87 300 E -The temp has dropped to the high 30s here so I have had to use heat. It takes several more miles/minutes of driving before the heat comes on. Could this be anything other than the thermostat? Where exactly is it located and how easy to replace? Is there any particular brand that is best and do all the gaskets come with it? Thanks.

This could be perfectly normal and expected...

I think there is a temperature sensor in the coolant that keeps the blower off in heating mode until the engine coolant reaches 50C (just above your 40C gauge line) so don't start replacing thermostats just yet.

I guess I was not specific enough. Last year in cold weather it took perhaps 3-5 minutes for the heat to come on. Now it takes 8-10 minutes in cold weather.

Well heat is determined by coolant temp so start there. How long does it take to get to 60 degrees? How long to 80? If this is taking a really long time then the thermostat could be stuck open causing the coolant to flow continuously through the radiator, causing the engine to warm up slower. The thermostat is there to help the engine warm up more quickly by bypassing the radiator so it will not cool the coolant. Then as the engine reaches temp and the coolant is above 87 degrees the thermostat opens, this keeps the coolant at or around the thermostat temp. Unless of course the air outside is too hot or you are idling to long and the coolant is not cooling below the thermostat's set temp. Either way, if it is stuck open then of course the coolant heats up slower and thus the heater takes longer to have warm fluid passing through the core.

Or it may be a vacuum pod bad or leak inside causing the vacuum element in the blend air section to not open properly or hold open enough. This is of course assuming that the coolant is coming up to temp in time and a good functioning thermostat. And also assuming that the heater valve is not stuck closed or malfunctioning as well.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....

Thermostats are cheap. Be sure to get a Wahler 87 degree along with a new sealing ring. Installation is dirt simple. Follow the upper radiator hose from the radiator to where it attaches to the thermostat housing. Remove the three 10 mm bolts from the casting. You do not need to remove the bolt in the center of the casting. Lift off the casting to expose the thermostat. Note that the existing sealing O ring will be stuck to the removed casting. Pay attention to the orientation of the old thermostat and put the new on in the same way. Put the sealing ring over the thermostat, then put the casting back in place and tighten the bolts.

I just did this on my '92 due to a lazy thermostat that was sometimes not keeping the running temperature at the proper temperature.

Hope it helps,

Steve

you may need to replace the ACC mono valve. i had similar problem and replacing mine cured the problem.

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1989 300TE

Hi;
Whatever the cause of delayed heat, your Benz is designed to produce heat almost instantly from cold. Within a 1/4 - 1/2 mile I can feel heat. Fastest heater of any car I have ever owned. Always been so and the same for other 124 owners I have talked with. Probably the same for other models of Benz.

Thanks Steve

lizem100,

While you're replacing the thermostat, consider replacing radiator hoses if they're original / not pliable. Especially the upper one. That piece broke on my W124 once, leaving me stranded. The replacement part was a better design, with a gentle bend built-in for more flexibility.