Differences in thermostats - Page 2 - PeachParts Mercedes-Benz Forum

t walgamuth · #16 01-07-2007, 01:24 PM

an 80 degree stat is designed to maintain 80 degrees. it will begin to open at some lower temp and will be completely open at 80.

tom w

t walgamuth · #17 01-07-2007, 01:26 PM

Quote:

Originally Posted by stephenson

Good inputs - however, consider that there are many, many folks who report having tstats that don't work right. They can be "designed" by real engineers (but, in this case, the design work was done about 80 years ago, I think ... recently simply a lowest cost production issue), but still respond well to custom mods that could not be done to meet the price points in large scale production.

This variety of tstat has stood the test of time pretty well - think about them being virtually unchanged for decades - when everything else on the engine has changed substantively. What if tstats had evolved the same way - imagine a sensor based electric system that measured water in 3-5different places, also using inputs from other thermal sensors and position sensors to anticipate loads so that as you start up a hill, the tstat opens in advance of the load -maintaining temp +/- 1 degree ALL THE TIME. If it is gonna be electric, why not make the coolant pump electric, too (I think this is already in the works with move to higher voltage systems) - and then the pump could work with the sensor system and the tstat to completely control thermal issues without belt drive - it could even operate off the battery when the belt does through itself .... pretty cool!

go right ahead and do whatever you want.

but i would not if it were mine. it is not rocket science, but the system is designed to work all together and it works very well when all components are in good working order.

folks who have problems have one or more elements that is not working properly. modifying the stat will not help, imho.

tom w

tangofox007 · #18 01-07-2007, 03:24 PM

Quote:

Originally Posted by t walgamuth

an 80 degree stat is designed to maintain 80 degrees. it will begin to open at some lower temp and will be completely open at 80.

tom w

The service manual for the 617.95 engine states that an 80 degree thermostat should begin to actuate at 80 degrees and not fully actuate (main valve fully open and bypass valve fully closed) until the temp (at the thermostat) reaches 94 degrees. So it would seem that the thermostat that maintains the coolant temp at 80 degrees is the one not performing to specification.

Relying on the coolant temp gauge to evaluate thermostat performance is further complicated by the fact that the thermostat and temperature sensor are not co-located, at least not on the subject engine. When the thermostat is fully actuated, it is "seeing" coolant that has just exited the radiator, which is arguably cooler than the coolant to which the temp sensor is exposed.

In short, having an expectation that the indication on the temp gauge should equal the thermostat rating is not well grounded.

t walgamuth · #19 01-07-2007, 03:36 PM

well, i wont argue with the factory shop manual.

but i will say in my experience which spans over thirty years, an 80 degree stat has resulted in a normal operating temp of very near 80 degrees unless the engine is working under severe conditions in which case the temp will go higher.

i apologize for any misinformation about when it opens fully that i apparently disseminated.

tom w

softconsult · #20 01-07-2007, 04:57 PM

I'll just throw in my experiences. This comprises around 75K on a '90 300E, 140K on my '92 300E, 10K on a '93 E320 and currently 6K on a '97S320.

All engines had '87 degree stats. The '90 and '92 were M103's temperature gauge was pretty much always one needle width above the 80 degree mark.
I don't remember the '93 particularly, but think it was the same. Definitely not at what would be 87 degrees if it were marked.

When I got the '97 and had put several thousand miles on it, I noticed that it was running right at the 80 degree mark. I swapped thermostats between '92 and '97 and sure enough the '97 ran hotter. Stuck or sticky thermostat. Swapped back and then replaced with Dealer 87 degree unit. It now runs at what would appear to be proportionally higher level on the gauge.

So I conclude that as long the indicated temperature is somewhere in range above the 80 mark and below the 100 mark and is consistent day to day, then I'm happy.

Steve

t walgamuth · #21 01-07-2007, 05:07 PM

your experience seems to indicate that in the cars you have owned the t stat sees higher temps than the guage sender.

on the cars that i am more experienced with, the 123s and 115s , they must be closer. they have 80 degree stats and run around 80.

tom w

softconsult · #22 01-07-2007, 07:07 PM

I was on K6JFR's website looking at his section on Water Wetter. He describes assuming that his water to coolant ration should have been correct given that the car had been serviced at the dealer. He found it to be incorrect.

