Running hot, can I flush for a week or two?

[Robert W. Roe]

My SD has begun to run over 100 deg C a couple times on the highway, reaching 115 or so for a minute or so. I suspect I am due for a flush and new coolant. I'm also hearing a squealing sound, making me suspect perhaps a water pump bearing or something. The belts look good, and there is no noticable leakage at idle. I did notice that the coolant appeared to be "flowing" (I hesitate to say bubbling, because I didn't see any bubbles, just some movement) inside the overflow tank where the hose from the radiator enters the tank.

I'm wondering if I would help matters by getting some citric acid and putting it into the overflow tank and letting it clean out the cooling system for a week or two until my tech can look at it.

Would leaving the flushing solution in for this long cause corrosion? Just wondering. Any thoughts appreciated. Thanks,

[Robert W. Roe]

Thanks for the reply, Bill. It sounds more like a belt shrieking / squealing rather than a grinding. I just looked at the belts while it was running, and didn't hear anything. I didn't really check them with the engine off. It has been fairly humid, though not really warm; it's been around 70 degrees F.

I notice the temp pushing 115 maybe for a minute or two, then it'll drop back to 100-105 gradually. I have observed the needle drop by 10 degrees within a split second, leading me to suspect the electrical portion of the sensor's readings.

How fast would the thermostat opening make the guage drop? It happens so fast that I suspect and electrical intermittent/corroded contact. Sometimes when she's running at 100 deg the guage will drop back, very suddenly, down to 90.

I do hear the aux fan running, and it doesn't seem to be running in the wrong direction. I also see the main fan running but don't know how to check the fan clutch.

Thanks again for the reply...

[Robert W. Roe]

Bill, thanks for the replies. Driving today I kept a closer-than-usual eye on the gauge and it only jumped once, up and down maybe 2 or 3 mm. I always suspected an intermittent electrical connection, but I suppose it could be a mechanical aberration withing the gauge also.

I did have the thermostat changed about a year ago, when the car wouldn't warm up above 60 deg C except after 8 miles or so. I suspect MB thermostats are fairly variable in quality. I may just get my tech to change it along with new coolant, flush, and all new belts the next time it goes into the shop. I've been saving up my $$$ for a new steering box, and I'll have them also check the rear end for some vagueness.

thanks again Bill!