I have an '84 300D Turbo. I had it for two months and have now begun to stretch her legs. The thing is, the motor almost never gets above 80 on the temp. Thats with like 4 hours touring at 3000+ on the tach.

It has auto climate control. The blower works fine, but the heat coming out is not so hot at first, but enough to keep the chill out. After afew hours, the air is regular air temp, so I have to turn it off. No fog, but man my feet freeze after a while.

The car runs awesome, whats the deal with the air temp? Any ideas? Is it running too cold? I'm in MO, so its right around 20 - 40 F right now.

Check to see if there is a thermostat in place. My friends 300SD was running like that - never getting above 80 dC no matter how hard it was run and when I pulled the thermostat housing I found that someone had removed the thermostat.

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Jim

mine did the exact same thing. installed new bosch thermostat-
problem solved.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

My car runs at 80-85 degrees C also, depending on the outside temp. I thought this was the normal temperature. I get plenty of heat at this operating temp.

when i had the same symptoms the temp would never reach 80-more like the middle between 40 and 80. new thermostat instantly solved the problem.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

My friends car would barely get to 80 dC. Not getting up to temp is NOT good for a diesel or any other engine for that matter.

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Jim

The thermostats in the 300D's frequently fail in the open position. As others have indicated a new thermostat is the solution. Be sure to buy a good one because there have been lots of stories here about bad units out of the box from cheepo parts sellers. That should cure your no heat problem but if it doesn't you will likely also need a new monovalve core. Neither of these is very hard to replace and a search of prior threads should give you lots of detail on how to do it if you need help.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

You should get good warm air coming from the heater at 80c. Your main problem is with the monovalve that allows the hot water to circulate to your heater core. It is located next to the firewall on right side next to battery. It may need to be replaced, cost about $25. if you do it yourself.

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Gary
85 300D Ivory, 202,000
Beatus exsisto Jesu, verus et Deus verus Vir

80c is 176 degrees in US temp. I agree something is wrong with the heater cause 176 degree water is pretty hot.

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They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety. Benjamin Franklin, A.D. 1759

Roger
1975 240D
1986 560SL

My 84 is moody with the heat sometimes, I know my monovalve needs to be replaced. Sometimes no problems at all, other times it doesn't matter if the coolant is ~82, I still don't get much if any heat. When I drive slower the car runs about the same temperature, yet I get heat at slower speeds. This is an indication of a bad monovalve.

I don't drive my MBs enough when it is cold out so I really don't know how long it takes to warm up to around 80 normally, but this should give you an idea if your thermostat is bad or not. It seems like it takes at least 3 miles before the thermostat opens, then maybe another ~5 miles before it is warmed up. I may change the thermostat in my 84 this spring anyway, as I plan on changing the coolant as well.

~jm

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

to be very slow to build up engine temp when weather is COLD due to the amount of extra metal in the engine blocks that holds down heating of the coolant...thus the available heat to the cabin. Both my diesels run "cold" and are slow to heat in bitter cold weather.

You should get warm air once your car reches 50-60 Centigrade temp. Normal human body temp is about 37-38 degree C.
So you should feel the warmth for any temp above this. If at 80c you dont get heat you have one or both of the following 2 problems.

1. Bad monovalve.

or

2. Failed Auxillary water recirculating pump.

Check my previous post to test which one is it. Reach under MVK and recirculaing pump. I bet its your recirculating pump.

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles