High Engine Temp! Need Help Asap Guys! - Page 4 - PeachParts Mercedes-Benz Forum

stephenson · #46 06-24-2002, 09:18 PM

Another $0.02 worth ...

My 350 SDL just went through a bout of running hotter than normal after I changed out the coolant pump and the viscous clutch ... both had developed a bit of wobble from shot bearings.

Normal fill with 50/50.

Immediately following this I noted the temp rising to 105C very quickly - actually running over 100C while cruising at 75 mph with AC on ... it had never done this before! So, at this point, what had changed?

1. Coolant mix - yes, but how far off do you have to get with ratio in order to account for this much change? i.e. what if you ran 100% coolant ... would it run 100C instead of 82C in same load?

2. Viscous coupling - yes, but it was new ... possible to get a bad one? Yes, but mine was still running hotter than normal at high speeds with lots of ram air.

3. Coolant pump - yes, but if it wasn't leaking, and the impellers were close to the same, it would not be likely.

Baffling. So, I put it off for two weeks - couldn't stand it any more.

This weekend I changed out the viscous coupling again and changed the tstat, too. Old tstat opened and closed when boiled on the stove - rather an ancient test that I understand is not suitable for this tstat.

Am now running the same temps as before ... at 75 mph on 98F day (it was hot today) with AC on. During high load conditions, like going up long grade or in stop and go traffic at 98F, it would predictably creep up, but never hit 100C (during last hotter than normal period prior to change of viscous and tstat it would roll right up to 105C in 70C weather with AC). Something else I noticed, but did not expect, is that following work this weekend, it now runs to 82C much faster, usually within a mile after crank up in mid-60F temps.

What changed?

1. Viscous clutch - yes, but same but as before. I would liked to have waited and done this later, but once I dumped the coolant, I didn't want to waste another load of MB coolant. If it had been the viscous clutch, wouldn't the car have behaved normally with ram air flow?

2. Thermostat - yes. I believe this is what failed. Question is - why now? Was it related to having drained the coolant completely? Is there a chance something occurs to an old tstat when the coolant is left out for a few hours or days? Don't know, but this is the only rational explanation.

Good luck on the 560. I would:

1. Change the tstat and see what happens. Run water after you do it in case it isn't the problem. Don't run the water long term, but a few days likely won't hurt too bad.

2. Not change the coolant pump - pretty binary with these, I think.

Please keep us up to date - I KNOW these cases drive ya nuts!

jsmith · #47 06-24-2002, 10:44 PM

stephenson,
thermostats tend to stick as they grow older and are slower to open and close. maybe your maintenance procedures aggravated it. my thermostat was making the temps swing from 78 - 100 (<100 only because i have the cooling mod), so i changed it. now it's pretty constant at 90 - 95 in summer heat, with A/C on and stop & go traffic.

DJNEWK2 · #48 06-25-2002, 10:38 AM

My baby's still acting up and even after the fan clutch change, still shoots up past 110! She's just fine at highway speeds (steady 80-82) but just as soon as I take her off of the exit ramp, it shoots up and especially when I'm sitting at a light, the coolant is coming from the overflow tank and drains onto the pavement.

I've purchased MB coolant and not going to add it until this is fixed. I've been just driving with my 6 coolant jugs of water to replenish her when she cools off (the aux fan kicks in and when I shut her off, I leave the key on so it won't go off until it cools down) and I'm ready to leave for my next destination. None of the temps went up like this until AFTER I changed my coolant and have had drama ever since!

I just noticed last night that after we came off of the highway and I shut her down in the driveway, I popped the hood and saw that the hose to the expansion tank was being filled with some water that was pushed from the top of the radiator.I felt through the fan to the radiator and followed the direction of the fan with my hand on the radiator and from the right bottom of the radiator heading in a circular motion (with the fan) noticed it was cool to the touch and as I made my way to the top heading to the left it got extremely hot that I couldn't keep my hand on it. the top of the radiator was also very hot. I can't remember, but what does it mean as far as if the vents are hot/cool to the touch. should it be cool or hot after such a ride considering the ram air effect?

Although its brand new and not even been in the car a year yet, I'm now thinking it may be a radiator/circulation issue. Any opinions on this? How would I be able to check this?

Billybob · #49 06-25-2002, 11:32 AM

I have not yet completely diagnosed my 603 diesel overheating issue but I did learn a little something in the process so far.

If you have not yet found the exact location of your coolant leak on your 126 chassis, check out this leak that I found in my coolant system.

http://www.peachparts.com/shopforum/showthread.php?threadid=33244

I'm sure that any leak will prevent the system from operating at the required level of pressure so I would think you have to determine if the system will hold pressure and if not the exact location of any pressurized leaks first.

