Verify correct engine coolant temp after cleaning/upgrade - PeachParts Mercedes-Benz Forum

aldaeron · #1 11-13-2012, 04:06 AM

Hi All,

I know there are many threads about engine coolant temperatures, but I wanted to verify I have everything correct so I can stop compulsively watching my temp gauge when driving.

I have a 1980 300 TD (non-turbo).

Thanks to some good advice here I realized something was wrong and did a full overhaul on my coolant system.

- Old ACCII servo was leaking. Removed and replaced with simple manual valve so I have some heat and no more leaking coolant.
- Removed all coolant hoses and flushed with hose (including block)
- Ran Zerex radiator flush through system then flushed 3X with water
- Ran diluted citric acid through system then flushed 3X with water
- Ran diluted baking soda through system to stop acid then flushed 3X with distilled water
- Replaced as many hoses as I could find online with brand new ones.
- Replaced water pump with new one (found a good deal on Amazon!)
- Added new Zerex mixed 50/50 with distilled water
- Burped system
- Found some cheap hose clamps were used, replaced all hose clamps and burped again

I think everything is working correctly but I have a few nagging questions:

I seem to see a consistent temperature of 90C on surface streets and the highway, but it has become quite cold here in Colorado so it hard to be sure how much cooling I am getting from the outside air. It will sometimes creep up towards 100C in bumper to bumper traffic but seems to correct itself pretty quick. Is this an acceptable temperature? From my official MB repair manual the thermostat is partially open between 80C and 94C so this seems to make sense.

Since I had some leaks from bad hose clamps I have been feeling various parts of the system after I stop driving to make sure there is even heat distribution (i.e. coolant is properly pulling heat out of the engine to the radiator). The one strange thing I keep finding is that the lower radiator hose and the lower portion of the thermostat housing it attaches to is typically cold to the touch (feels like the air temperature). The bottom portion of the radiator also feels cold. Often the top half of the radiator and the top radiator hose are nice and hot. Is this normal? I know the hot coolant enters the top of the radiator, but I am surprised to see all the heat dissipated by the radiator before getting to the bottom. My concern is that the new water pump is not moving the coolant around properly or there is still a bubble somewhere in the system preventing coolant from moving around correctly. I have done a few burps and I believe all the air is out.

Thanks in advance for helping put my mind at ease.

-matto-

oldsinner111 · #2 11-13-2012, 05:33 AM

bottom portion of radiator should be cooler.I use vinegar as a flush one gallon to water and drive car 1 hour with thermostat out
then I flush till water smells fresh,then install thermostat.I refill with Sierra antifreeze at 100%.No water,your good to go for ten years or 500,000 miles.

Govert · #3 11-13-2012, 05:40 AM

During normal operation the temperature should be between 80 and 94 degrees C. High ambient temperature and/or high load on the engine could increase the temperature above 94 degrees. Also when driving slowly, there is not much air cooling, so the temperature will increase. The fan clutch will slip less if the coolant temperature is above 90-95 degrees C, so the air flow is increased above 90-95 degrees C.

Your 90-100 degrees C is a bit high. That can be a faulty temperature sensor and/or temperature gauge, they aren't precision instruments. Sensors are prone to fail over time. Can you check the coolant temperature with an other thermometer?

The fact that the bottom part of the radiator is cold would indicate that the thermostat is only partially open and that would imply that the temperature sensor/gauge isn't showing the correct temperature.

If the water pump is new, it is unlikely that it will not pump enough water, unless the paddle wheel isn't tight on the axle (unlikely) or if the drivebelt isn't tight enough. Did the water pump house look good?

Air in the system can happen, although it is my experience it will be pumped out after one or perhaps two drives (showing itself as a reduced coolant level). Did you keep track of how much coolant went into the system? It has to be close to 11 liters (approx. 2.9 gallon), i.e. about 10.5 liters because there is always a bit of residual coolant in the system (mostly in the heater core). Is the coolant level OK?

jay_bob · #4 11-13-2012, 08:20 AM

OP says they are in Colorado.

What is your altitude, higher altitude = less dense air = less heat transfer than at sea level.

I know above 3300 feet we have to derate our equipment to compensate for this. IIRC you lose about 5-10 % at 5 k feet...

tip · #5 11-13-2012, 11:14 AM

I don't see a replaced t-stat on your list. With all that work you did (impressive BTW), a t-stat should be a replaced. There's a few threads that mention drilling a few small holes into the t-stat to allow extra coolant past it. I would look there first.

