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.

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

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

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, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 178k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 75k 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, deutschland deutschland uber alles uber alles in der welt

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.

I just fixed my overheating problem with my 300SDL but it may or may be applicable to your car.

1) Change out the overflow tank cap with a new one. I bought a 20lbs one from Autozone for $5, so it is not that expensive to try. Try to sqeeze the radiator hose after the car is at temp for a while. The hose should be pressurized and should stay pressurized for a day, may be longer. This is normal. If the hose is not pressurized then the cooling system is not air tight, most likely a leaky cap.

2) Check the aux fan can go on high speed. I do not know your car but there should be a thermostat-switch near the top of the radiator hose. It may be 2 prongs or may be 3 prongs. That is the trigger switch for the fan to come on. On my 300SDL, it is 3 prongs and if I shorted the 2 prongs connector and the fan will come on. The third prong goes to a single connector is cut in at 125/8C to turn off the A/C I think. Your car may DIFFER.

3) You can get a lower cut-in temperature thermostat switch. My 300SDL is 105C rated ( grey color ) for the fan to cut in. I bought a 100C rated ( red color ) to give it a better safety margin as it has the #14 head.

Hope this help. Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Same thing on many domestic/American makes. The oil pressure "gauge" for example, pops to the same place in the normal range, if the oil pressure is normal, no fluctuation.

BMW figured this out in the late '70s/early '80s also. Customers would get together at club meets etc., notice that one car had higher or lower pressure than another, the guy with the lower pressure reading would start to badger the dealer for a repair. Changing to the idiot gauges solved the "problem".

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Gone to the dark side

- Jeff