Engine Temperatures - PeachParts Mercedes-Benz Forum

mach4 · #1 08-04-2012, 11:20 PM

I'm running an OM617.952 that I swapped into my 107 and have been working through the systems. As it stands, "normal" operating temperature is about 60C or a little less, with an ambient of around 80F. Normal driving doesn't make it move all that much. A hard pull up a 6% grade for 2000' will bring the temp up to 80C or maybe 85C at the same ambient. Dropping back down the grade quickly drops the temperature to 60C.

From everything I've read, with an 80C thermostat I should be reading 80-100C as "normal".

I'm going to crack open the thermostat housing next week when a new gasket arrives and I'm guessing I'm going to find no thermostat in there. I've got a thermostat that came with a housing I pulled awhile back and a pan test showed it opening properly right at 80C. I'll be swapping that one in.

Two questions
- any other conditions that would cause the low temp readings I'm seeing?
- about how much antifreeze will I loose when I crack the housing?

Thanks

sixto · #2 08-05-2012, 12:53 AM

If you're using the original temp gauge, are you sure it's compatible with the 617 sensor?

Sixto
87 300D^2

mach4 · #3 08-05-2012, 01:09 AM

Quote:

Originally Posted by sixto

If you're using the original temp gauge, are you sure it's compatible with the 617 sensor?

Sixto
87 300D^2

According to the info I've found for the sender applications, yes...

sixto · #4 08-05-2012, 01:20 AM

My 617 days are long ago. Can you stick a wire down the upper radiator hose fitting to feel for a thermostat? Might answer your question without as much coolant loss.

Sixto
87 300D^2

BoiseBenz · #5 08-05-2012, 01:47 AM

What does the thermocouple or IR gun show for head temperatures? Gauge/wiring/sender might be wonky.

mach4 · #6 08-05-2012, 02:12 AM

If, when I open the housing, there is a thermostat in there and it checks good, when I button it back up I'll put a different housing on that has a sender port - that way I can check things by just switching the connector. I've got a spare gauge I can test things with too. I will check the temp using an IR thermometer as well.

Thanks

qwerty · #7 08-05-2012, 10:19 AM

Quote:

Originally Posted by mach4

...when I button it back up I'll put a different housing on that has a sender port - that way I can check things by just switching the connector.

Would that sensor port be on the front (return) side of the thermostat?

Stretch · #8 08-05-2012, 11:32 AM

You'll loose minimal coolant at the thermostat - don't sweat it - it will be fine.

As for your temperature of 60 degrees it sounds like the thermostat is stuck open - or not there!

Even though you've thought ahead and got a compatible sensor etc I'd still check the coolant temperature independently. If you've got an infra red gun then they're great but a standard contact thermocouple + multimeter / glass thermometer will still work!

mach4 · #9 08-05-2012, 10:41 PM

Quote:

Originally Posted by qwerty

Would that sensor port be on the front (return) side of the thermostat?

Here's the thermostat housing that's on the car now. Note it has a place for a sensor to be drilled and tapped but none present.

Here's the spare one I've got with what appears to be a switch installed (markings: VDO 100C/95C 4.75 120C max 6-24v 100W 30/3/22 ) I'm assuming the threads would be the same for a temp sensor to be used just as a backup and verification.

It should give a decent reading as it would measure the temp of the coolant exiting the engine and entering the radiator, albeit on the downstream side of the thermostat.

mach4 · #10 08-05-2012, 10:51 PM

I've temporarily misplaced my IR thermometer, but I'm quite convinced that the temperature is acting accurately, predictably and logically like there is no thermostat (or it 's stuck open).

Took a 125 mile trip today. 60C driving on local roads to the the freeway. A 65-70mph pull up a 6% grade to 3000 ft peaked at 85C and immediately dropped to 75C on the level. Down a local grade, it went back to 60C, then up a long grade to 4000 ft at a slower back roads speed peaked at 82C. Then back down it ran between 65C and 80C depending on whether we trending up or down on local grades. Ambient was 85F pretty much throughout.

qwerty · #11 08-05-2012, 10:52 PM

Quote:

Originally Posted by mach4

It should give a decent reading as it would measure the temp of the coolant exiting the engine and entering the radiator, albeit on the downstream side of the thermostat.

Just one problem. It's not exposed to coolant leaving the engine; it's looking at coolant returning from the radiator. The 617 bypass thermostat arrangement is a bit different that the typical Ford or Chevy.

mach4 · #12 08-05-2012, 11:10 PM

Quote:

Originally Posted by qwerty

Just one problem. It's not exposed to coolant leaving the engine; it's looking at coolant returning from the radiator. The 617 bypass thermostat is a bit different that the typical Ford or Chevy.

Dohh - of course. I completely missed that. Yup, that bypass thermostat system is definitely different.

Thanks for pointing that out.

mach4 · #13 08-13-2012, 07:49 PM

I finally got around to opening up the thermostat housing to check on the thermostat, and here's what I found...

The PO cut the thermostat actuator right out of the housing. So my initial diagnosis and suspicions were confirmed.

I installed an 80 degree thermostat with a new gasket, and it is running at about 83C and goes up to about 90C on a steep uphill grade (95F ambient today).

Needless to say it runs a lot better with the proper setup.

gatorblue92 · #14 08-14-2012, 07:27 AM

Quote:

Originally Posted by mach4

I finally got around to opening up the thermostat housing to check on the thermostat, and here's what I found...

The PO cut the thermostat actuator right out of the housing. So my initial diagnosis and suspicions were confirmed.

I installed an 80 degree thermostat with a new gasket, and it is running at about 83C and goes up to about 90C on a steep uphill grade (95F ambient today).

Needless to say it runs a lot better with the proper setup.

I'm guessing that is the only way to fool the system into running without a thermostat since it is a bypass system?