116 sd overheating-can't find problem - PeachParts Mercedes-Benz Forum

bruiser · #1 11-09-2005, 06:19 PM

sorry about the length of this, but i want to provide all the possible details.

she kept overheating, so i flushed the coolant and replaced the thermostat (also bypassed the servo so i could have heat in the winter, but that is inconsequential to the problem). it is still not acting normally. temps will rise VERY gradually as i drive, not to overheating, but above the line between 175 and 250 (212.5?). i haven't let it get much higher, but i also haven't driven it more than 20 minutes at a time. the heater (which now blows hot-yay!) will relieve some of the heat, but once i turn it off it slowly rises again.

the thing is, the lower radiator hose is not hot. at all. upper radiator hose is hot and squishy. the top of the radiator is hot but the fins are only slightly warm (maybe just radiating from the metal top), and at the bottom, cold. there had been squealing from the front of the car prior to the initial overheating that i attributed to the fact that it was wet out and the belts were just slipping a little. this squeal has not returned, and the fact that there is no coolant leaking from the water pump leads me to think the water pump is ok, but i'm certainly not ruling it out.

air bubbles in the system after replacing t-stat? maybe. i don't know if i burped it properly (can't seem to find a definitive method to know when the air is all out), but i did it like a million times or so. there are no coolant leaks to be found.

should i take the t-stat back out and do a thermometer-water test on it, put it back in if ok, and see if that helps? can i test the radiator myself for proper flow? can i get a definite on the water pump in any way besides replacing it? i need to use this car for more than just driving around town, so the expertise here would be appreciated. thanks.

RAYMOND485 · #2 11-09-2005, 06:42 PM

1984 300d Turbo 135k
Pull The Top Radiator Hose And Add Water To Top Hose Air In The System, I Had The Same Happen After Changing The Radiator And T-stat

boneheaddoctor · #3 11-09-2005, 08:49 PM

Perhaps you are overdue for a citric acid flush....cured mine of it tendency to get way to hot climbing mountains....

Pray you don't need a new radiator.....Phil quoted $780 for a new one....and Nobody but Benz has ever supplied one for this model.

My trans cooler sprung a leak and I need to find a shop to re core it ...before I fork over for a new one....I have a spare but its 26 years old too....

BenQ · #4 11-09-2005, 09:12 PM

I usually fill the block before I put the thermostat in. Or I remove the temp. sending unit to give the air in the block some place to go while filling with coolant.
Couldn't hurt to test the thermostat.
Wouldn't rule out a plugged rad.

____________________________________
83 300sd
3 Fords
ase 6,7,8 certified mechanic

bruiser · #5 11-09-2005, 10:29 PM

thanks for the replies...

i pulled the top rad hose to purge any air from the system, but coolant just kept coming out of the radiator when i poured it in, so i figure, no more air, right?

anyway, took it out for a half hour drive, and temp never got above 200, but it seems to take a lot longer to get to operating temp than before all this started. boneheaddoctor, what is your normal operating temp in your 116?

also, when i got home there was a lot of pressure in the system, where there never was until this problem began. the coolant in the overflow tank was basically lukewarm, but the upper hose had a lot of pressure, and the tank hissed pretty bad when i opened it up. i'm thinking of replacing the cap, since it seems to be original and i've read a lot about that causing problems, though i don't know if my problems are symptomatic of a bad cap.

i'm probably going to recheck the orientation of the thermostat, i know i put it in facing the right way, but i didn't check the "arrow" to see that it was pointing up. don't know how much that matters, just trying to cover all bases here.

boneheaddoctor · #6 11-10-2005, 08:19 AM

Quote:

Originally Posted by bruiser

thanks for the replies...

i pulled the top rad hose to purge any air from the system, but coolant just kept coming out of the radiator when i poured it in, so i figure, no more air, right?

anyway, took it out for a half hour drive, and temp never got above 200, but it seems to take a lot longer to get to operating temp than before all this started. boneheaddoctor, what is your normal operating temp in your 116?

also, when i got home there was a lot of pressure in the system, where there never was until this problem began. the coolant in the overflow tank was basically lukewarm, but the upper hose had a lot of pressure, and the tank hissed pretty bad when i opened it up. i'm thinking of replacing the cap, since it seems to be original and i've read a lot about that causing problems, though i don't know if my problems are symptomatic of a bad cap.

i'm probably going to recheck the orientation of the thermostat, i know i put it in facing the right way, but i didn't check the "arrow" to see that it was pointing up. don't know how much that matters, just trying to cover all bases here.

I think I was around 180 -190 on the guage would take a 10 mile steep mountain grade to hit 200.. take a flashlight look into the radiator where the upper hose connects...you are looking at the core and the holes for the tubes...do you see solder bloom or what looks like white fluffy doughnuts around the holes....

Its common at this age and you will need a citric acid flush to reduce that...

