Seal damage on radiator cap / fluctuating temperature - is this the problem? - also.. - PeachParts Mercedes-Benz Forum

86560SEL · #1 01-23-2006, 09:51 PM

When on the highway, my car runs cool. Well below 80*C, but when in town in stop-go driving it will go to about 90*C, if the temperature outside is over 65*, but never goes over 90*C. I noticed the other day that my radiator cap seal has a tear in it.

One day when in town, I made a quick run in the supermarket and when I came back out, I saw anti-freeze coming out of the top of the reservoir - where the hose comes out, but it has a puncture. I was once told that if my cap seal was damaged that this would happen. Is this true? It has not leaked since then. Could this be why my gage fluctuates so? Perhaps a faulty thermostat? I think I will at least change the cap and see if this makes a change. I have to change out my green coolant anyway.

Thanks.

BTW - also an oil question. As my car (and others) warm up, oil pressure typically lessens. I would like for my pressure to be higher when the engine is hot. Whats better for the best pressure when it is hot? 20W-50?

Thanks!

t walgamuth · #2 01-23-2006, 11:18 PM

yes a leak in the pressure system even if above the water line will cause warm temps. is that enough to cause your problem? no way to know. but fix the leak and see if the problem is solved.

on the oil pressure, it will always be less when the motor warms up. the parts expand and make more room for the oil to circulate hence the pressure drops.

if you have good oil it will usually peg it at ldle when cold. after it warms up it will drop. a good engine will have 1.5 bars. minimum is .5 at warm idle on a warm engine, i believe.

tom w

86560SEL · #3 01-24-2006, 12:23 AM

Thanks Tom,

I really do not (or at least hope not) there is a problem, because I have heard that 90*C is not uncommon and it normally stays around 80*C, but it is the wide fluctuation I was wondering about. I will try a new cap. Should I go to the dealer for a new cap, or will one from an auto parts store be sufficient?

About the oil - we have talked about this in detail in the past. My car does peg at idle when cold and when fully warm (80*C), it idles at about "1", when it is slightly below 80*C, it is about "1.5". When fully warm and in gear, (500 RPM) it is around ".3". In the owners manual, it says this is correct, but there were times when it was around 90*C that when I would come to a stop, it would drop to ".1", then back to ".3" which I do not like. My car does have 264K miles and it is 21 years old, so I do not expect the engine to be up to new standards.

Perhaps it is normal, but I am not used to these cars yet and a bit paranoid I suppose. I used 15W-40 oil last time and was wondering if any other weight of oil would increase it. Guess not.

Thanks!

sbourg · #4 01-24-2006, 02:35 AM

Can't help with the oil, but if the radiator cap is removed after the engine has been off for awhile (but not overnight) and there is no release of pressure, the cap is bad or there is a loss of pressure elsewhere. If you lose pressure while running, the coolant can locally boil and then will cool and circulate ineffectively. If you suspect the cap at all, do a system pressure check and replace the cap before trying to judge cooling performance.

Steve

G-Benz · #5 01-24-2006, 12:07 PM

Not sure how long you've been plagued with temp problems, but make sure the cap is screwed on properly. There are notches along the bottom of the cap and around the reservoir spout...I have at least once, put the cap back on and not screwed it tightly beyond the first set of notches. The result was higher than expected temps and boiling over after driving.

Go ahead and replace the cap first...cheap insurance.

sjcruiser · #6 01-24-2006, 12:32 PM

I had the same problem. New thermostat and two the expansion tank caps later, the operating temperature is much more consistent.

I bought the 1.2 bar cap first but it did not seem to work well - thus switching to 1.4 bar one (superceded replacement part)

Frank.

Hatterasguy · #7 01-24-2006, 12:32 PM

Replace the cap and flush the fluid.

I have the perfect oil for you! Castrol High mileage 20w-50. I am pretty sure I just saw this stuff at Autozone. I used the 10w30 in my Toyota for a few years and it works as advertised it softens old seals and makes them seal better.

Also this time around use a better quality filter it will probably bump your oil pressure up a bit. Head for the dealer and spring for an OE filter.

t walgamuth · #8 01-24-2006, 10:45 PM

you said the pressure drops when you stop. is your oil level correct. the oil pressure dropping to a very low reading and coming right back up could be from the oil rushing away from the pickup if it is low. and if you are stopping very hard.

tom w

86560SEL · #9 01-25-2006, 12:10 AM

Yeah - I checked it and it is full. The PO had let the oil go well beyond the time to change.

The filter was so old it had a big hole in it that was not supposed to be there.

I put on a cheap filter- which may be the problem. Perhaps like Hattaras said, if I use a genuine MB filter it will improve? Maybe I should also go with the high mileage 20W-50 oil on the next change....

Thanks again.

t walgamuth · #10 01-25-2006, 12:55 AM

about the filter affecting oil pr. i dont understand how unless it actually presented too much resistance to flow.

the heavier oil is a good idea. it should bring it up a little. i would also prob avoid the synthetic in this case since it tends to be thinner.

tom w