#50 06-25-2002, 12:40 PM

If you want to check your rad to see if it is plugged (which by your description it maybe) Remove the shroud from the rad on the fan side so the entire inside face of it is open to touch. Take off the the bottom rad hose (since your car is filled with water only already) and plug the opening on the rad with a cloth fairly tight (it will leak a little but is OK for this test. Disconnect your top rad hose and get yourself one of those plastic flower 2 gallon watering container with a spout (about $1.99). Fill the watering container with real hot water and put a piece of hose on the spout and put the other end of the hose into the top rad hole.Fill the rad with the hot water. Then run your hand over the entire surface of the rad on the fan side. The temperature should be the same all over the rad -if you feel cold spots or spots that are much cooler - you have a plugged rad - don't care if it is new or otherwise. If it is plugged you are halfway there to removing it to take to a rad shop for cleaning or recoring or to replace it. If the rad is partially plugged no amount of ram air or fan speed will stop the temp from climbing. Keep me posted.As an aside - I have worked on cars for 10 years now and have learned the hard way - just because a part is new - don't ASSUME it is not defective - have wasted a lot of troubleshooting time because I ASSUMED the new part was good. The best troubleshooting is still logic and common sense - and of course the old expert - experience - which you will have when this problem is solved! - Keep smiling - you'll get it!

JimSmith · #51 06-25-2002, 01:16 PM

DJNEWK2,

I agree that new parts are not always as they should be, and I would check the thermostat on your car again. The thermostat controls the flow coming from the hot engine (hot water) and directs some or all of it to the radiator. In an MB it also has a side that controls cold water flow from the radiator, and mixes the hot from the engine with cold from the radiator to maintain an even, controlled temperature from one end of the engine to the other. It also avoid thermally stressing the engine in the winter when the car warms up and the thermostat first opens.

So, if the thermostat is not working as it should, it can restrict flow from the radiator. The thermostat housing normally allows flow to the radiator, and when the engine is cold, it offers a bypass route through the thermostat to the water pump inlet, and the thermostat blocks flow from the radiator. This speeds up the warm-up process. When the engine heats up the bypass flow is restricted and the flow from the radiator is enabled. In the cooling system maximum thermal capacity operating mode, the thermostat blocks the bypass line completely and fully enables flow from the radiator, forcing all the coolant from the engine flow through the radiator before returning to the water pump inlet.

If both moving plates in the thermostat are not free to move through their full strokes, it may restrict the return flow from the radiator when, based on coolant temperature it should be enabling greater flow of cooled water from the radiator. Or, it may always allow bypass flow. In either case the hot water going into the radiator at the top will be nice and cool, or at ambient anyway, at the bottom of the radiator as it slowly makes its way to the outlet.

There should be a thermal gradient from top to bottom (inlet to outlet) anyway (or you are not removing any heat), so a cooler bottom (outlet) of the radiator is perfectly ok and by itself not a sign of something being amiss.

Good luck with the issue. Many have struggled and in other threads on the subject, changing viscous fan clutches and/or thermostats seem to help. Jim

edited for clarity

DJNEWK2 · #52 06-25-2002, 02:48 PM

Since I've changed the expansion tank, it no longer leaks around the base of the cap anymore...it now leaks from the overflow in the fenderwell. So the radiator SHOULD have cool spots on the fins?

#53 06-25-2002, 02:55 PM

When I did the hot water test on mine it was the same hottness all over. For the time it would take - I'd do the test and confirm or eliminate the rad as a culprit.

JimSmith · #54 06-25-2002, 02:58 PM

tkamiya,

I am not familiar with the location of the overflow tank, and any provisions the system has for venting when the pressure rating of the cap is exceeded. I figure it is possible to lift that cap just on temperature alone if you see a rapid increase in temperature indication that goes near the red zone.

The indicator on the dash has a lag time and it not sensing the highest temperature in the engine. So, it is feasible that the pressure in the system is near or at the cap's relief set point.

Overall the cooling system is pretty complex. Our interactions with it, as owners and maintaining it, are pretty limited, by design. Checking the cap is good idea though as the loss of pressure will eventually lead to loss of coolant and then serious overheating. Jim

sunil190e-1.8 · #55 06-25-2002, 03:29 PM

my 190 e which has a 1.8 litre engine used to run hot in traffic and at idling,the temp gauge would creep up to 120 degees on the temperature gauge.--my engine has an electro-magnetic clutch type fan which is supposed to cut in at 95 degrees if working properly-i replaced the cooling fan switch which is on the cylinder head and this has solved the problem and normal gauge behaviour has returned.

do the 560 engines have an electromagnetic type auxiliary cooling fan-if so irt would be worth checking the cooling fan switch out.

the only other time i have seen a bmw 525 overheat like yours is when the t-stat snapped shut and another time an audi ,5cylinder ,in which the radiator core was blocked-changing the radiator cured it.the odd thing was the radiator appeared totally normal from the outside but the inner tubes were blocked.
a

JimSmith · #56 06-25-2002, 04:05 PM

DKNEWK2, and moedip,

The radiator works by spreading the hot water out over a relatively large surface area of a thin metal barrier that has a surface area enhancement treatment, fins or a corrugated metal filler between water channels, to maximize contact with air. The air is heated by the transfer of heat in the water that in turn heats the metal of the fins or corrugated stuff.

