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  #46  
Old 02-01-2007, 08:18 PM
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I just don't buy the excuse that the temperature gauges are not accurate. It's easy to say, but I've never seen one that really was. All the gassers I've ever had sat right on the thermostat setpoint regardless of operating conditions. The Mercedes diesel seems to be a completely different beast that varies it temperature depending on load -- mine sits around 80C +/- 5C until I get up to freeway speeds, then it rises, and if I'm cruising up a hill, especially at high altitude, I can get close to 100C.

I also hear the thermal load for a diesel is higher, but I cannot understand how. A diesel is a more efficient engine, and in theory should shed less heat to the radiator as more heat is used doing work -- it has a cooler exhuast and better mileage than a gasser.

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  #47  
Old 02-01-2007, 10:01 PM
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So, what is the purpose of the arrow on the thermostat anyway? I used to think those were on the models which had the little bleeder valves in them but I noticed there is an arrow on the MB one I just removed even though it has no bleeder...why does the arrow need to point up? It seems like the thermostat is symmetrical and there is nothing special about it when it points up.
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  #48  
Old 02-01-2007, 10:12 PM
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Quote:
Originally Posted by nhdoc View Post

The MB stat I removed would spike over 100C and drop to under 80 during routine running...that's just wrong. The new Wahler behaves normally, the car warms up and the temp stays steady. These gauges are pretty accurate if they're working right, and this one is.

A car which runs at 90C+ is above its design temp. When new, these cars ran at just above 80C...a car running at 95C-105C means either the gauge is wrong or the engine is running warm. 80-85C is not cool...it's normal for these.
The SD has a brand new OE thermostat........Wahler.

It runs at 82-85C. when it's below 2000 rpm with a light load.

It runs at 90C. when at 2800 rpm at highway speeds.

It runs at 95-98C. when at highway speeds at maximum power (held for more than 30 seconds). It very slowly returns toward 90C. after 10-15 minutes.

I've checked the cylinder head and confirm that the head runs about 7C. cooler than the gauge.


Therefore, don't draw any firm conclusions on the capability of a 617 to maintain a perfect temperature under all conditions.

The 606 may be different.
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  #49  
Old 02-01-2007, 10:31 PM
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Brian,

I may be missing the point, but your SD does not sound as if it is controlling temp appropriately. While I can understand some increase in temp under heavy load, with appropriate air flow at speed the transfer should offset the increased heat load.

Something isn't right ... or, am I missing the point?
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  #50  
Old 02-01-2007, 10:33 PM
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Quote:
Originally Posted by stephenson View Post
Brian,

I may be missing the point, but your SD does not sound as if it is controlling temp appropriately. While I can understand some increase in temp under heavy load, with appropriate air flow at speed the transfer should offset the increased heat load.

Something isn't right ... or, am I missing the point?
Well, it has a brand new water pump, a brand new thermostat, it behaves in an identical manner whether the ambient temp is 0F. or 95F...........so, if it's not behaving properly, I'm willing to listen to all rational ideas..........

You can't condemn the radiator if the performance is identical at 0F. It's the only item in the system that is "aged".
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  #51  
Old 02-01-2007, 11:04 PM
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Hmmm - was the temp maintained in the same manner prior to all the replacements? Prior to the new tstat?
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1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #52  
Old 02-01-2007, 11:16 PM
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Quote:
Originally Posted by stephenson View Post
Hmmm - was the temp maintained in the same manner prior to all the replacements? Prior to the new tstat?
It was absolutely identical with the old stat.

However, it has changed behavior over the course of the last eight months or so. Previously, it would very rarely climb above 90C. The ambient would have to be very high. Now, it climbs to 95C. just about every day..........
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  #53  
Old 02-02-2007, 02:22 AM
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Quote:
Originally Posted by tobybul View Post
Based on the performance of my 84D (aftermarket rad) vs my 85D (oem rad), I beleive that the oem rad does not cool as well. The cooling performance of the rad has a direct bearing to the engine temp. I don't think this means that the oem rad is no good. Its just the the non-oem maybe more efficient (more surface area?).
I've had my original radiator and it was replaced with an aftermarket Nissins one, and still, the temp runs the same with the same thermostat.

Of course, when the thermostat went bad a few days after we got the car in 2004, the temp would soar to 100 on highways.

Replaced it with what I think is a Wahler brand, and it sits just above 80, maybe 85 to 90.

