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  #1  
Old 01-06-2003, 09:39 AM
mattsuzie
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Brrrr......Heat is no longer hot.

In my 420, the air coming out of the heater is no longer hot when going down the highway (over 60 mph). I look at the water temperature gauge and it reads 60 C. When I drive around town it will go to about 65F and eventually 70-75F if I drive for a long time around town. It will go back to 60F if I go back on the highway.

When I turn the car off, and say go to the store for 15 min and when I come back into the car, and turn it back on, the air is hot, but just until I go > 60 mph again. The air has a better chance of staying warmer (but not hot) longer if I drive at <50 mph around town and in traffic. It absolutely turns unwarm when >60.

I have a few theories.

1 - Bad thermostat? 60 C seams pretty cold for the water temperature. I thought it should run between 80 to 100F?

2 - Bad water/heater controller valve? I do not know what you call it, but I think there is some kind of valve that can go bad, get stuck or something and that can cause hot water not to flow properly (Not sure).

3 - Bad electronic controller? Unlikely, but thought I would throw it in because you never know.

I checked and replaced the fuse anyway.

Any thoughts? I am thinking it is #1 or #2.

I drove up north and froze my @#$@#$%@# off.

Brrrrrrr
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  #2  
Old 01-06-2003, 10:31 AM
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Join Date: Jan 2002
Posts: 165
sounds like thermostat, remove and replace, see what happens. cheap and easy fix.
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  #3  
Old 01-06-2003, 11:09 AM
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I would agree that a new thermostat, and more likely, the monovalve repair kit will solve your problem...


Jay..
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  #4  
Old 01-06-2003, 11:27 AM
Potomac German Auto
 
Join Date: Mar 2002
Location: Frederick, MD
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aux water pump ?
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  #5  
Old 01-06-2003, 12:16 PM
mattsuzie
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Thanks guys. Will get thermostate ASAP.

What is the monovalve? What is involved in the "monovalve repair kit?"
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  #6  
Old 01-06-2003, 12:23 PM
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Quote:
Originally posted by mattsuzie
Thanks guys. Will get thermostate ASAP.

What is the monovalve? What is involved in the "monovalve repair kit?"
It's basically a heater control valve.. If it's not working, or stopped up, no hot water will enter the heater core..
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  #7  
Old 01-06-2003, 02:54 PM
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Join Date: Sep 2002
Location: Denmark
Posts: 412
I had the exact same problem. -Engine temp 60 C. and penguins running around in the cabin.

I replaced the thermostat and my engine temp. went up to 85-90 C. and i can now toast a loaf of bread on the dashboard.

$15 and ten minutes of work. Do it!

Freestyler
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  #8  
Old 01-07-2003, 07:45 AM
mattsuzie
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Just to make sure, to replace the thermostat, do I also need to buy a new gasket? If I have to buy a new gasket, is there a special adhesive I need to apply as well?
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  #9  
Old 01-07-2003, 09:13 AM
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Quote:
Originally posted by mattsuzie
Just to make sure, to replace the thermostat, do I also need to buy a new gasket? If I have to buy a new gasket, is there a special adhesive I need to apply as well?
No adhesive necessary.. The new thermostat should come with a new o-ring seal.. That's all you need..

Unscrew the three bolts..Pull he housing off.. Pull the o-ring off.. Pull the old thermostat out.. Put the new one in in the same direction as the old one.. Install new o-ring.. Yada Yada Yada. Don't break the bolts when you re-tighten.
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  #10  
Old 01-14-2003, 11:16 AM
mattsuzie
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The thermostat for a 300 SEL is as easy as pie, but the one for the 420 SEL (a V8) is not. You have to take a bit more apart and need some special tools in order to access the bolts.

After 3 hours, I gave up and had to tow it to a tech.

Will see how it performs today.
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  #11  
Old 01-14-2003, 09:45 PM
mattsuzie
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I needed a new thermostat and heater valve. The cars runs now at 82C and the heat is toasty warm.

The thermostat is pretty tricky on the 420.
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  #12  
Old 01-16-2003, 04:33 AM
mattsuzie
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I was just wondering. What is the ideal engine operating temp?

Can you cause engine damage without the theromstat, i.e, running the engine at 60C as opposed to 85C over the long haul?
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  #13  
Old 01-16-2003, 08:05 AM
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The ideal engine temp is between 80 and 100 dC but if it goes above 100 dC there should not be any problem as long as it drops back down when the aux fans come on. You do not want to run these cars without a thermostat.
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  #14  
Old 01-16-2003, 08:49 AM
mattsuzie
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I'd assume that the lack of a thermostat would cause it to run more ineffieciently, but could it cause signigicant damage to rings, pistons, etc. Just curious.
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