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Old 09-24-2006, 07:37 AM
crashone's Avatar
1983 300SD, 4 speeed
Join Date: Jul 2006
Location: Raleighish, NC
Posts: 664
Before and after running temps

What were your running temps before you changed out the water pump?
what were your temps like after you changed out the pump?

The reason I am asking - I flushed my block and radiator, refill with zerox g5, changed the T-stat, monovalve and the 3 hoses. My SD still runs the same temp (the needle stays between the top of the 80 and the 100? mark. I don't know how old the pump is and was wondering if there would be any improvement with changing the pump. In warmer temps with the AC on my temps range over the 100? mark. So maybe I answered my own question- When in doubt rip it out! (just kidding )

Hopefully someone has done this other than for complete failure of the pump. Thanks.

If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King

Ride in Peace Eric Peterson, Harley of Macon
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Old 09-24-2006, 11:27 AM
Join Date: May 2005
Location: CALIF
Posts: 508

1984 300d Turbo 140,000
Replace The Radiator, Check Mech Fan Clutch, Electric Fan,remove
Air, Add Water To Top Radiator Hose
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Old 09-24-2006, 11:32 AM
Join Date: Jul 2001
Location: Old Lyme, Connecticut
Posts: 3,595
I don't know about the rest of you guys, but I have never changed a water pump because of anything but a mechanical seal leak. To correctly diagnose your problem a little more data is needed, like, temperatures you reach at idle, temperature response to driving at highway speeds after the idle high temperature, A/C on and off for that cycle, and so forth. It also helps to turn the heat on full and see if that has an effect on engine temperature.

Cooling system performance is affected by nearly every feature of the system, so it is possible you have a worn out water pump. Before I assumed that I would boil the thermostat and check its response vs. temperature of the water, the condition of the A/C condenser and the radiator, as well as the space between them, and I would check the main fan drive. At some point MB started using viscous clutches activated by the air temperature coming over the hub (after going through the radiator). These things eventually lose the oil. There are threads on how to get a Toyota supplied dose to refill and how to do it, if that turns out to be the problem.

Good luck, and I hope this helps. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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Old 09-24-2006, 11:43 AM
Registered User
Join Date: Feb 2005
Location: Tuscaloosa, Alabama
Posts: 307
Take the radiator off and take it to a radiator shop.

They will flush it in a vat of cleaning solution and then check it for any pressure or leakage related problems. On an 83 model, there is a very good chance that crud has built up in the radiator. And with everything else you have replaced, you should be good to go. And if the car still runs at 100 C, and above during the height of summer, then it's probably a head gasket weakening. But weakening of a headgasket is not the same thing as a blown head gasket and you might can drive the car for as long as you want to drive it on a weakening head gasket, as long as you don't allow the engine to overheat. And I think the OM617 is more forgiving should you do allow it to over heat. Anyway, as long as the temp rises and STOP and holds steady at below 105 or so, you should be o.k.

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Old 09-24-2006, 12:18 PM
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Originally Posted by JimSmith View Post
Cooling system performance is affected by nearly every feature of the system,
I agree and this is the reason that the diagnosis of the cooling system is so difficult.

The SD has recently been running warmer. Instead of it's usual 90C., it creeps up to 98C. or so and then backs off to about 93C. Certainly nothing to worry about, but, clearly, something has changed within the system.

So, I change the thermostat, figuring that after 20 years, it's probably time.

Absolutely no change whatsoever.

Exactly why this occurs is somewhat of a mystery, however, I do believe that the return coolant temperature has quite a bit of influence. If the radiator is marginal (a definite possibility) or the fan clutch is marginal (also a definite possiblity), the return coolant temperature will be warmer than it would otherwise be.

One thought I have is that 95% of the thermostat is sitting within the return coolant flow. Only the very nosepiece of the stat is subject to the coolant exiting the head. Maybe the isolation of the nosepiece is not perfect and the thermostat responds slightly to the temperature of the return coolant.

Your thoughts appreciated.
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Old 09-24-2006, 01:36 PM
sailor15015's Avatar
Reverse lights! Score!
Join Date: Apr 2005
Location: Norman, Oklahoma
Posts: 1,184
Did you boil that new t-stat before you put it in? The seal on my water pump went out so I replaced it and while I had the system open I went ahead and did a complete citric acid flush. Well just my luck my t-stat failed closed during the flush so I spent a weak scratching my head trying to diagnose that. Just my luck it would go during the flush. Could that have caused it? Anyway, I get a new t-stat from Fastlane, stamped 80C. I boiled it and it doesn't start to open till 85, not fully till 90, the same actions the 87C t-stat out of my wrecked '85 showed. I got the new t-stat in and it worked great for two days, until today when my fan clutch went out! When I got the '84, the fan clutch was fused and turned all the time. The clutch from my wrecked '85 was still good so I put it in the '84. Worked great until this week of cooling system death. Before, my temps were pretty steady at 85C. I haven't had a chance to test them with a good fan since I just put it in a few minutes ago. With the bad fan and good t-stat, temps stayed pretty steady at 95C.


1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo
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