratio; I run 45% coolant, and the car runs about 10 degrees C cooler than if you're running 55% or so.
#3: Replace your T-stat. If you're there, pop in a new one (and make sure small check valve is at the top)
#4: Pull top 1/2 of fan shroud (3 small 8mm bolts & 2 clips), then pull the clips that hold your radiator to your radiator upper support. Pry the radiator away from the A/C evaporator, and flush all the crap out that's invariably in thereKeep us posted-sounds like you're too hot methinks
"If everything seems under control, you're simply not going fast enough" --Mario Andretti

1995 E500 street car
1986 Porsche 944 Turbo S track car
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