i just bought a 77 450 sel that i really enjoy. i had driven it on several 30 mile trips w/o issue, but while driving 100 mi from anaheim-palm springs, the 250 degree temperature gauge (which had been reading 175-190) went up to nearly 240. i saw no steam or power drop-off during the trip or afterward, and the car made it home w/o any problem.
looking over the previous owner's meticulous records (a one owner 124,000 mile car w/ ALL service records demonstrating he never missed a service interval), i note that he had replaced the water pump and thermostat less than two years and 1500 miles ago. He replaced the coolant expansion tank about 3000 miles ago.
my question is, what's my problem? what temperature thermostat should this car have? Looking online, i saw units that opened between 160 and 196 degrees. have these cars had issues with high engine temperatures, or w/ the gauges reading artificially high? has anyone else had a similar problem, and if so, what was the cause? it seems weird to replace a thermostat or water pump after so few miles. could my radiator need a recore or some other kind of service? something else?
any advice would be greatly appreciated. i don't like to take cars to mechanics before getting at least SOME idea what is wrong.
one more question: so far i've gotten about 15 mpg. does that seem about right for this model?



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Living in California and driving few older cars, I had to replace radiators on several of them.
Over the years the build-up inside lowers the efficiency.
Check if the Kragen is having one for your model. They offer good prices and lifetime guarantee.

 

kajtek1,
thanks for the tip. i'll check w/ kragen for price/availability. would what i'm describing be indicative of a new radiator? flush or recore inadequate, or bad cooling fan?
I looked over the owner records, and there is no indication that he replaced or worked on the radiator.

 

From what I remember the freeway to Palm Springs is having nice grade and good winds. They didn't put those windmills there for nothing.
So your car worked much harder, than usual. Raising temperature was indicator, that radiator couldn't keep up with the demand.
Sounds like this is not bad yet, but it might fail, when you need it the most. Good test is to let it idle on warm day for about 20-30 minutes, observing the fan draft.
You could do the full testing with infra-red thermometer, but if the radiator is 29 years old, I wouldn't waste my time.

 

kajtek1,
thanks for your help. i really appreciate it. Yeah, the area where i noticed the problem had a fairly steep uphill as well as wind.
i was looking back at previous posts under 'temperature.' i actually came across your handle in a couple articles. one post had a service memo stating that under stressful conditions, the temp could go pretty high and still be okay. Is that par for the course for mercedes? i'm just now used to seeing a gauge reading at 225 plus. Are they measuring temp at a different place than other car makers?
i agree that i probabely ought to just replace the radiator. but i would also like to go ahead and buy the thermometer unit you mentioned so i can have one in my tool box. it sounds like a gizmo that could come in handy!
i'll do your 1/2 hour idle test, do a thermometer test (after i get one), and probabely STILL replace the radiator! an ounce of prevention ...

 

I find that a good test is to drive the car at about 40MPH, then pull up sudendly, switch off the motor straight away and then, as quickly as possible feel the radiator for hot and cold patches. It should have a fairly even temperature across it. If there a cold patches, then you have blockages in the core.

 

dondas,
thanks for the tip. i'll try it out tomorow morning. i did some of the earlier stuff suggested by kajtek. i did a pressure check (it held pressure even though in my ignorance i put a LOT more pressure than i think i was supposed to). i also let the car run for a half hour plus. it never got hot, but the small fan in front of the radiator immediately behind the grill never started (if its even supposed to). i'm going to have the radiator professionally flushed and do a diagnostic. on the way to that i'll do your 40 mph test.
mike

 

Those models have strange set-up where electric fan on the radiator is activated by AC, so not having it running might be normal.
Never met anybody, that was happy with radiator flash. Those chemicals don't work too well on the boiling stone and unless you have plain dirt in the radiator, you won't see much difference.
There is procedure for taking radiator apart and brushing inside the coils, but don't think they can do that on plastic sides and with high labor cost in CA that might cost more, than the new radiator.
Sounds like your radiator isn't too bad, so you might still use it. As long as there is a coolant )even boiling) in the system, there is no danger of the engine damage, so I wouldn't panic with temperature raising.
The infra-red thermometers were on sale at Radio Shack for $29. It is amazing tool. You can make a quick tire check on the road and high temperature might indicate low pressure, you can spot weak cylinder in the engine, you can find clogged (cold) spots on the radiator and test if thermostat fully opens and at what temperature.
Supposable you can test your wife, or girlfriend for some temperature variations, what indicate her biological status, but I never went there.

 

kajtek1,
hopefully i have ended whatever cooling issue saga i was having. i took my car in for a cooling system check and a radiator flush, but the mechanic was honest enough to tell me that he wouldn't be able to test for a problem that only occurred during high load, and that a flush wouldn't do anything for a blockage 99% of the time. he said that since i was only cooling during high load, it had to be a blockage in the radiator (like you said it was in the first place - thanks for your knowledge!). he said if it were a fan clutch, i would be overheating all the time, which i wasn't. he said i should get a recore, and suggested a place where he'd had work done. you CAN get good advice at pep boys!

i checked around, but couldn't find a radiator for my car for less than $500 bucks. so i did a recore of my old one. they gave me an exrta row of coring, and it was $330 out the door. the car ran at least 10 degrees cooler than what i had thought was the normal operating temperature. i felt pretty good about the car's temp under normal conditions, but didn't want to fool around and risk catastrophe. better to take a little pain now than a lot of pain later, right?

 

I know the feeling. Last spring I spend $1200 for re-coring my motorhome radiator.
The new one was $3600.
Still well worth it, than being scared each time you are on the grade and take a look at the temperature gauge.
Now, for the real test of cooling system you can go on the Strip in Las Vegas.