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  #1  
Old 09-23-2001, 09:34 PM
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Question normal operating temps for a 1975 450SL?

Hello

Would like to know at what temp does your 1975 or close to that year model 450SL run at normally?

My concern is that mine runs normally at around 175, I realize that the catalytic converters in the engine compartment don't help things in terms of temperatures but need to know if others with same engine are seeing same temps as well.

I believe the high heat is whats causing the vapor locking symptoms mentioned elsewhere in the forum. Symptoms such as hard starts when engine is warm but not when cold.

thanks in advance

dom
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Old 09-23-2001, 10:15 PM
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Most 450s run 2/3 the way between 175 and 212.

Usually D-jet cars that are vapor locking are running too lean to begin with. Sometimes setting the fuel pressure a few pounds higher helps. VW had enough problems with vapor locking that they installed a blower that blew air across the outside of the injectors.

To be sure that vapor locking is the problem you can try jumping the fuel pump for about 20 seconds before you start. This will cool the fuel rail using the fuel as a coolant.
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  #3  
Old 09-23-2001, 10:49 PM
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thanks for the info, am much relieved that 175 is within normal range for a 75. What exactly do you mean by "jumping the fuel pump" though? Do you mean switching the ignition off and on, waiting for the fuel pump noise each time, several times?

thanks again
dom




Quote:
Originally posted by stevebfl
Most 450s run 2/3 the way between 175 and 212.

Usually D-jet cars that are vapor locking are running too lean to begin with. Sometimes setting the fuel pressure a few pounds higher helps. VW had enough problems with vapor locking that they installed a blower that blew air across the outside of the injectors.

To be sure that vapor locking is the problem you can try jumping the fuel pump for about 20 seconds before you start. This will cool the fuel rail using the fuel as a coolant.
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Old 09-23-2001, 11:09 PM
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Actually, I had intended exploratory surgery. Doing the off/on thing a number of times would accomplish the same thing. It would take 20 cycles to run the pump the same length of time.

The key cycling will work though.
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  #5  
Old 10-06-2001, 08:31 PM
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followup

hello

just wanted to do a followup on this thread:

1. topped off the expansion tank for the radiator with 50/50 mix of MB antifreeze and water to required levels.
2. put in a bottle of "water wetter".

she now runs consistenly at just above 175 on the temp gauge and has not crept up past the 200 mark or even close so far.

I plan to take her out on the expressway tomorrow to run her up to 80 at least to see how she does.

I think I am stuck with my having to hold the accelerator down for two seconds prior to cranking a warm engine. She starts right up with that method and consistently as well.

Someday I will get a fuel pressure check done...she's almost due for her 87500 mile check so I'll ask the MB mechanics to check that out as well.
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Old 10-09-2001, 09:48 PM
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got fuel pressure leak check done

the car passed with a steady pressure of 35psi so not sure if fuel vaporisation due to heat in the engine compartment can still be seen as the culprit for the warm engine hard starts issue.

on a different note, took her out on the highway yesterday, got up to about 90 for a few minutes....once I got off the highway she would idle roughly when stopped at lights, and I noticed she was idling at around 400-500 vice the normal of 700-800 when in Drive.

she appears to do this when the engine is closer to 200 than the normal 175.

once she cools down, she idles just fine with only very minor intermittent shaking that is almost inperceptible...go figure.

just updating this thread, am almost to the point of writing this off as quirks of an old car.

only one thing left to replace, the spark plug wire set which is in the mails I am told.
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Old 10-12-2001, 08:40 PM
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more followup

I replaced the spark plug wire set and adjusted the idle adjustment screw to rev a little higher than it was set to...maybe a quarter turn at most.

She now idles in neutral at just above 1000 and at just below 1000 when in Drive. Idles very smoothly now while doing city driving, have taken her up to 80 on the highways on the way to work and she idles just fine afterwards without the previously mentioned fluctuations.

Am a much happier camper now, I know it should be set to idle at between 700-800 rpm when in neutral according to the data plate on the chassis but it works better with this setting so am sticking to it.

Someday I'll try and figure out the real reason why she won't idle smoothly at the manufacturer recommend settings, who knows, perhaps a 26 yr old car wants a little more rpms than when she was brand new.

dom
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