New engine, few raadiatior swaps, overflow tank (but replacement was used), Never smell fluid inside, don't seem to lose much.

No matter what, interstate travelling I am at 100degrees (unless heat is on and then it drops to 98 or so.

Suggestions?

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Are you sure the sender is working properly? How about the thermostat?

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

Same issue-

-New Behr Radiator
-New water pump
-New thermostat
-Full citrus flush

Even when I'm going up a serious incline, it doesn't raise above 100, so I think I'm fine. One of these days, I'm going to shoot the engine with a heat sensor to see if the head's temp sensor is accurate. Otherwise, I'm not worrying. More efficient engine than if it were running at 80, anyhow.

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New engine, at least a different one. Same behaviour. I am going to by pass the heater core and aux pump today with a long hose and see if its internal somewhere. I have a 800mile round trip this weekend to the beach and it might get a bit warm down there.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

If you bypass those and don't block it, the problem will be worse, not better. As long as the heater control valve is closed, no need to play with that circuit.

Is the bleed line on top of the radiator free-flowing?

Sender or gauge calibration, almost certainly. The thermostat is regulating the temperature, otherwise it would rise higher the 100 on a hot day or an extended hill climb. The cooling system is able to reject all the heat required to stay where the thermostat regulates it. You didn't say that you replaced the thermostat, but with all that other work I am assuming you did and things didn't change. It is the correct t'stat, yes?

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1987 W201 190D

Ok, I see what you are saying. Your old engine read 100C and the new one reads 100C as well.

I suggest you get an infrared thermometer. You can get them at Harbor Freight for $30. This should let you know if you are really having a problem or not. And if so, it may help pinpoint the problem.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96451

I know the chances of two senders being bad is small, but it is not out of the question. When mine went bad it read hot all the time. It could also be something in the wiring causing it to read bad in both engines.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

There is a lot of rubber, joints and electronics between where it comes off the engine to the aux pump and where it feeds back into the engine from the firewall around the oil filter. This is the only area that has not been replaced.

The sender is used I think I am going to come into work late and pull a new used one and a nearly new expansion tank I saw at they yard last weekend.

The hose should be clear, it is fairly new (replacement).

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Yes, BUT all of that doesn't matter if the coolant isn't flowing through there. All that's necessary is for the heater control valve to stop the flow. You're wasting your time (and making it worse) if you bypass it without blocking it.

I agree with the suggestion that "you get an infrared thermometer" I took mine on a road trip last summer and found that the overheating problem with my "85" was the gauge, A good "smack' on the left side of the dash cured it.

You will use this tool again even it doesn't help on this particular problem.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Make sure your coolant cap is holding pressure. Should be around 14-17 psi. Low pressure could cause high temperatures.

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1983 123.133 California
- GreaseCar Veg System

Remember that the temp gauge is merely a voltmeter. If the gauge is bad, or if the gauge is not getting proper ground, or if the sender isn't getting proper 12v, it will not read correctly.

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Gone to the dark side

- Jeff

so true.

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+1

I had the same issue. Bought HF IR temp gun....measured head temp....realized the sender was off calibration....new sender, problem solved.

Those HF temp guns are really useful for all sorts of other things too.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Don't forget to burp the system of any air...

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