Mercedes 450 Cooling (Page 1/1)
rogergarrison OCT 15, 01:00 PM
Im sort of stumped and looking for some other ideas. My 76 450SL was running hotter than I consider normal. It had a 175* stat. It goes up to 230* in traffic. I replaced it with a 160* stat (that manual specifies). No change. I replaced the radiator with a New OEM. No change. The timing is on spec and engine runs like a watch. Hoses are all new. I replaced the fan and the fan clutch. No change. I cut out the middle of the stat so its open all the time. No change in traffic, but is below 175* on highway. Replaced OEM electric fan and switch (it comes on at 220* and shuts off when its supposed to). It has 50/50 antifreeze mix. There is no air pocket, its been drained and refilled 5 times, some with pressure filling. I removed the air conditioning condenser so radiator is directly in open air & removed the compressor belt. The water pump is circulating fine as upper and lower hoses/ radiator reach same temps as does the overflow tank. Heater & defroster work fine. There are no combustion leaks into water system, and no water in the oil. Radiator cap is spec and system does hold proper pressure. The water pump and alternator spin easily with no drag. Im sort of outta ideas. Normally the car should not go over 175* in traffic with AC on and idling for an hour or more. I dont use AC.
jaskispyder OCT 15, 03:18 PM
Just thinking.... when idling, is it normal for the electric fan to kick on.... like on our Fieros?
GreenPlatypus OCT 15, 04:49 PM
Heater core stopped up? Not sure if it has continuous flow through the core or not, but could be a possibility.
rogergarrison OCT 16, 10:20 AM
the elec fan kicks on at the right temp and shuts off like its supposed to.

heater and defroster both work fine.

Ive been my own mechanic for 40 years and I cant think of anything other than what Ive already tried. The normal operating temp of this car from serviice manual with a 160* stat is 175* ( shouldnt ever go above 180* w/ AC stopped in traffic), so elec fan should never come on unless the AC is operating.
GreenPlatypus OCT 17, 03:07 PM
Have you checked the temp sender? Could it be reading incorrectly?

edit: oops forgot about the part where the electric fan kicks on with the switch. keep forgetting it is an old car, more than 1 temp sensor/sender/switch. nevermind. i'll go back to my thinking.

[This message has been edited by GreenPlatypus (edited 10-17-2012).]

rogergarrison OCT 17, 07:04 PM
I bought an infared temp gun. It shows the engine temp as 175* +/- 5* on the heads, block, upper and lower radiator, and radiator hoses even though dash gauge says over 225*. Im assuming there is a few degree loss thru thru the hoses and metal parts. I did put a new temp gauge sender in to see what happens. Have to drive it somewhere in the next few days to see if its any different. I guess it could be even the gauge itself bad. If the sender dont seem to make a difference, ill try temp hookup of an aftermarket gauge. It is weird that the auto electric fan is supposed to come on with 225*/ AC and it does that according the dash gauge. I dont know how the electric fan sensor is wired...maybe to the gauge itself for all I know.
carnut122 OCT 18, 08:43 PM

quote
Originally posted by GreenPlatypus:

Have you checked the temp sender? Could it be reading incorrectly?

edit: oops forgot about the part where the electric fan kicks on with the switch. keep forgetting it is an old car, more than 1 temp sensor/sender/switch. nevermind. i'll go back to my thinking.




It was the sender on my mother-in-law's Dodge Dynasty. $14 and she was good-to-go.

[This message has been edited by carnut122 (edited 10-19-2012).]