The hottest water in the radiator is at the inlet from the engine, and the coolest water in the radiator is at the outlet. If the flow rate is very slow, the water will spend enough time in the radiator to reach a temperature approaching that of the air when it reaches the outlet. So that will give you a thermal gradient of hot to cool from one end of the radiator to the other. If there is not thermal gradient, the system is not working. You might as well replace the radiator with a short hose.

The test moedip described flows water into the radiator faster than the normal coolant flow rate. If, under those conditions you see a hot and cold spot, it will most likely be from the flow pattern (all the flow going in one area instead of over the whole radiator or being excluded from a couple of areas). The flow pattern abnormalities can be due to restrictions from junk collecting or chemical deposits, like hardening of the arteries, in the water passages in the radiator, or pinches in the coolant passages. Since the flow is not prototypical the results must be interpreted carefully. You should give a few seconds to let air vent and so on.

In any case, the moedip test quickly fills the inside of the radiator with hot water, and before it can give up a significant amount of energy to the air, you can feel the distribution of flow as areas of the radiator that are warm. Warmer areas have had more hot water flow by, and cooler areas less. I would still expect the water that entered first and ended up travelling farthest in the radiator to be cooler than the hot water entering last.

I hope that helps. Jim

stephenson · #57 06-25-2002, 04:15 PM

If temp runs OK at speed, this would appear to mean the radiator is working effectively enough to keep temperature at minimum (tstat tries to keep a minimum temp, right?) ... so, how can it be the radiator?

Have you changed the tstat? If not, give it a try ... what do you have to lose?

DJNEWK2 · #58 07-17-2002, 09:48 AM

Hey guys...its been a long time and I've been outta town unable to get to my baby until day before yesterday. Well, I changed out the thermostat (with the bleeder valve at the top/right position like the old one that looked pretty good mind you) and took her on the road.ONCE AGAIN, 80-82 degrees around town for about 15 minutes but when I got her on the highway and exited, 110+! I've also had it tested for pressure and its okay so far. Today on the way to work, the same thing but now she stays at 100+ on the highway. I'm wondering if I should replace this "new" radiator with the old one I kept to see what happens because other than the broken neck, the car still ran at 80-82.

Another question I have is: Is the fan supposed to be able to spin freely when you shut the car off? I ask because on some of my other cars I've had, the fan doesn't move at all unless the motor's running. I was able to move the fan freely as I felt around the radiator after shutoff which revealed the radiator being very cool on the right side (facing car) and then hot as hell when running my hand toward the left side by the hose. Also, when I had the car running, I'd squeeze the upper hose to see if I could feel water rushing through and did not feel it at all. The top of the radiator is also hot to the touch.Is this a matter of the radiator being clogged and what could clog it this fast (its only been in the car a little under a year) ?

I'm wondering if I should change out the pump although there is no leaking or squeaking/noises. Would it be safe to replace that old radiator with a broken neck in order to have my other one checked or should I just suck it up and replace it (again but with a Behr)? Any help is appreciated and thanks for the replies so far in my plight to correct this.

Mike Richards · #59 07-17-2002, 10:06 AM

DJNEWK2:

I'm not going to pretend that I've digested every word of this thread - actually - I've read little except for a couple of posts you've made on page 4.

You mentioned some spots on the radiator being cooler than others. You mentioned temps were ok B4 changing out the radiator - you changed because of a broken neck.

Seems to me the radiator might be the problem. Is it a Behr? I personally wouldn't use any other brand. If the neck is just cracked in a spot, but will still hold a hose, try reinstalling the old radiator and see what happens. I'm not suggesting this as a permanent solution, but if the old unit is usable for a "test", why not give it a try?

I too had an overflow out the expansion tank problem. Thought it was the t-stat. Changed it. Still overflowing. Turned out to be a weak seam in the tank - wasn't holding pressure. I realize that you may have addressed this already - again - haven't read every word in this 4 page thread.

My 2 cents.

DJNEWK2 · #60 07-17-2002, 10:58 AM

I would definately only use this as a test...I was just wondering why a perfectly good and functioning radiator would all of a sudden fail unless it got clogged while draining it and refilling it? Who knows, but this whole thing is driving me nuts

Thanks

Alan

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