Lowering Engine Temp? - Page 2 - PeachParts Mercedes-Benz Forum

mach4 · #16 05-20-2014, 09:15 AM

Quote:

Originally Posted by BenzTurbo

I can't imagine there is much torque converter slip past 2500 rpm unless the trans is in bad shape or you're pulling a trailer...

These are not lock up torque converters, so they constantly slip. Here's an experiment - pick a speed and note the rpms at steady state; then accelerate and note the rpms; then from the same speed decelerate and note the rpms. The difference between the high and low is the slippage range.

I have a trans temp gauge on my car and at 80 ambient I get about 150 level ground cruise, and if I go up a 6% grade for a bit it climbs to 180 or a bit more, so there is definitely some slip-to-heat going on, and that contributes to the heat load of the radiator.

A stand alone trans cooler would help, preferably if it were out of the wind stream of the radiator.

rscurtis · #17 05-20-2014, 09:56 AM

A gradual rise in temperature is indicative of a tired radiator. Spend the time to fix the real problem rather than try to re-engineer a cooling system that has worked for years.

I can't see an auto trans dumping that much heat into a cooling system unless it's on its last legs and ready to give up the ghost.

t walgamuth · #18 05-20-2014, 10:29 AM

Quote:

Originally Posted by Mxfrank

Diesels build heat under load, that's part of the issue.

The rest of the problem is that Mercedes designed these cars to have a wide variation in temperature, which I think was a poor design choice. Try the electric fan mod I posted, it's the simplest solution.

Sorry to disagree, but I think the cooling system works just fine if all parts are in good shape. I have no idea what is meant by the first sentence second paragraph....?

Mxfrank · #19 05-20-2014, 02:30 PM

Quote:

Originally Posted by t walgamuth

Sorry to disagree, but I think the cooling system works just fine if all parts are in good shape. I have no idea what is meant by the first sentence second paragraph....?

Mercedes engineered the Diesels to have a normal range of 80-100. Ironically, the internal design of the motor is called a "constant temperature" system, because when the thermostat is in it's sweet spot, it allows proportional flow between the radiator and the bypass to give precise regulation of inlet temprerature. Constant temperature is desirable for several reasons:

1) Water flows around the block continuously, redistributing heat from hot spots.
2) The engine operates at it's design temperature, which should be optimized for efficiency and emissions.
3) Steady temperature means steady pressure, which reduces stress on cooling system components.

However, the external controls on any Mercedes, specifically the fan clutch and electric fan switch, are designed to engage progressively only when temperature is beyond the thermostat's max travel point, 10-15C past it's set point. I think they did this to spice up the HP numbers, as the fans pull a fair amount of power. It's also worth pointing out that the thermostat lives at the bottom of the motor, but the gauge sensor lives at the top, which means you really don't know what's happening at the regulated inlet.

As designed, main fan won't come on until 95, and the aux won't come on until 100C or higher. The thermostat will end it's travel around 93 or 94. Coolant flow past the thermostat will not change proportionally to temperature at the extremes of it's range. So the there's a tendency to overshoot, and it's hard to get temps back down when the engine is under stress. And that assumes that the rube goldberg arrangement of thermoswitches and bimetallic strips, all in different locations and measuring different things, is in spec after 30 or 40 years on the road. I see no reason to save the fans. Progressive airflow should be initiated as the thermostat enters the final millimeters of stroke. That's why I use a 92C switch to operate the aux fans at low speed.

All that said, a coolant flush and blowing the dust out of the fins would be the best first step in diagnosing any cooling system.

t walgamuth · #20 05-20-2014, 03:46 PM

You have provided an impressive explanation of how it works, however I disagree with your characterization of the thermostat being located at the bottom of the system. On every mercedes I have had it is located right at the front of the head so it is reading the hottest coolant the engine has to offer. The temp sensors are normally located in the head iteself though sometimes I believe they are in the t stat housing.

As for designing it so that the temperature is held at a more constant temp, that would require more coolant around the hot parts of the engine increasing the weight and space occupied of the motor.

As for making the controlled temp hit a narrower band that will quickly become a non issue at the first long hill you hit as all the cooling devices will quickly hit their maximum capacity in any case.

In any case if the temp of the coolant is higher more btu's will be thrown off into the air increasing the cooling capacity of the system.

If your temp gets too high you just have to back off your throttle and speed, as you do with any vehicle.

That said, I see no great harm in installing a lower temp. sensor to activate your electric fan, but in doing so you will decrease your fuel economy.

