id bet the farm AND the Ranch

[mbcoupe]

hello wasssuP and just plain howdy to everybody.. my name is Tom and im a Mercedes Mechanic who worked at the dealership for a few years and i just bought a 96 reg cab bone stock XLT 4wd 5spd.. im 54 , master certified by MB,i hold and F.A.A. Powerplant lLicense and even got an FCC tech class license way back in the early 90's when they were paying people to take classes and take the exam..lol..well it seemed like it anyway..anyway this truck of mine is kinda being a pain in the butt at times cuz its been running HOT.. especially with the A\C on..it also had a bad case of rust in the cooling sys...ive seen some interesting suggestions on how to remove the rust..anyway.. i figured the radiator was probably clogged even tho it was HOT ALL OVER THE CORE..but i went and found a near new radiator out of a ranger with 4.0.. its alot bigger.. but it didnt help the problem at all.. even with tstat removed it would boil over while idling or any RPM below 3000...so in other words if i drive it hard i the temp comes down FAST...tstat in or out.. no difference..so ya know it took me a few days to come up with this theory...and ive only seen it one other time in 35 years of fixing cars,boats, aircraft,helicoptors,.. why would an engine only cool at max rpm..loaded or not

 

[Mark_88]

Howdy...welcome to TRS...

Well, you will probably get enough good advice on here to fix the problem soon enough...but it sounds like your fan is not working properly...

Being as this is the introduction forum you may or may not get a whole lot of advice though...so I'd say if you don't then try posting in the appropriate engine forum below or the Need Urgent Help section since you've already tried to fix the problem on your own...the Urgent section is more for people who are stuck in the middle of a repair or upgrade but it's also where a few of the gurus hang...

Anyway, you're on TRS now so hopefully that will be resolved quickly...overheating is not a good thing as you well understand...even more critical if you were driving a 4 banger but the 4.0 is just as susceptible to heat damage...

 

[snoranger]

I ran into a cooling problem at low/mid RPM range once before that turned out to be a bad water pump. The impeller blades were damaged/ missing and it would only flow enough coolant when you kept the revs up.

 

[88_Eddie]

I ran into a cooling problem at low/mid RPM range once before that turned out to be a bad water pump. The impeller blades were damaged/ missing and it would only flow enough coolant when you kept the revs up.

this is exactly what i was thinking.

 

[Tominator]

Anytime you have a cooling problem and there are no obvious defects, the first test is if the cooling system isn't losing pressure.

At speed you may be getting enough airflow to keep the temp down below boiling. But at idle or low cruise the fan is not enough.

If the radiator gets hot all over that rule's out the WP being bad IMHO. Infrared thermometers are cheap and VERY useful in verifying problems involving heat.

Things to check...lower radiator hose not collapsing. Weep hole on the WP dry.
Fan clutch or electric fan working properly. NEW radiator cap....looks don't crap. Overflow bottle no cracks or clogged hose.

Do the pressure test next.

 

[triumphrider-1]

I ran into a cooling problem at low/mid RPM range once before that turned out to be a bad water pump. The impeller blades were damaged/ missing and it would only flow enough coolant when you kept the revs up.

I agree. My truck did the same thing. I started with just a coolant flush (also used the prestone flush/cleaner stuff), which helped; but I didn't get mine back to normal until I changed out the water pump.

Also, as Tominator mentioned, check that the fan is operating properly.