monovalve?
 

Don't mean to sound like an idiot, but what and where is the monovalve?

I haven't really done any work on the climate control system and since it is apparently very complex I don't really plan to (other than this I suppose). Thanks for the help!

It is on the firewall, passenger side, in the engine compartment. It is "L" shaped, usually brown plastic, has a heater hose attached at the bottom and left side. There is an electrical connector at the top. The valve is electrically closed, blocking coolant flow through the heater core. When power is removed, it opens and allows maximum coolant flow, therefore max heat. Disconnecting it takes the ACC out of the picture, as far as heat regulation is concerned.
Picture: http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1EH0TL2AI1HW1DJPDR&year=1983&make=MB&model=300-CDT-001&category=R&part=ACC+Mono+Valve
My thinking is if you don't get max heat with the monovalve disconnected, you must have a problem with coolant flow or level. That aside, I will not be surprised if a new coolant bottle cap solves your problem.

I think your best bet for an infrared thermometer is on e-bay.

I found this one pretty quick at a reasonable price:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=50974&item=7506611104&rd=1

There are quite a few others in the category "infrared thermometer".

Of course, you can also verify the situation if you simply remove the thermostat.

If the temp drops back to 75°C. or so, then the thermostat is probably doing the proper job and the gauge simply reads a bit high.

Thanks!
 

Thanks for the advice on both the IR gun and the monovalve.

I wasn't sure if the cap would make that much of a difference...I know it cools somewhat better when pressurized, but hey, that would be great if it could dramatically change things.

If still running hot after monovalve disconnect, radiator replacement, cap replacement, certainly will get thermometer and make sure gauge is accurate.

Thermostat?!!!
 

So I took out my thermostat and did the test where I run it and see what the gauge reads. I took it out for a 25-30 minute drive and drove at about 55-65 mph. The temp rose to 60C and stayed there basically irregardless of my speed (slight fluctuations of a few degrees, but nothing major).

So does that mean that both my thermostats are bad??? The odds of that seem astronomical.
Is 60C what it's supposed to run at sans a thermostat, or is my gauge reading high?

I guess I'll do the test in a pot of water, but I need to get a thermometer...

In the meantime I'm going to keep using the car without thermostat for the sake of the engine, unless anyone can think of a reason not to do this. Really what would prevent one doing this all the time (in summer, of course, and I know it would hurt diesel mileage)? Wouldn't it be better to run the engine colder anyways?

There really is no good reason to run it with the thermostat in the summer months, however, fuel economy will be slightly off due to the colder coolant drawing heat away from combustion.

Dr. Bert makes some compelling arguments to run these engines colder, especially in warm climates. Do a search on his name and read all about it.

Your issue is either the gauge or the thermostats. Nothing else can be the culprit.

I don't want to knock the sage advise by Dr. Bert, but if your talking about driving a diesel (OM617) on short trips with a cold (or no) thermostat this is not going to give the same performance (meaning acceleration) as an engine that has the proper thermostat and allows the engine to reach around 80C quickly.

Precombustion chambers need to get hot and the head needs to warm up to allow that in short trips a cold diesel is a sluggish diesel (compared to a hot one).
Is it reasonable to say that a cooler running engine will reduce some of the thermal breakdown in oil over a long period of time? Show me the data.
I advise against running without a thermostat unless for testing purposes.
BTW, wasn't herr Doktor referencing gas engines that had some high mileage figures, not diesels?

[QUOTE=83mercedes]

Also I could try putting in a different thermo if that one is bad, I actually happen to have one, but the one in now is a behr, not likely defective.

[QUOTE]


Take the thermostat out and test it the old fashioned way, on the stove. Get you a cheapy cooking thermometer and measure at what temp the thermostat opens. Or if you're lazy remember water boils at 100C, you want it wide open before that.

Also, I went through 3 bad ones from the dealer before finding one at Autozone that worked, so don't think "oh so and so made it, it must be good".

-Alan


EDIT: If this was already suggested, then kindly look over this. I just noticed there's more than one page to the thread :)

No Thermostat
 

Yeah, I may try getting a new one, but I would take the sacrifice in power if it means my enginge will last longer. I've got some other issues I need to worry about before rebuilding the engine.

