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Hello all,

General question on operating temperature on a 79 450 SEL.

When I first purchased the car the temp gauge would intermittantly go above the 220 mark. It turned out the thermostat was defective. Now it usally stays around the 175 mark. Sometimes on warmer days it gauges in between the 175 and 220 mark.

So my question is what is the normal operating temp on these cars. Is it normal to go as high as 220?

In southern California we get up there in temp.
 

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1979 450SEL
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My 1979 450SEL usually operates just above 175 and "212ish" as I guess it might be. I just know its that mark lying in between 175 and 250 on the gauge cluster. [;)]
Anything between 175 and 212 seems pretty normal to me and I haven't had any problems with my car overheating at those temperatures. [:)] Anything above 212 though...well might be a bad thing. [:O]
 

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1989 W201.029/M103 3.0
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A petrol engine, any engine runs best and lasts longest at around 180. Orientate your radiator, thermostat and underbonnet temperatures to keep it around 180 in your driving environment.

Some subtle louvres towards the rear of the bonnet will help. Heat coating the exhaust manifold (tape can be bought for this pretty inexpensively, but aluminium powder coating is best). An electric thermofan to keep temp variations less dramatic (also reduces crank drag).
Oil temperatures also contribute to variations in running temperatures. Primarily poor circulation effects due to crankcase windage (also a huge horsepower drag). So a custom fitted windage tray/crank scraper in your sump is always a top boon and doesn't cost much. Hell, get a whole new one custom made, I would, damn thing's are just tin and it's all too easy.
 

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1989 W201.029/M103 3.0
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Aluminium heats and cools quickly and so is prone to variations in running temperatures but that's not such a good thing. Part of the longevity in cast iron small blocks is the fact they take a long while to heat up, but temperature variations and heat expansion/contraction are much less extreme.
So it's a trade off. Aluminium burns fuel better and is lighter, but then cast iron doesn't go around cracking all over the place when you burst a hose one day, or run it a bit warm for a while and then switch it off...

So yeah, it's smart to take notice of extreme variations in your running temperature, but it's not an uncommon thing. Still a problem but, the inherent weakness of aluminium engines.
 

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The main thing to watch,and this is Mercedes own reccomendation,is that in heavy traffic the guage will reach the top of the scale around 200*F .BUT,IT SHOULD DROP as soon as the car moves fast enough to have cooling air through the radiator,I find this happens immediatly.If it stays in the upper end of the scale all the time you have a problem.Start by going to a radiator shop.You have to get a "breath alyser " check to ensure that no head gaskets are leaking,then get the whole system reverse flushed.replace the coolant with the correct mercedes stuff.Don't waste money by pouring in generic antifreeze.
while you are getting the system flushed,ask the rad shop to check the fan belts.if they are looose- the pump will not be working .
The cap should be tested to ensure it's not leaking.These cars run at a high pressure,if the pressure is leaking,you will get a hot running condition.For every pound of pressure ,you get a drop in temperature.
The correct Mercedes cap is the ONLY ONE to use.
It's marked with a "100".
Finally,get the rad shop to do a pressure test to ensure there are no pressure leaks.
Thermostats sticking are sometimes a problem,but it's rare.
If none of the above is successful,get the igniton timing checked to ensure it's on the button.Ensure the trans is not slipping,the cooler is in the bottom of the rad. and it will heat the water very quickly.
 
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