I think the Mb engineers thought this all through very thoroughly and were not trying to Spice up horsepower ratings....what in a 240d.... from 68 hp to 68.25?

Mxfrank · #21 05-20-2014, 04:22 PM

Quote:

Originally Posted by t walgamuth

You have provided an impressive explanation of how it works, however I disagree with your characterization of the thermostat being located at the bottom of the system. On every mercedes I have had it is located right at the front of the head so it is reading the hottest coolant the engine has to offer.

No, it isn't. To find your thermostat, locate the lower radiator hose and follow it back to the block. Mercedes has been using this design since the early 70's. The advantage of a low mounted thermostat is that it controls inlet water temperature. This prevents the thermal shock which occurs when a top-mounted thermostat opens and cold water hits the bottom of the engine. What you see at the top of the motor is just an outlet tube, no thermostat there. But they do located some sensors there on some models.

Cool water from the radiator enters from one side of the thermostat, hot water from the bypass hits the back. The thermostat reacts to the blend of hot and cold temperatures. Because the thermostat is exposed to both extremes, it's designed to react slowly to temperature changes. Which is another reason why the temperature sometimes reacts oddly to changing conditions. It's not a bad system, but has some annoying quirks. It makes the excursion to 100 much to often for my taste.

uberwasser · #22 05-20-2014, 04:37 PM

Except that we are talking about an OM617 in this thread. That's what the OP's car has. On the OM617 the thermostat is located at the top of the engine, right up at the top of the cylinder head.

When you remove the housing, you find the opening from the cylinder head is right at its top edge. The thermostat is located just an inch or so from this spot:

Mxfrank · #23 05-20-2014, 09:16 PM

Nope. For at least 40 years, all Mercedes have some variation of the same constant temperature system, with the thermostat at the bottom. It's a pretty complicated casting, I've annotated a cross section for you. The tube going to the left in the photo is the inlet to the thermostat. Installed, it is fed directly from the lower radiator hose, the cool side of the system. The thermostat is located at the inlet of the water pump, and the water that passes through it goes from the bottom of the water jacket to the top. The passage from the head is separated from the thermostat by the bypass passage. The bypass directs the hottest water in the system to the back of the thermostat and back through the pump when the engine is warming up. It's closed when the thermostat is open. So although the thermostat may seem to be high up, it's actually at the bottom of the coolant path.

t walgamuth · #24 05-20-2014, 11:06 PM

Quote:

Originally Posted by Mxfrank

Nope. For at least 40 years, all Mercedes have some variation of the same constant temperature system, with the thermostat at the bottom. It's a pretty complicated casting, I've annotated a cross section for you. The tube going to the left in the photo is the inlet to the thermostat. Installed, it is fed directly from the lower radiator hose, the cool side of the system. The thermostat is located at the inlet of the water pump, and the water that passes through it goes from the bottom of the water jacket to the top. The passage from the head is separated from the thermostat by the bypass passage. The bypass directs the hottest water in the system to the back of the thermostat and back through the pump when the engine is warming up. It's closed when the thermostat is open. So although the thermostat may seem to be high up, it's actually at the bottom of the coolant path.

In my book when the thermostat is located at the top of the motor it is definitely up.

If you said the thermostat is at the end of the coolant path that would be accurate. But the end is not the same as the bottom which has an actual dictionary meaning which is not the same as the end.

The drawings attached are not very clear. Where are they from?

Shortsguy1 · #25 05-20-2014, 11:39 PM

Because mercedes uses their thermostats as a mixing valve, I think you guys are both correct. The water comes from the head and encounters the thermostat. If the coolant is cold, the water is routed back to the engine, bypassing the radiator. When the coolant warms, the water still comes from the head and encounters the thermostat, but now some of it is directed to the radiator. That water rejoins the flow at the other side of the thermostat, and heads back to the engine. When the coolant is very hot, the thermostat is wide open, forcing the entire coolant flow through the radiator. But under normal operating conditions, the coolant encounters the thermostat both before and after the radiator. So it is at the start and end of the coolant loop (or top and bottom perhaps?).