I have the same scenario. Car had it's 90K dealer service at 99K and coolant was changed. Think I will buy the little Prestone ratio tester and check it out.
Maybe the coolant to water ratio is too high, which would cause the engine to run slightly hotter than I was used to in the 124's.

Steve

Steve

123euroowner · #23 01-07-2007, 08:01 PM

Which stat will make the motor run warmer...my 617 seems to run much better at an elevated temperature..and which makes it run coolest

engatwork · #24 01-07-2007, 08:13 PM

Engineers may design them but I am not convinced that the actual product is a very exact device. I have seen t'stats all over the place versus what they are stamped. Right now I am running one stamped 90dC in my 240D (winter thermostat) and it will get to 100dC in traffic which is fine for keeping the inside of the car toasty when sitting at a traffic light.

t walgamuth · #25 01-07-2007, 09:34 PM

i have always used german made stats.

i have found them to be remarkably accurate.

if you are reaching 100 at idle i would suspect a problem.

tom w

nhdoc · #26 01-07-2007, 10:16 PM

I just bought a new MB OEM thermostat from the dealer for my newly acquired 300CD Turbo. The old one was stuck open and the car never got above 50C. The new one runs it at 90-95C constantly.

The radiator is brand new and since I know the cooling system is in good enough order to keep the car running at or below 50C all day long I can say conclusively that this new thermostat is keeping it running at these temps by design in my opinion.

I didn't look too closely at it for a makers mark or temp reading but the car does not overheat...it never goes above 95C and seems to run fine at that temp, so I am leaving it alone...FWIW I think there are some that keep them at 80C but I do think the MB factory model intends them to run 90-95C now for some reason.

Shorebilly · #27 01-08-2007, 05:59 AM

Quote:

Originally Posted by tangofox007

The "extra flow" should have the opposite effect on a bypass system. The added flow would be from the radiator.

Now for the $64,000 question. Is an 80 degree thermostat supposed to maintain a coolant temperature of 80 degrees? Or does the thermostat temperature rating describe the temperature at which the thermostat begins to actuate? At what temperature does an 80 degree thermostat completely actuate?

I just changed my thermostat to one that I purchased from my MB dealership, because I wanted exactly what was designed for the application......so I have an official MB thermostat, marked for 80 C.....

The thermostat is designed to open at 80 C to regulate the water entering the block for 80 C.....your temperature gages are reading a sensor in the cylinder head at approximately 90 C.....this is a normal 10 C temperature rise from water entering the block at 80 C and exiting at 90 C....

For those of you without an MB service manual.....there is a little arrow stamped on the edge of the MB thermostat.....this arrow points up.....

The thermostat that I removed was an AutoRad made in West Germany...had a slightly different construction and did not have an arrow.....

SB

t walgamuth · #28 01-08-2007, 09:20 AM

Quote:

Originally Posted by nhdoc

I just bought a new MB OEM thermostat from the dealer for my newly acquired 300CD Turbo. The old one was stuck open and the car never got above 50C. The new one runs it at 90-95C constantly.

The radiator is brand new and since I know the cooling system is in good enough order to keep the car running at or below 50C all day long I can say conclusively that this new thermostat is keeping it running at these temps by design in my opinion.

I didn't look too closely at it for a makers mark or temp reading but the car does not overheat...it never goes above 95C and seems to run fine at that temp, so I am leaving it alone...FWIW I think there are some that keep them at 80C but I do think the MB factory model intends them to run 90-95C now for some reason.

it sounds like you got a higher stat. maybe an 87, i think maybe that is a common one.

tom w

nhdoc · #29 01-08-2007, 10:05 AM

It had no arrow on it that I remember seeing...but I think those are only on the ones with the little vent holes and this one didn't have that either. If it doesn't run any warmer in the summer than it does now I don't plan on doing anything more with it...if, for some reason it runs warmer I will pull it and look at it again to make sure I didn't miss anything during the installation.

tangofox007 · #30 01-08-2007, 10:20 AM

Quote:

Originally Posted by Shorebilly

The thermostat is designed to open at 80 C to regulate the water entering the block for 80 C.....your temperature gages are reading a sensor in the cylinder head at approximately 90 C.....this is a normal 10 C temperature rise from water entering the block at 80 C and exiting at 90 C....

Exactly. When the thermostat main valve is open, the temperature on the gauge should always be higher than the temperature at the themostat.