Newbie questions about engine temp
 

Hello everyone! I am the very proud owner of a 1977 450SEL with the 4.5L V8. The car is in great shape (three identified areas of small rust) and has been undercoated at one time. Car currently has just shy of 40,000 miles. My question is this.

Concerning engine coolant temp. When I first start the car the needle is buried (pointing right at 6 o'clock position) and as I drive is slowly comes up, so I feel it is working. However, it only gets up to between 175 and the tick mark immediately below 175 (150F???). I don't think that is warm enough. The vents will blow hot air so the heater core is getting coolant. My concern is that I live in NJ, need to get the car inspected and am worried about emissions. Also, winters here are cold and I need the heater to work when it is real cold out.

Ideas? Thermostat stuck open?

Welcome tomfowler!

Very low miles! What color? Sounds like a great find.

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Once warm and running-

I would suggest the basics first ... find the coolant temperature sending unit and take the wire off the sensor and reconnect it to make sure you are getting an accurate reading.

If you can, find a way to measure the real coolant temperature.

Check the radiator .... engine off .... for even warmth all over it.

It certainly could be a t-stat stuck open. Removing it and testing it on a kitchen stove is a quick way to know.

Keep us posted,

Haasman

I'm 99.4% sure my 78 450SEL had a mechanical temp gauge (with capillary tube?) so I imagine there's no connection to clean on a 77. Maybe I'm confusing it with the mechanical oil pressure gauge.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD
78 450SEL (sold)

So am I correct in thinking it is too cold?

It is Mercedes grey. Course, that's one of the things that needs some attention. It is quite faded.

Any sources for a repair manual/CD. I checked Alldata and they only go back to '82 I think. eBay didn't have anything. I've heard the Haynes manuals are good. Do you still have the manual for the 78 450SEL you sold??? :)

175F is 79C. Most MB thermostats are 80F or higher implying that the operating temperature should be 80-85F. So lower than 175F would be too cool.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Congrats on the find -- low miles!! I'm envious!!

The dash temp gauge is not a finely calibrated instrument. Use it only as an approximation for the engine coolant temperature. Don't rely on it for absolute temperatures. It is more useful to show trends, such as when the engine warms up, what the steady state temperature is, and when it's beginning to overheat.

I agree with haasman. The only good way to check out the thermostat is to remove it from the car and test it on the kitchen stove it in a pot of water.

Buy the Haynes manual until you can find a better one. The money you spend on these things will pay for themselves many times over.