No thermostat? - Page 5 - PeachParts Mercedes-Benz Forum

#61 07-27-2006, 12:09 AM

Quote:

Originally Posted by blueranger

the coolant flow diagram shows the back of the thermost being closed and the front of the thermost being opened and thus allowing this circulation craig is taking about... but going back to hands on... all the thermostats i see are either closed or open... so the diagram must be wrong.

Yes, blueranger, Mercedes-Benz has been making water cooled cars wrong for the last 80+ years.

blueranger · #62 07-27-2006, 01:28 AM

"Let me try myself to explain to you in as few words as possible:
When the engine is cold, the front (radiator) is closed and the rear (bypass) is open. Allowing all water to return to the waterpump and back to the engine in a closed circut.

Between 82 and 93.9*c, the front and rear (being fixed as one shaft, move together) move to change the flow ratio between radiator and bypass to maintain 82*c."

the difference between you and me is that you are a theoritical mechanic where as I actually have a thermostat in my hand right now.. since i put them in and take them out regularly....i will say this in as few as words as possible. "when the top of the thermost is clossed the bottom of the thermostat is closed as well.."

So I am not saying mercedes is making vehicles wrong... I am saying your diagram is wrong.... that thermost will not in 1 million years open on the top and close on the bottom...when its opened the flow is open on the top and the bottom... and when its closed its closed on the top and the bottom... so your diagram with an arrow at the top is wrong... when it is closed the water circulates through the car heater coil...

#63 07-27-2006, 01:43 AM

Quote:

Originally Posted by blueranger

(theoretical) So I am not saying mercedes is making vehicles wrong... I am saying your diagram is wrong.... that thermost will not in 1 million years open on the top and close on the bottom...when its opened the flow is open on the top and the bottom... and when its closed its closed on the top and the bottom... so your diagram with an arrow at the top is wrong... when it is closed the water circulates through the car heater coil...

Ok Mr. rent-a-cop. I've been an active diesel mechanic (As in, paid to diagnose and repair diesel's for a living.) for 4 years. I know how to read a dang diagram, I know how thermostats work, I know how mercedes designed these engines to run, and I know that you are TOO CLOSED-MINDED TO LEARN.

The way you describe the thermostats operation is that the two ends MOVE AWAY FROM EACH OTHER. That's not how it works. They are fixed ON THE SAME SHAFT. When one end is FULLY CLOSED, the other IS FULLY OPEN.

The mercedes FSM's diagram is NOT wrong, you just don't know HOW TO READ IT.

Somebody near him, please give him a heavy-handed *itch-slap for me to knock some sense into his head.

redbaronph123 · #64 07-27-2006, 05:52 AM

just from my experience..

my 617 NA runs at around 82 degrees all the time in summer and reaches a peak of 90 degrees on hard runs. I dont have any thermostat. I'm not worried on heavy driving on flat roads, but when i do some driving on uphill climbs, my temp goes to 100.

On very cold nights, my temp drops to 75 degrees. Though it looks good seeing a cooler engine temp, i do think that this poses a problem (like a poster here mentioned about carbon build up as well as bad MPG ??). I've been running my car that way for 4 years, got that car that way.

Though I dont really have much problem other than worry about the temp at uphill climbs or at cold weather, I still wonder whether I should bring it back to the original configuration of having a t-stat.

EDIT PART: oh yeah.. my A/C is on most of the time.

t walgamuth · #65 07-27-2006, 06:36 AM

and yet another person living in a tropical climate, who doesnt need his heater and who doesnt drive on mountains or autobahns.

under a sustained heavy load it will overheat without a stat.

and in cold weather you just wont get any heat out of it unless you block the radiator. and then it will overheat under load.

you guys just arent going to outthink the benz engineers who have been using the bypass design for fifty years. if it didnt work they most assuradley would not keep using it.

thanks for posting the diagrams. they help a lot.

this is a subtle thing to understand. a lot of very experienced folks just dont see it.

but believe me, the benz engineers have it right!

tom w

#66 07-27-2006, 07:04 AM

Quote:

Originally Posted by ForcedInduction

The way you describe the thermostats operation is that the two ends MOVE AWAY FROM EACH OTHER. That's not how it works. They are fixed ON THE SAME SHAFT. When one end is FULLY CLOSED, the other IS FULLY OPEN.

That is correct, that is what the diagram shows, and I also replaced one last week in my 240D. It also appears that the bypass portion of the thermostat has a fairly weak spring that wound be pushed open by water pressure if the flow path through the radiator was too restrictive. I suspect that this design allows some additional bypass flow if the radiator is clogged. If the design allowed the flow to stop in the engine, and the heat was turned off, that would cause the water to heat up and result in pump cavitation, that would not be a good design.

t walgamuth · #67 07-27-2006, 07:25 AM

good point.

such subtilty in the design is typical of the thought that benz engineers employ.

tom w

#68 07-27-2006, 11:35 AM

Quote:

Originally Posted by Craig

That is correct, that is what the diagram shows, and I also replaced one last week in my 240D. It also appears that the bypass portion of the thermostat has a fairly weak spring that wound be pushed open by water pressure if the flow path through the radiator was too restrictive. I suspect that this design allows some additional bypass flow if the radiator is clogged. If the design allowed the flow to stop in the engine, and the heat was turned off, that would cause the water to heat up and result in pump cavitation, that would not be a good design.