However any tubes that are blocked will remain blocked...do you know anyone with a non-contact infared thermometer? on a hot car take temps at various points on the core to see if there are obvious cold spots that point to blocked core.

bruiser · #7 11-10-2005, 10:20 PM

drove the car for like three hours today, both high speed and town. good thing i bypassed the servo to get heat, because it seems like the gauge just slowly creeps up until i turn it on, then drops even further than normal, down to 175 before i'd turn the heat off and let it warm up again. so essentially i'm ping-ponging between 175 and 212 by turning the heat on and off every 5-10 minutes, i don't know how extreme it is willing to go either direction, don't really want to find out.

other than the temp, the car is running normally, though the intermittent squealing from the front was really out today. it had only been squealing before when it was wet out, and since a water pump is much cheaper than a radiator and less time consuming than an acid flush, i'm going to have to try that first to see if that will stabilize temps. i was under the impression that if a water pump failed, you would necessarily overheat because the coolant would quit circulating, but is there any chance the little pump next to the servo is circulating just enough to not overheat (aided by the heat dissipated by the heater), and that is why my radiator fins are cool to the touch through the entire body (though hot at top and slightly warm at the bottom), because the coolant has so much time to cool in there? can water pumps fail and the car still driveable using the aforementioned technique?

i got a new rad cap at the dealer today, but it didn't do anything different for me (even though i had a 100 and it's a 120). not going to pay dealer price for a water pump, so i'll just keep ping-ponging for a few days until it's delivered. i guess if the water pump and testing the replaced thermostat doesn't do anything, i'm kinda down to the radiator.

#8 11-10-2005, 10:42 PM

If turning on your heater causes the car to cool down that indicates that, your water pump is good. The link is to a outstanding artical on how to trouble shoot your overheating problem when your on the road and have little more than your wit it is written not by an automotive specilist but by a proffesional trouble shooter I hope you find it as helpfull as I did with my W116 over heat problem.
Dave
http://www.troubleshooters.com/tpromag/200210/200210.htm

t walgamuth · #9 11-10-2005, 11:16 PM

i wouldnt say that the heater helping necessarily means the wp is ok. if any element of the system is malfuncioning and it is getting hot increasing the size of the radiator (which is basically what you do by turning on the heater) will always help.

the wp can fail slowly or all at once. no set pattern. i have had them fail many different ways through the years. on a benz they usually fail by leaking. but i would say not always.

the t stat should be installed with the disc down.

and the fins on the rad can be plugged on the outside. also i suppose your condenser could be plugged too and block the air fl0ow that way.

good luck

tom w

#10 11-10-2005, 11:54 PM

.The size of your radiator is not significantly increased if there is no water being circulated. If you hooked your heater hose to the hover dam there would not be enough thermal heat transfer to cool the engine with out the water circulating via the water pump. While it is rare for the impeller to break or rust away to the point of little or no water circulation it does happen. The heater trick tells you that indeed water is circulating.

Water pumps that fail by dripping water out of what I call the weep hole are actually failing properly by warning you the bearing is about to fail. I ignored this drip on my first car after months of just adding a bit of water in the morning the bearing failed sending the fan through the radiator. The aux water pump may make this test useless on a Benz though. Plugged radiator fins are a real possibility. I spent 10 minutes blowing compressed air through the rear of the radiator yesterday on my 76 240D before giving up and pulling the radiator there was so much crap in it a proper out of car cleaning was needed.
There is nothing I hated more than racing through the desert with the blasted heater on full blast to keep the car cool and us cooked.
My 2 cents and no budget auto lessons I could always be wrong
Dave S

bruiser · #11 11-10-2005, 11:57 PM

i would think that the fins being plugged would cause a gradually escalating problem over time, whereas in my case it was a sudden overheating with no previous symptoms. i'll probably run compressed air thru the back of the fins tomorrow and see what comes out, but can't i just test radiator flow by hosing water in the top inlet and seeing how long it takes to clear thru the bottom? if it's clogged enough to cause my problem, i figure it would take a while.

the thing is, if it was the water pump, i don't think i'd be able to crank the heat full blast for a half hour (my face is chapped), since the coolant wouldn't be moving thru the core fast enough to provide that heat. but then again, there's the occasional squealing, maybe i'll tighten the belts and dress them and see if it keeps doing it.

thanks for the help guys, i'll keep at it. just nobody mention head gasket yet, please.

#12 11-11-2005, 12:16 AM

Any decent radiator shop should be willing to test your radiator with one of those tempature guns but you can do the same thing with your hand feeling for cold spots on the radiator with the engine hot but not running.
Dave S

#13 11-11-2005, 02:01 AM

I got my W116 radiator rebuilt locally for $95. My dealer quoted me $840 for a new one.

t walgamuth · #14 11-11-2005, 09:11 AM

it is possible for the water pump to be pumping but not up to full capacity. in this scenario operating the heater could help.

and dont forget the aux water pump.

tom w

Mr.Kenny · #15 11-11-2005, 10:28 AM

I'm going to throw out my 2-cents worth in the wierd but true department.
My friend had a honda that started overheating only at highway speed...sometimes, not always. After replacing t-stat, radiator; next was the water pump, a big job in a honda (while on vacation I might add).
While inspecting the water pump,.....just on a whim he held the pulley on one side and turned the impeller on the other side. Whaaa?? The impeller was not tight on the shaft, but tight enough to work at low rpms but not at higher rpms. Ahh! Problem solved.......sort of. He goes to the auto parts store inspects the newly rebuilt mexican water pump. The impeller is on backwards!??... on a whim he holds the pulley and turns the impeller. It spins on the shaft right out of the box!
Parts guy says "well look at that".... The next pump was o.k......& problem solved.