ArmchairRacer · #26 05-21-2014, 12:55 AM

I'll blow out the fins and flush the coolant. The fan appears to be working. If that stuff doesn't make a difference I might try the 75C thermostat mentioned earlier. Normally I wouldn't worry about building this amount of heat on a steep grade but I have to drive this grade every day.

cooljjay: I live just outside of St. George, Utah

cooljjay · #27 05-21-2014, 02:44 AM

Quote:

Originally Posted by ArmchairRacer

I'll blow out the fins and flush the coolant. The fan appears to be working. If that stuff doesn't make a difference I might try the 75C thermostat mentioned earlier. Normally I wouldn't worry about building this amount of heat on a steep grade but I have to drive this grade every day.

cooljjay: I live just outside of St. George, Utah

Ah I am right near kanab.....go to st george on occasion. Your in the same boat as me, we have to deal with altitude and elevation climbing steep hills. When I go into flagstaff, my temp will climb a bit till I reach the top because I am usually in third trying to keep 45/50mph up the hill.

I would avoid flushing the coolant system with anything besides water. This will break settlement free and can cause the radiator and heater core to plug.

And again, adding a 75 degree thermostat, is a band aid....you are just trying to mask the main issue.

Regardless of what other say, I highly recommend replacing the radiator. Its made of plastic, if the right zerek G05 coolant isn't used and the green stuff has sat in the radiator for who knows how many years it will eat at the plastic.

When I first got my 78 it would climb and I replace the radiator...then it would never climb over 85....it has just started climbing, being up here and climbing hills at altitude.

I also believe I know what pair of cars you bought.

uberwasser · #28 05-21-2014, 02:58 AM

Quote:

Originally Posted by Mxfrank

Nope. For at least 40 years, all Mercedes have some variation of the same constant temperature system, with the thermostat at the bottom. It's a pretty complicated casting, I've annotated a cross section for you. The tube going to the left in the photo is the inlet to the thermostat. Installed, it is fed directly from the lower radiator hose, the cool side of the system. The thermostat is located at the inlet of the water pump, and the water that passes through it goes from the bottom of the water jacket to the top. The passage from the head is separated from the thermostat by the bypass passage. The bypass directs the hottest water in the system to the back of the thermostat and back through the pump when the engine is warming up. It's closed when the thermostat is open. So although the thermostat may seem to be high up, it's actually at the bottom of the coolant path.

I think a clearer use of terms is needed. The top of something is never also the bottom. Just saying. The whole back and forth could have been avoided had you said "end" or "coldest spot" or something. Instead we find ourselves arguing semantics.

Mxfrank · #29 05-21-2014, 08:00 AM

Quote:

Originally Posted by Shortsguy1

Because mercedes uses their thermostats as a mixing valve, I think you guys are both correct. The water comes from the head and encounters the thermostat. If the coolant is cold, the water is routed back to the engine, bypassing the radiator. When the coolant warms, the water still comes from the head and encounters the thermostat, but now some of it is directed to the radiator. That water rejoins the flow at the other side of the thermostat, and heads back to the engine. When the coolant is very hot, the thermostat is wide open, forcing the entire coolant flow through the radiator. But under normal operating conditions, the coolant encounters the thermostat both before and after the radiator. So it is at the start and end of the coolant loop (or top and bottom perhaps?).

This is why I use the admitedly confusing term "bottom" Shortsguy has it exactly backwards. The thermostat doesn't directly control the flow path to the radiator. Rather, it controls the flow path to the engine block. It feeds water into the block from the bottom to the top. It's clearer on a 601, where the thermostat physically lives at the bottom of the motor, but no less true on a 617.

Maxbumpo · #30 05-21-2014, 08:28 AM

Quote:

Originally Posted by ArmchairRacer

I'll blow out the fins and flush the coolant. The fan appears to be working. If that stuff doesn't make a difference I might try the 75C thermostat mentioned earlier. Normally I wouldn't worry about building this amount of heat on a steep grade but I have to drive this grade every day.

Read the factory service manual for the citric acid flush procedure, which is the proper way to flush the entire cooling circuit.

You can test your thermostat in a hot water bath (pan of water on stove top) to make sure of two things: (1) it is opening at the correct temperatue and (2) it is fully open at the correct temperature. If you replace the thermostat, check the replacement for both operating conditions prior to installing, it is not terribly uncommon to get a bad thermostat right out of the box.

I would also recommend that you try a full synthetic 5w-40 or even a 0w-40 engine oil (Mobil 1 or Amsoil). Engine oil is not only a lubricant but also a coolant, and a thinner oil will flow more quickly and thus be able to carry more heat away from the engine bearings.

I do not recommend a cooler thermostat, and if the temperature does not remain above 110 deg C for an extended period, your engine will be fine. Remember, this is a compression ignition engine; it needs the heat of compression to ignite the fuel. If you install a cooler thermostat and deprive the engine of the heat it is looking for, your engine will be less efficient (worse MPG) and produce more soot (increased engine wear).