This is consistent regardless of outside temp too, and even the fan replaced with a good used one.
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  #54  
Old 02-02-2007, 09:13 AM
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Quote:
Originally Posted by Brian Carlton View Post
It was absolutely identical with the old stat.

However, it has changed behavior over the course of the last eight months or so. Previously, it would very rarely climb above 90C. The ambient would have to be very high. Now, it climbs to 95C. just about every day..........
i would suspect your rad.

tom w
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  #55  
Old 02-02-2007, 09:15 AM
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Quote:
Originally Posted by Old300D View Post
I just don't buy the excuse that the temperature gauges are not accurate. It's easy to say, but I've never seen one that really was. All the gassers I've ever had sat right on the thermostat setpoint regardless of operating conditions. The Mercedes diesel seems to be a completely different beast that varies it temperature depending on load -- mine sits around 80C +/- 5C until I get up to freeway speeds, then it rises, and if I'm cruising up a hill, especially at high altitude, I can get close to 100C.

I also hear the thermal load for a diesel is higher, but I cannot understand how. A diesel is a more efficient engine, and in theory should shed less heat to the radiator as more heat is used doing work -- it has a cooler exhuast and better mileage than a gasser.
all you say is true, but the rads are sized accordingly. so if the rad is just big enough to handle normal op temps a load will bring up the temp.

they dont make them overly big cause of weight, i believe.

tom w
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..I also have a 427 Cobra replica with an aluminum chassis.
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  #56  
Old 02-02-2007, 11:37 AM
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While we are on the subject of cooling,,, try blowing out your radiator fins with compressed air . Apply the air from the back , fan side. I was amazed at the amount of crap that came out of my 79SD..

I have to do this all the time with my tractors when I am bush hogging.. My tractors have screens to catch the big stuff , but a radiator will get clogged with dust over time.
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  #57  
Old 02-02-2007, 11:48 AM
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Quote:
Originally Posted by t walgamuth View Post
i would suspect your rad.

tom w
If the rad was marginal, it wouldn't hold 95C. at 98F. ambients.

The fact that the performance is identical, independent of the ambient temp. would effectively rule out the rad.........don't you think??
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  #58  
Old 02-02-2007, 12:32 PM
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Quote:
Originally Posted by stephenson View Post
What if tstats had evolved the same way - imagine a sensor based electric system that measured water in 3-5different places, also using inputs from other thermal sensors and position sensors to anticipate loads so that as you start up a hill, the tstat opens in advance of the load -maintaining temp +/- 1 degree ALL THE TIME. If it is gonna be electric, why not make the coolant pump electric, too (I think this is already in the works with move to higher voltage systems) - and then the pump could work with the sensor system and the tstat to completely control thermal issues without belt drive - it could even operate off the battery when the belt does through itself .... pretty cool!
They're working on that now.... automakers are trying to get every last bit of MPG out of their big engines (one day they will figure out small displacement and turbos....), and the system you've described is one of those efforts. Why take HP (as little as it is) to pump water when you don't need to? IIRC, a big beneifit of an electric water pump is also to allow the engine to warm up quicker (and that is an emissions requirement).

Actually, I think there is a production vehicle with an electric water pump already... the Colorado maybe? Don't know if it has any funky control algorithm though.
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  #59  
Old 02-02-2007, 01:32 PM
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I have had thermostat problems too. My thermostat that the car had when I bought it started to fail and kept temps from exceeding 60 degrees C. I replaced it with a new one and it would seem to hold temps at 85 degrees C. The previous one used to keep temps at just above 80. The new one started to fail recently and its not even a year old. If I keep my heater on full blast I can still maintain about 83 degrees C temps in the winter. If I turn it off however the temps slowly climb to 100C. Temps rise to the 80 degree range quickly then creep up slowly from there.

I have bought a new one from napa. Last night I drilled 3 3/32 holes around the edge in the new one. This will provide some flow but it won't interfere with warm up much.

I do have something to say that I haven't seen stated here yet. If you have an engine that has run at 80 degrees C all its life and you change thermostats to one that causes it to run at 90, it will cause excess wear due to thermal expansion. You want a thermostat to hold a temp closely no matter what to limit this.
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  #60  
Old 02-02-2007, 11:48 PM
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Brian,

Perhaps the fan clutch? Have heard of a lot of radiators being replaced with no real change ...

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1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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