99 e300 td

i live in the socal areas and theyre alot of hwys that travel up long hills and mountians. the outside temp is also in the 100+. for the most part the temp is pretty solid at 80c for my driving except when i hit the hills. it seems that when im in boost things really get cooking. i have a new radiator, flush, thermostat...fan clutch.. so it doesnt seem to go past 95-100c. is there anything i can do to keep the temps more level? add an autometer guage? i get worried when i see the temp guage instantly start climbing when im driving 70mph and im out in the middle of nowhere.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

Try drilling a couple of small holes in the thermostat. It will take longer to warm up though. I have 2 thermostats that I use. One standard for winter driving and one with 3 holes for summer driving with the AC on in traffic. Your thermostat may be no good as well. That happens sometimes even with good German ones. Especially with the Chinese junk.

Check your expansion tank cap. Failure to hold pressure will result in your exact symptoms.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

im pretty sure the thermostat is good. i already have 1 hole in it for air burping. i can sit in traffic all day long with the a/c cranked and the temp wont budge from 80c. the only time it rises is when i climb hills..even with the a/c off. i mean its instant ..as soon as i start going into boost the temp goes up with it.

i'll get a new coolant cap and see what that does.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

Maybe it would be worth while looking beyond the cooling system. You have done just about all you can there. It is possible (though I hope not) that you have the start of a head gasket problem. It is only showing under load, are you getting a lot of pressure build up in the cooling system or small bubbles in the coolant? There could also be an issue with your IP set up, Too much advance under load. I have no experience with the exact motor in your car, my suggestions are general for most diesels.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I'm not sure there's reason to believe there's any problem. On both of my 300's (1991 and 1992), the temp climbs when under load (e.g. on long grade), especially with the AC on. I routinely see 100. I think aux fan(s) kick in at 105 or something.

More authoritatively, the owner's manual says this: "During severe operating conditions and stop-and-go city traffic, the coolant temperature may rise close to the red marking."

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

The problem is with unrealistic expectations. Expecting 80 degrees under demanding conditions is just that.

Agreed.

Additional load creates more heat. More heat raises the engine temperature and also opens the thermostat to allow more flow. There will be a temperature where equilibrium is established.........and it will be way above 85° degrees.

The only time to be concerned is if the thermostat is wide open (98° coolant temp.) and the engine temperature continues to climb. Even this scenario is tolerable provided the operator is cognizant of it and doesn't exceed 110°F. if there's a proper pressure cap and sufficient coolant concentration in the system.

The concern about elevated temperatures that approach 100° seems to be perpetual on the forum.........much of it ado about nothing.

even gas engines will climb some on reading up mountains.For my area I swap in a thermostat for summer with holes drilled everywhere.Both gas and diesel.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

ive never had a problem like this with any car i've had. i would expect mercedes to over engineer the cooling system to cool things down no matter what... especially not cooking the water during a casual drive up a gentle mountian grade. i get a little nervous when things arent under normal operations when im out in the middle of nowhere driving a car that probably cant be fixed on the side of the road..and when each repair does cost an arm and leg. i would be flippinng out if this was a new car and this was considered "normal"

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

There are plenty of new cars in which the normal operating temp is close to 100 degrees.

I guess what some of us are saying is that what you're experiencing isn't in any sense a "problem;" your car sounds like it's operating exactly as it was designed to operate. It simply behaves differently than other cars do. I'm convinced that, on both my cars, the cooling systems operate perfectly and I routinely see the temp climb to 100.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Start by confirming that dash thermometer is accurate. Infared thermometers are in expensive and can be used to test many things including proper functioning of thermostat and radiator.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

You've probably never owned a car which had a temperature guage which reads the actual coolant temperature. Asian manufacturers all use "idiot guages" which give the same indication across a wide range of normal operating temperatures. Mercedes does not - you have simply never before seen what actually occurs under the hood. The laws of thermodynamics apply equally no matter the continent from which the vehicle originated.

That's actually very interesting. I had always just assumed that Honda, for example, simply did a better job of regulating coolant temp. But the way you explain it makes perfect sense.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife