running hot, radiator? - Page 2 - PeachParts Mercedes-Benz Forum

Kajtek1 · #16 06-12-2015, 08:49 AM

Citric acid can help only so much so at one point you might want to replace old radiator.
I keep statistics and somehow each time MB owner comes with overheating problem - he is using Zerex. Just think about it.
Than most of MB have electric fans kicking in at 95C, so if the engine goes above that, check the fan as well. Don't remember if 85 has one, but I drove one in California mountains and it did not overheat.

funola · #17 06-12-2015, 09:14 AM

Quote:

Originally Posted by 240dddd

.......I may also try running temporarily without a thermostat to see if that has any affect.

FSM specifically warns against running w/o a T stat. T stat is a bypass design, w/o it, engine WILL overheat.

vwnate1 · #18 06-12-2015, 09:15 AM

So then ;

What's the ' Bees Knees ' for coolant in an old OM616/617 engine ? .

TIA ,

BTW : no 'stat is death on engines because it creates hot spots in the water jacket..

funola · #19 06-12-2015, 09:28 AM

Have you verified that your gauges are accurate with IR thermometers? Another thing which is easy to do is check the resistance of the sender (at the same temp) against another sender (that is known to be good).

Did you feel all the hoses and their relative temperatures as the car warms up from a cold start? If you know the flow path, it can tell you a lot where the blockages (if any) are.

Yesterday was 90F around here and I drove my 85 300D with AC on, city stop and go traffic, viscous fan clutch and shroud removed, so the only fan running was the AC aux fan (which was on the whole time), temp gauge was a steady 92 C.

Edit: running Zerex G05 coolant

Quote:

Originally Posted by 240dddd

Hi,

My 85 300D creeps up to 100 degree Celsius mark when the ambient temperature starts getting above 70 degrees Fahrenheit. I noticed it last summer during my commute; on warm to hot days the gauge would get up to 100c, particularly if I went up a hill. Once going down hill it would drop back down to about 80c after a few minutes.

During the fall and winter it runs steady at 80c. I've owned the car for ~4 years and don't remember it having summer temp problems earlier than last summer. The 240D I owned previously also seemed to run steady at ~80c even on hot days.

Here's what I have worked on recently (in iterations, trying to determine the problem):

changed thermostat - no change in running temps
performed a citrus flush - no change in running temps
replaced water pump - no change in running temps
replaced fan clutch - no change in running temps

So what is left, the radiator? Or are my expectations of running at a steady 80c incorrect? I want to eventually get the A/C working but don't want embark on that journey until I get a handle on the running temps.

thanks

rocky raccoon · #20 06-12-2015, 03:29 PM

for a minor "overheating" problem, first replace your radiator/expansion tank cap. Worked for me and certainly inexpensive enough to try particularly if it has never been changed.

vwnate1 · #21 06-12-2015, 03:39 PM

Quote:

Originally Posted by rocky raccoon

for a minor "overheating" problem, first replace your radiator/expansion tank cap. Worked for me and certainly inexpensive enough to try particularly if it has never been changed.

?? a pressure radiator cap does nothing to prevent overheating ~ all it does is raise the boiling point of plain water by 3° for every pound of pressure .

Bad radiator caps only allow coolant loss .

Left Coast · #22 06-12-2015, 04:10 PM

Quote:

Originally Posted by vwnate1

?? a pressure radiator cap does nothing to prevent overheating ~ all it does is raise the boiling point of plain water by 3° for every pound of pressure .

Bad radiator caps only allow coolant loss .

A bad radiator cap may not prevent overheating, but running at 100c is not overheating. A leaky cap may allow the coolant boiling point to drop to nearer to that temp. So while running at 100c is not really all that terrible, especially if it only happens on hard uphill runs, it's not so good when combined with a system that isn't holding pressure.

Quote:

Originally Posted by Kajtek1

Citric acid can help only so much so at one point you might want to replace old radiator.
I keep statistics and somehow each time MB owner comes with overheating problem - he is using Zerex. Just think about it.
Than most of MB have electric fans kicking in at 95C, so if the engine goes above that, check the fan as well. Don't remember if 85 has one, but I drove one in California mountains and it did not overheat.

Hardly surprising that most MB owners use the Zerex formula, since it's what MB recommends. Does your data also show whether or not those cars ran with other coolants prior to being filled with Zerex, and for how long?

240dddd · #23 06-12-2015, 06:13 PM

I was under the impression that the aux fan is only supposed to come on when the A/C is running so I haven't done any work to troubleshoot the aux fan (since I never have used the A/C). However it seems that it is in fact supposed to come on if the engine gets hot enough, and I do not think I have heard it turn itself on before.