Quote:

Originally Posted by oldsinner111

I refill with Sierra antifreeze at 100%.No water,your good to go for ten years or 500,000 miles.

Why no water? H20 has 2x the heat capacity of 100% antifreeze (ethylene glycol).

PackerEdgerton · #6 11-13-2012, 11:26 AM

Quote:

Originally Posted by oldsinner111

bottom portion of radiator should be cooler.I use vinegar as a flush one gallon to water and drive car 1 hour with thermostat out
then I flush till water smells fresh,then install thermostat.I refill with Sierra antifreeze at 100%.No water,your good to go for ten years or 500,000 miles.

I'm not familiar with Sierra antifreeze, but assuming it is normal Ethylene Glycol (like Prestone), then Ethylene Glycol is less efficient at thermal transfer than water. Yes, it has a higher boiling point and contains anti-rust and various stabilizers, but it is less efficient at removing heat. Therefore, the temp would be higher since the liquid is less efficient at removing the heat.

The OP didn't do this, but I would suspect that if he did, he would get a higher temp reading.

Sincerely,

Packman

Mike D · #7 11-13-2012, 11:56 AM

Oh goody! An antifreeze thread.

*opens bag of popcorn and sits back to enjoy*

cho · #8 11-13-2012, 03:28 PM

Quote:

Originally Posted by tip

There's a few threads that mention drilling a few small holes into the t-stat to allow extra coolant past it.

this can not be solution to overheating IMHO.

.

cho · #9 11-13-2012, 03:34 PM

Quote:

Originally Posted by aldaeron

Thanks to some good advice here I realized something was wrong and did a full overhaul on my coolant system.

what was reading before the overhaul?

btw your nick is very WOW like

.

aldaeron · #10 11-14-2012, 11:00 AM

I did replace the T-Stat, T-Stat gasket, Water Pump Gasket and Engine Block to T-stat housing gasket.

The new Bosch water pump looks fine and the shaft looked nice and tight. The belts are tightened per the Mercedes spec using a Gates Krikit I & Krikit II to verify force as best I could.

I am aware that the dash sensor can drift over time and the sensor wears out. I have an Omega TC-K-NPT-G-72 which is a 1/4 NPT thermocouple I can screw into the block. I have not yet screwed it in to check the sensor accuracy (I will post back results when I do). I did learn that the engine coolant sensor thread is a 1/4 - 18 (AKA 1/4 NPT) thread. That info is nowhere to be found on forums. I may replace the stock temp sensor with the thermocouple permanently and wire up and calibrate a new circuit to the dash gauge.

I have been driving it more and see a consistent reading of 90C on the dash gauge. The fact that is nice and steady in all driving conditions is reassuring. I will use my thermocouple to see what the real temp is in case of sensor or gauge miscalibration.

Govert: What is your typical dash reading? What is the "ideal" temperature for a properly operating 617.912 engine?

Thanks again for all the replies! You guys are great!

-matto-

tip · #11 11-14-2012, 12:15 PM

Quote:

Originally Posted by cho

this can not be solution to overheating IMHO.

I agree, I don't think its the solution to overheating. But, for getting the temp down that last 5 or so degrees after everything else in the cooling system has been sorted, I think is reasonable.

cho · #12 11-14-2012, 02:29 PM

Quote:

Originally Posted by aldaeron

I did replace the T-Stat

-matto-

culprit !
very often guys have problems with new t-stats

test it to be sure
.

Jareb · #13 11-14-2012, 02:43 PM

Quote:

Originally Posted by cho

culprit !
very often guys have problems with new t-stats

test it to be sure
.

I had this just happen to my car also. Car ran at steady 85-86 C. Did a coolant change and new thermostat and the car now runs at 93-95 C. The cause is the new T-stat. Mine is a 80 degree Behr. I ordered a new Wahler. I'll post back if there is a difference.

aldaeron · #14 11-14-2012, 06:38 PM

I used a Behr 80C, brand new.

I did test it in boiling water and it did function. I was not checking the temp that it opened at, just that it was not DOA.

I have an Alstrom Imports brand that I got at Napa. I may check that out. I am going to hook up my thermocouple first to get an accurate temp reading. I did not change the temp sensor or check the calibration of the dash gauge.

cho · #15 11-15-2012, 02:04 PM

.

yeap first things first,..if problems persist make sure t-stat fully opens at 90C (94 max).

cheers

.