Thank You.

GlennCraven · #69 07-27-2006, 01:27 PM

Quote:

Originally Posted by Brian Carlton

If you have no time for any of the above, you'll need to purchase and install a new radiator. The cost is about $300. and it's a 90% bet that it will solve your problems, especially if the radiator is original.

OK, but the car did NOT overheat when the '83 engine was in it, whether or not this is the original '83 radiator. ... It is the radiator that was in the car when the original (I presume original) engine was in the car, and that engine ran perfectly, temp-wise.

After the indie mechanic dropped the '85 mill in it (and left the temp gauge disconnected), the car began overheating.

Why would it most likely be the radiator under such a circumstance? Wouldn't it more likely be one of the cooling system parts on the '85 engine, i.e., the thermostat or water pump?

GlennCraven · #70 07-27-2006, 01:30 PM

Quote:

Originally Posted by blueranger

i have had thermostats fail open and fail closed...

most often overheating problems is becasue of a failed thermostat..
failing in the closed position....

I've been told this by two shadetree mechanics (one of them very capable, however) at work. They can fail open OR fail closed. ... Somebody here, however (don't remember who; too lazy to look) say that they only fail open.

I think a thermostat that sat idle for five years in the salvage yard motor very well might be rusted or fouled and thus be too restrictive to coolant flow. I can get a new thermostat for $15 or so and it's easy to replace, so I might as well do it. Then if I get the temp gauge reconnected at the same time, I can run it and see if replacing the thermostat helped keep it cooler.

Then I'll worry about water pump or radiator.

Brian Carlton · #71 07-27-2006, 01:33 PM

Quote:

Originally Posted by GlennCraven

I think a thermostat that sat idle for five years in the salvage yard motor very well might be rusted or fouled and thus be too restrictive to coolant flow. I can get a new thermostat for $15 or so and it's easy to replace, so I might as well do it. Then if I get the temp gauge reconnected at the same time, I can run it and see if replacing the thermostat helped keep it cooler.

Then I'll worry about water pump or radiator.

Folks chase the thermostat all the time and...........sometimes (1:50) it's the culprit.

It's cheap enough to change and see what you get. Better than changing the radiator, but I have my doubts that it will solve the issue.

Without a temperature gauge, how are you determining what's too hot and what's acceptable?

t walgamuth · #72 07-27-2006, 08:47 PM

excellent point.

tom w

85chedeng300D · #73 07-27-2006, 09:39 PM

Quote:

Originally Posted by vahe

A follow up on my post No.7, want to make it clear that I DO NOT at all recommend the removal of a functional thermostat, if it is not broke do not mess with it, but in my case I was faced with number of thermostats that remained shut after several hours of driving, the mechanic experimented with three different thermostats, all three refused to open up under normal driving conditions, so the choice was clear, I was forced to remove the thermostat. This all happened while I was in Washington State and the local MB shop that worked on my car was specialized in older MB’s like mine, they were doing cooling system service work including installation of a new radiator, flushing the system, hoses etc. A few months later I drove back to Houston, about 2300 miles, no cooling problems. While stationed in Washington State I did considerable weekend driving in the Cascades, lots of mountain passes etc, no cooling problems.

Houston based MB dealer has only one type thermostat for this car, if there are lower temp. thermostats available from another source, I would like to try them on my car, if you all give me name/contact information.

The fact that it was even suggested to drill holes around the thermostat to make it work, is a clear indication of MB design screw up with this particular item on 240D engines.

Vahe
240D 77/350K

Did you "BURP" the system? It seems like air is present inside the cylinder head and engine block which doesn't allow the hot water to completely soak the thermostat and trigger it to open.

When you get a chance, I would suggest that you reinstall the thermostat and fill the cooling system through the heater hose attached at the firewall end of the engine until the 50/50 mix overflows on the expansion tank or in your case, a 240 D, on the radiator filler neck.

vahe · #74 07-27-2006, 10:31 PM

"Did you "BURP" the system? It seems like air is present inside the cylinder head and engine block which doesn't allow the hot water to completely soak the thermostat and trigger it to open."

I was standing next to the car as the tech opened up the stat housing to see why it was not opening and coolant started to spill all over, so the stat was fully submerged in the liquid.

At any rate I would like to try installing a tsat again if I can find one that is designed to open up at a little lower temperature, any mail order supplier?

This was a very informative discussion, I learned the pros and cons of not installing a tsat in 616/617 diesel engines. One thing is clear, these engines are truly bulltproof, would you dare drive a E300 96/99 without a tsat?

Vahe
240/77 350K

hartley · #75 07-28-2006, 05:51 AM

Vahe......You have hit the nail on the head ,it's nearly always air in the system (on engines with the early type thermostat housing ) In my experience they always run hot after changing coolant because of air entrapment,thermostats seldom fail,they can fail of course ,like anything else ,but very very rarely .however there is a easy fix to this problem,make up a fitting to your garden hose and fill the radiator from the bottom,making sure to open the vent on top of thermostat housing.This system is used on Scania trucks ,and hey presto no more overheat....cheers