Shortsguy1 · #24 06-12-2015, 08:26 PM

Quote:

Originally Posted by vwnate1

?? a pressure radiator cap does nothing to prevent overheating ~ all it does is raise the boiling point of plain water by 3° for every pound of pressure .
...

I don't follow your logic. As you said, a pressurized cooling system has a higher boiling point than a non-pressurized system (assuming all else is equal). So how do you conclude that it does nothing to prevent overheating? Your car can reach a higher temp before overheating (aka boiling) occurs if you have a pressurized system, so it does a HUGE amount to prevent overheating. Most of our caps are 1 bar or 1.2 bar, so using your approximation, that buys me an additional 45 F of coolant temperature rise before overheating occurs.

vstech · #25 06-12-2015, 08:31 PM

Well.... an additional 45 degrees before steam occurs in the engine... not 45 degrees before overheating occurs...

Shortsguy1 · #26 06-13-2015, 12:56 AM

vstech-
I genuinely don't understand the difference. When someone uses the term "overheats", I thought that was the same as "coolant boils over"? You know... the hood up on the side of the highway with steam coming off of the radiator cap. My owners manual for my 220 says that you can run up to 250F for short periods of time without concern for damaging the engine. Zerex G-05 boils at 265 (50/50 mix, 1 atm rad cap), so I guess I assumed that as long as you don't boil the coolant, no "overheating" has occurred. Is this assumption wrong?

ah-kay · #27 06-13-2015, 01:12 AM

Cooling happens when coolant is still in liquid form. Once it boils, gas is not a good transfer of heat so it is possible to damage the engine. It is because heat will be very localized inside the engine. A pressurized cap raised the boiling point of the coolant to keep it in liquid form to give you a safer margin of error.

Actually a pressurized cap does not matter that much if you have a good efficient cooling system. I have been running all my OM603 engines on much less rating than spec with no ill effect. Disclaimer - It is only me as I take risks with my cars PM/Spec all the time.

240dddd · #28 06-13-2015, 02:07 AM

I got under the car tonight and unplugged the aux fan then ran 12v to it directly from the battery. Much to my surprise the fan started right up, although it seems off balance or something is bent because the fan blades are hitting the aux fan shroud supports on the evaporator side making quite an annoying sound.

I pulled the fan off to investigate further and there was about fistful of debris trapped between the fan body and evaporator, some of which is stuck in the evaporator fins. I'm guessing there is at least some debris stuck between evaporator and radiator too, but it is pretty hard to see into that space.

If I have time this weekend I'm going to pull the radiator off and see what I find. I'm also going to troubleshoot the aux fan from the fan back.

Any tips are appreciated on the aux fan, I've researched a bit on this site but am still unclear as to how the aux fan is wired and what turns it on (i.e. is it just he A/C or also engine coolant temps)? It looks like the plug for the fan comes out from underneath the car on the front driver side, but I'm unsure where it goes from there. I know at some point it connects to the a/c system on the passenger side.

Mxfrank · #29 06-13-2015, 06:14 AM

On most benz applications, there are two fan switches and two relays. One switch is a pressure activated switch located in the A/C reciever drier. It will cause the fans to come on through the low speed relay when pressure is too high...300psi in most versions. The second is a switch at the engine water outlet that causes the fan to come on at high temperature...acutally, at too high temperature, anywhere from 100c to 110c, depending on model. There is a relay corresponding to each switch. For low speed, there's a ceramic reisistor, usually somewhere on the left side of the engine compartment.

Overheating means boiling over, not simply running hot. Running without a cap won't cause the engine to run hotter, but it will allow it to overheat sooner.

Kajtek1 · #30 06-13-2015, 11:09 AM

Quote:

Originally Posted by Left Coast

Hardly surprising that most MB owners use the Zerex formula, since it's what MB recommends. Does your data also show whether or not those cars ran with other coolants prior to being filled with Zerex, and for how long?

Such records usually are "not available"
I can only suspect that someone who saves $5 on better coolant now, could save $7 before and run "green stuff"
I bought 1987 300DT about 5 years ago and it was filled up with green stuff.
I flushed and switched to MB coolant, but radiator does not perform the best.
Just drove it yesterday with 100F outside and the engine wold run 95C on the freeway, while in slow traffic it would go to 105C.
It is overheating in my books as on cold days it would keep 78C.
It is OK for now, but would I be in idling on desert with 114F, the boil over is very likely.
For the record, MB does not recommend Zerex - it is accepting it.