Cooling: Slow overheating

[PanzerSD]

My 78 450 SEL's overheating problem is rearing it's ugly head again, as the temps here go up.

On a moderate day, with ambient temps around 20*C the coolant temp hovers around 80-85*C On sunnier days, with temps around 25*C it gets up to 95-100*C With the car moving the airflow barely cools it down, and if I'm st a slow light, the temp climbs..but doesn't ever seem to get to the top. It (so far) hasn't ventured above 100*C.
Could my radiator need replacing/re-core? or can I bet on it being a fan clutch? it moves freely (with engine off) whether it's cold or hot.

[wolf_walker]

Originally Posted by PanzerSD

With the car moving the airflow barely cools it down,

That usually says something other than fan clutch. It's usually best to service cooling systems all in a go, replace the thermostat, verify or preferably replace the water pump, flush the radiator or have it boiled or chemically cleaned by a shop better yet, and flush the rest of the system yourself. This time of year does this sort of thing to old cars. My 280 will get warm sitting at a light too, but cools right off, weak fan clutch. The electric fan will kick on eventually if it get's really hot, but I've only let it do that twice to see if it would. Don't ya love old cars?

[PanzerSD]

Originally Posted by wolf_walker

This time of year does this sort of thing to old cars. My 280 will get warm sitting at a light too, but cools right off, weak fan clutch. The electric fan will kick on eventually if it get's really hot, but I've only let it do that twice to see if it would. Don't ya love old cars?

Actually, Yes, I do love these old cars...

[wolf_walker]

Originally Posted by PanzerSD

Actually, Yes, I do love these old cars...

Yeah me to, but I've found it advantageous to keep two or four of them around at the same time. Better odds of having one working when you need it.

[PanzerSD]

yeah, I have nither the money nor the space for that thou, the best I can do is have an engine in my parent's garage that I am 'freshening' for an eventual, but hopefully unnecessary transplant. and I have my SD for some parts. but not a lot.

[PanzerSD]

Question! is it possible for one valve plate in the thermostat to fail but not the other?

[wolf_walker]

valve plate? got me on that one.


it's harder when young but the more cars thing gets easier. If I was single I'd have old car(s) and a motorcycle. I was thinking bout your overheating as I was taking the 280 back to the farm to pick up my rabbit to drive tomorrow since it's likely to be upwards of 97F, as the temp gauge crept up and I smelled coolant a mile out. One of the handful of random coolant hoses popped, made it home without a tow, left a mile long trail on the road though.

[PanzerSD]

Originally Posted by wolf_walker

valve plate? got me on that one.


it's harder when young but the more cars thing gets easier. If I was single I'd have old car(s) and a motorcycle. I was thinking bout your overheating as I was taking the 280 back to the farm to pick up my rabbit to drive tomorrow since it's likely to be upwards of 97F, as the temp gauge crept up and I smelled coolant a mile out. One of the handful of random coolant hoses popped, made it home without a tow, left a mile long trail on the road though.

Valve plates, the two thermostat bypass plates that block passages as the coolant warms up. When the coolant is closed, it blocks passage to the radiator for cooling. At the same time it stops coolant from radiator from entering the engine, effectivly isolating the engine from the radiator untill higher temps...or as I understand it at least. Makes for faster warm-ups??
Anyway, I'm ordering a new thermostat tomorrow, We'll see what that does, if nothing, we move on to the next replaceable part.

Sorry if I influenced your house failure

[PanzerSD]

And I imagine that when I get to owning my own house I'll inexplicably start collecting Mercedes "It followed me home honey!" lol I need a commuter (190E) a traveller (300D) and a toy (SEL) odd that I start with the toy

[mercmad6.3]

It sounds like the fan clutch isn't working. It's fairly simple to diagnose ,with engine dead cold,start the engine with the hood open. the fan should make a roaring noise which dies off as the oil in the clutch becomes more viscous and the fan slows down. When the car gets to normal temp (80-85 C) shut it off while watching the fan. Does it stop instantly ? or does it keep revolving? if it keeps revolving it is definitely worn out.
They are reasonably cheap and easily replaced.
A stuck thermo will either make the car run too cold or run too hot if stuck closed but a worn thermostat is quite rare in fact.

[Emmerich]

If you overheat at slow speed but not high speed, you are not getting enough enough heat transfer through the radiator. Thermostats are a HUGE restriction in the system, and if the car is old the radiator could use a flush and cleaning. My 6.9 temp varied a lot compared to all other cars I had, same with my 6.3, the needle moves a lot based on car speed and with the 6.3, if the a/c is on.

You might have corrosion in the engine water jacket, an acid flush would help with that. Sometimes you need to keep doing it until the water comes out clean. Also, if you have air in the system, that is a killer.

Getting the radiator cleaned is not a big deal it is easy to remove the radiator and take it to a shop for that. I have a couple of .pdf files that I created when I removed the 6.9 and 6.3 radiators. The 6.9 is a 116 car and would be very similar to yours. Let me know and I can send them to you.

[compu_85]

I would also double check that there isn't a bunch of crap between the ac condenser and the radiator.

My SDL's temp gage would creep up and up and up when I was on the highway and had the AC on when the fan clutch was dead.

-Jason

[PanzerSD]

OK, I know there isn't anything in between the radiator.
The air conditioning is inoperative.
the fan moves with little effort and feels cushioned, as opposed to some sort of rubbing/grinding feeling..hot or cold. However, it stops turning when the engine stops turning.
I have yet to do a flush, the heater servo and aux pump is bypassed with a ball valve I put in to shut the heat off to the heater core in this heat.

The system pressurizes normally, the cap tested good, no external leaks or bleeds.

In the winter warm up's are fast and it doesn't overheat. stays at around 80 or less if really cold.

I don't have the gauge readout to vehicle speed relation though. it starts cold, and if it's cooler out it'll stay 80-85 IF i can stay moving, in a drive-thru it will creep up.

It still has yet to pop the cap or go over 100. I also noticed that the idle gets rough when it's hotter than 85. a chance my timing could be too far advanced somehow??

[PanzerSD]

There is however, an inline block heater in the lower hose.....

I'll bet that the element in the heater has collected some crap and is causing a partial blockage! It has to be a blockage somewhere...Frustration..

Oooh! almost 2,000 post's!

[Tomguy]

I'd second the accumulated crud in engine theory. I used, not knowing better, that red crap they put in GMs (don't know if they still do) that's supposed to last 100k. When I did my cylinder heads, the water jackets and cylinder walls were covered in red goup. When I cleaned it out (no pressure washer so I used a garden sprayer & shop vac w/1/2" hose to clear out the water/debris mix), my engine temp almost never rose above 175°F. Also have to thank CTH for that rad I bought off him a while back for that, it was boiled out and super-efficient. Stock, these cars run cool (much cooler than modern ones) at 175°F and arent meant to venture too far north of that unless AC is on and it's super hot out, then it might (MIGHT) get to 212° in heavy traffic on a 95°+ day w/AC on.

Easy thing to do: When you replace your thermostat, drain your coolant, use a garden hose to reverse-flush the radiator (water in the bottom, out the top), flush & reverse-flush the block, stick a hose as far into the block as you can & suck out remaining water, and then do a citric acid flush w/o t-stat in, and re-flush everything with water. You may get away with not needing a new or re-cored radiator. The thermostat handles the water flow to and from the rad and block, so there are no other valves in the system that would fool with your coolant flow. It does sound like your fan clutch may be bad as well, and replacement ones can be expensive; you may want to rig your electric fan to run via a manual switch to test this theory.