My 99 seems like it's 'running hot'. On the highway, it's fine, around town, seems fine. But, after a run, and a heat soak, the temp guage runs up about 1/2 way between 90 and the next mark, and just seems to stay stuck there. The fan clutch is engaged at that point, and it never seems to cool down, if I take short hops. The question is, what to do about it.

The dealer was supposed to have comped a coolant change last year. Now, I'm sort of doubting it got done.

So... Are there any clues to get the needle to stay at 1/2 way, or maybe a needle width above 1/2. Anything higher than that just feels hot to me.

Should I change coolant? Any sort of cleaner? Any special instructions for changing the coolant? (I'm a old time VW / Porsche guy. I've only had water pumpers for the past 20 years, they still seem pretty new to me)

Thanks for any clues.

jnc.....

99 E300
99 boxster
70 914/6
03 Jaguar S type (hers)

Is the climate control system on at this time? If on, the aux. elec. fan should come on as well to stabilize temp. You might have a weak pressure cap. Very seldom are they tested and/or replaced. Might have wrong percentage of coolant to water ratio also. Keep in mind, given what you've said it is NOT hot.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Search air-conditioning threads for the procedure to put the 210 climate-control pushbutton unit into current-sensor mode, and read the value for the auxiliary fan. Ensure that it is running when the panel shows that it is getting input.

A quick test is to press and hold both AUTO buttons for >10 seconds, with the key in position 2. This starts the fans at full speed. Holding them for >10 seconds again or turning the ignition off cancels the test.

You can test the aux fan operation with key in pos #2 by holding both "auto" buttons for 10 seconds. Fans will engage full speed.

Am a little confused concerning how hot yours is getting. The halfway mark is 80c, the unlabled hash mark is 100C and then comes 120C. So...is yours running at 90c or at 110c?

You can confirm coolant temp while driving via the CC. Press and hold rest for 5 seconds with CC on. Use auto buttons to toggle to item #6. Mine is in F.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

You may also have a sticking thermostat, and when you get a chance, you might want to change it. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Since it is fine even driving around town, I doubt that the thermostat is faulty.

Either the mechanical fan clutch is weak, the electric fans aren't running, or the poster doesn't know how hot they get after this kind of use. The thermostat doesn't even open completely until 94C.

The plastic impellors from the water pumps on these cars are prone to breaking.

Changing the coolant is very easy, just disconnect both hoses from the radiator, let it drain, refill, massage the hoses to get the air out, and Bob's your uncle.

Ok... good information so far. I wasn't aware the t-stat wasn't fully opened until 94C. I'll run the climate control tests as suggested.

I'm not reaching the 100C line, but I'm closer to it than not (meaning just more than 1/2 way to the 3/4 mark) when I think it's 'running hot'. (keep in mind, it was only 82 degrees yesterday, for the those who say 'that isnt hot) If it's over 90C when it's 82, what'll it be when it's 100 outside? That is what marks my concern.

The fan cluch seem good. (based on what I know) Maybe I'm just overconcerned. After all, I had a Merkur that had cronic bad fan clutchs, and a Catera that had a 100C thermostat, and 7 electronic fan speed combinations that none of them kept the temp below 7/8 up the white part of the guage. I just sort of wish that normal, means middle, instead of above middle.

Thanks for the ideas....

So... A little time has passed, and now the ambients are higher.

I have a little history on my temps now....

Yesterday, I saw 200. (after a heat soak, and some intown driving, it stayed at 200)

Usually, it's in the 180's. (highway driving)

191 seems pretty easy to get to. (in town driving)

What about 200. Too hot? Or, just warm enough for the current conditions.

While my fan clutch works.... I suspect it is weak. I can hear the fan roar, but it doesn't roar for long, and the temp guage just sort of stays on the high side.

What are those in C? I do know right-off that 200F is under 100C.

I see 100C under certain conditions. Coming off the highway to a stoplight, for example.

Your redline is 120 or so.

100C would be 212F (212-32 X 0.555)

The temps you posted seem very typical to mine in hot weather. We had a couple of 100F days last week. During those times mine iwll run at 85C on the freeway with AC on and then climb to approx 95C in stop and go city driving. My aux fans seem to come on right about 95C. Between stop lights the temp drops as speed increases.

The highest I ever seen mine is 208f (98C); that was stop and go up a long incline on a 107F day.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)