The only thing is, would this cause a greater buildup in engine deposits because of unburnt combustion byproducts, or would this be acceptable?

Reid, he had a special set of circumstances whereby the diesel would have increased durability without sacrificing any other issues.

First, he is in a warm climate. The time to get the engine up to 60°C. is not exceptionally long, even without the thermostat.

Second, he does not run it on short trips. His commute is something like one-half hour IIRC, so the engine reaches its operating temperature, about 65°C. and remains there.

I'm not convinced that there will be a performance loss when an engine running at 65°C. is compared to an engine running at 90°C. Remember, the exhuast gas and charge air temperatures will be slightly cooler. This could result in slightly more available power.

He is quite convinced that engine wear is severely reduced when running cooler temperatures, either gasoline or diesel. I don't have the data, but, I've got no reason to doubt him.

I wasn't saying the engine wouldn't warm up eventually, and I realized Dr. Bert is in a warm climate (I flew over Bakersfield in a small plane and wow! the thermal inversion over that end of the valley is bad!).
If I drove around in the desert all the time I might also remove my thermostat! If I drove the grapevine every day I would take it out for certain!
I was more concerned with short trips, you know the 5 to 10 minute trips some of us take frequently to the store and to work if the commute is short.

For several years I noticed my '79 300TD with a rebuilt '85 engine was real sluggish when I first started off in the mornings, we are talking even with 70+ degree ambient temps. Call it the "cold diesel." ALDA tweaked with little improvement.
I also noted that the temp gauge took longer to move to the operating temp (83C) where the heater would come on. I lived with this situation without digging into it for almost 2 years, because I swap cars and frankly the W124 300D came into my life (can you blame me for not wanting to drive the 123 when the '87 is beckoning? :D )
One cold day this winter I began to wonder why the '87 and the other 300D's warm up quicker on my 8 mile commute. In the "cold diesel" I never felt heat, or just started feeling some warmth as I reached my destination. I thought perhaps the fact that I had a three row radiator in it was involved, it always ran cold since I put it together (new engine and radiator all at the same time) so I finally mentioned it to my friend, a decades experienced shop owner and he said the car should reach 80C quicker that it was and that my car would run better if it got up to 80 quicker. OK, then with this info I decided to install a new thermostat (Kuhlermeister or Kuhlermaster brand) well, lo and behold the engine warmed up in 5 minutes and the car had more acceleration sooner! The diffrence was really noticeable after all this is my work car, I drive it almost daily so I know it is better.
I can assure you the old thermostat was bad. It had odd scrapes on the center brass shaft, I believe it was galling and sticking, making the warm up period much longer.
I can't say whether a cooler operating diesel will last longer but if you improve on the life of the OM617 you are potentially talking of raising it from 500K miles (I learned that from all the Ebay ads, right!?) to something I won't live long enough to experience.
ONe more thing that I believe is that frequent oil changes is one reason these engines last so long, besides good design and the forged iron head. I have seen two of my friends with Hondas and small Toyotas start buring oil at around 150K miles to the point they had to get rid of the cars. I looked at one of them and the EGR and PCV stuff was plugged with hard crusty carbon build up. I think that the small oil filters were part of the reason for premature engine failure but both instances they were not changing oil frequently and of course it was Dino oil. Oh no I am not steering this into a Oil thread. Forget what I said about Oil. this is a thermostat thread! ;)

I certainly agree with you there. I never take these two for a 5 or 10 minute trip. That's what a gasser is for. :D

No Thermostat, Good Results
 

In Florida in Spring/Summer/Fall (they're all pretty much the same season....summer), I'm talking temperatures of usually high 80's to high 90's every day. Also, I've been driving it around with no thermostat in at all, only the seal ring, and it reaches 60-65C in very little time at all (granted, my cooling system is also functioning sub-optimally). And that's with NO THERMOSTAT!! Dokter Bert is only advocating drilling a hole in the thermo so it is open full throttle all the time.

It does seem like an appealing fix to thermostat problems (in the summer), and it will force you to change your coolant often when you put the new one in for winter.

And yes, any performance decrease caused by a slight drop in combustion (definitely not significant with only 15C difference) would probably be outweighed by a cooler turbocharger and hence denser air intake.