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Discussion Starter #1
Why would my temperature run hotter after a new water pump was installed?

I just had my water pump replaced by my local Mercedes dealer. They also changed the hoses and the serpentine belt. While they were at it, they flushed the entire system and of course they refilled it with all Mercedes liquids.

On the way home, I noticed that my car is running 5 or 10 degrees warmer. I’m sure you guys know that the actual temperature is only indicated at 80 and 120 and that there is just a mark in between that I think is 100 degrees. My car always ran just above 80. I would say it was 85 degrees, except on very hot days or when sitting in traffic after running long and hard, when the temperature would creep up toward 100 and the fans would kick in to bring it down. Now my car runs closer to the 100 mark than to the 80 mark. I would say it is running at 95 and sometimes a little lower in the middle of the marks at about 90.

Why would my temperature run hotter after a new water pump was installed?

I am sure that more heat cannot be a good thing. For example, my oil pressure usually was lower when my car ran hotter on hot days in the past and sure enough, my pressure was slightly lower yesterday. They also changed the oil and filter and I suppose they may use slightly different weight oil for the summer, although I did not make any such request. My car is always maintained at the dealer and I have been faithful about changing the oil in between every scheduled 7500-mile check-up. My oil is always a nice golden color. It has never been black.
 

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2002 CL55 AMG, 1993 190E 2.3L, 2004 SLK320 Sport
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Check thermostat, it might not be opening properly?
Since you did all this work, I would change thermostat too!

http://www.thebenzbin.com/mercedes_thermostat.html
Check out this link!
Good luck,
Spiros
p.s. Great occupation!
 

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Discussion Starter #3
I did get a new thermostat and on another forum a member had a similar experience when he replaced his thermostat. Maybe my old thermostat was just not working very well, but I think I like the idea of running a little cooler. My car has not reached 100, so I guess I am in the safe operating temperature range. I just liked it better when it was a little cooler.

Thanks for your reply
 

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1994 E320
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Some air hanging around in the system that hasn't been bled after the refill? A loose belt? Or maybe merely a faulty temperature sending unit. Check those out too.

Hope this helps,
Shady
 

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E320 wagon
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Check all your fan / ducting , I second the trapped air in the system . Give it a week to get bled out or over fill / add to it when cold. Mine did the same .
 

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Discussion Starter #6
Thank you for the tips. I like the air idea, because I thought I saw a little gurgling in the plastic overflow tank where the recalculating liquid enters the tank. On the way home on Friday, my car was running just a little cooler, although it was not quite as cool as before they installed the new pump and thermostat.

Does running the motor with the cap off, help the system purge the air from the system?
 

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1994 E320
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Ksing,
The way to do it is to disconnect the hose that runs from the top of the radiator (or thermostat housing on some cars) to the reservoir at the latter's end, and running the engine at idle until a steady stream of coolant comes out. The hose will spit some air bubbles at first. Just point the hose into the reservoir's opening to prevent losing any coolant, and be careful not to burn your hands!

Hope this helps,
Shady
 

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SL320, 300e, 450SL
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Ksing, ask them what thermostat they put in. They could have put one in different than you had originally that opens up at a higher temp which could be part of the new crusing temp youre citing.
 

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Depends on the day!
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I know on the M103's there is a series of bolts on the drivers side of the valve cover that are there to bleed the system, as well as one on top of the t-stat housing.. It's been a while since I looked at an M104, but it might be worth a look.

Good Luck!
Jonathan
 

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Discussion Starter #10
Cool Thermostat

bc2885 - 4/23/2005 9:38 AM

Ksing, ask them what thermostat they put in. They could have put one in different than you had originally that opens up at a higher temp which could be part of the new crusing temp youre citing.
I thought the thermostat temperature rating had more to do with the holding the water in the block during the initial heat-up of the motor and how soon the heater would work on a very cold day. I didn’t think the thermostat had all that much to do with normal operating temperatures. It is hard to believe that the thermostat would be closed all of the time during normal operation.

Would a lower temperature thermostat really maintain a continuously lower operating temperature? If it would, then why would anyone want a hotter motor? My way of thinking is that more heat must be a bad thing for things like my gaskets, wiring harness, oil life, and overall engine life.

I am definitely going to ask about getting a lower temperature thermostat, if it would reduce the normal operating temperature of my car.
[8D]
 

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RE: Cool Thermostat

Would a lower temperature thermostat really maintain a continuously lower operating temperature? If it would, then why would anyone want a hotter motor?
Yes it would, but only at cruising speeds. In heavy stop-and-go traffic or with the engine idling for extended periods (and especially with the AC on,) though, the thermostat is as good as not being in there at all.

My way of thinking is that more heat must be a bad thing for things like my gaskets, wiring harness, oil life, and overall engine life.
Not necessarily. Actually a "hotter" thermostat means better & more efficient combustion (i.e better mileage) and a smoother running engine, maybe even longer engine life (up to a limit, of course - I wouldn't want to use a 91C thermostat in Saudi Arabia, for instance [:D])

Hope this helps,
Shady
 

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2006 S500 AMG Wifes Rig Hillbilly Girl 02 ML320
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I am definitely going to ask about getting a lower temperature thermostat, if it would reduce the normal operating temperature of my car.




It will reduce your temp! The therm is going to open and close to maintain a hopefully constant temp in the motor! The hotter is gets the more open it becomes and lets in cooler water from rad! The cooler it gets it closes to bring the temp up! So the lower the therm temp the cooler it will run!![;)][;)][;)][;)]

Smokie
 
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