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  #1  
Old 06-16-2015, 03:01 PM
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Sudden Jump to 120*C and Then Jumpy Needle

Going down the freeway, think I hear something, check my gauges, and see coolant temperature is at about 120*C. Keep a real close eye as about right on and not in the red. I soon see it cool to just below (110*C?), then jumpy. When I go a short ways on surface streets and the needle really starts jumping and twitching. Once got near my home was now bumping into 120*C, but not going over. Let it idle to cool the turbocharger, but since don't have a shroud and was going a little up, shut down. I then look under the hood and find no obvious leaks; just got home from pressure washing the engine compartment. Any ideas?

Thank y'all for the help in advance!
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  #2  
Old 06-16-2015, 03:14 PM
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Quote:
Originally Posted by Adriel View Post
Going down the freeway, think I hear something, check my gauges, and see coolant temperature is at about 120*C. Keep a real close eye as about right on and not in the red. I soon see it cool to just below (110*C?), then jumpy. When I go a short ways on surface streets and the needle really starts jumping and twitching. Once got near my home was now bumping into 120*C, but not going over. Let it idle to cool the turbocharger, but since don't have a shroud and was going a little up, shut down. I then look under the hood and find no obvious leaks; just got home from pressure washing the engine compartment. Any ideas?

Thank y'all for the help in advance!
Good thing you threw in the "just got home from pressure washing " comment. More than likely a wire was severed from the coolant temp sensor. I did similar when changing GP's. I think it is the one between cyl 2 and 3 below gp's. I will double check if no comment from a known source here.
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Old 06-16-2015, 03:17 PM
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Originally Posted by sloride View Post
Good thing you threw in the "just got home from pressure washing " comment. More than likely a wire was severed from the coolant temp sensor. I did similar when changing GP's. I think it is the one between cyl 2 and 3 below gp's. I will double check if no comment from a known source here.
Oh dear... I thought I was careful. I will check after lunch; ran out of calories during the wash.
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  #4  
Old 06-16-2015, 04:20 PM
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Checked all three temperature sensors, and none have any damage, except one when the boot crumbed in my hand. Gauge now reads 60*C.

Checked for any other damage, and find none.
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1985 Mercedes-Benz 280TE - Current project and hopefully by mid May daily driver.

1985 Mercedes-Benz 300TDT - Rear ended 23 September 2016.

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  #5  
Old 06-16-2015, 04:44 PM
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Just give it a few days to dry out, then see what happens. Weird things can happen when electrical connections get wet, and everything gets wet when you pressure wash the engine compartment.
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  #6  
Old 06-16-2015, 04:56 PM
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Originally Posted by Left Coast View Post
Just give it a few days to dry out, then see what happens. Weird things can happen when electrical connections get wet, and everything gets wet when you pressure wash the engine compartment.
Thank you for the reply!

Yes, forgot about that. Next time I have a reason to go out is Thursday, so should be dry then, right? Then if still acting up, guess Friday draining the coolant and putting in flush.
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  #7  
Old 06-16-2015, 05:34 PM
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Spraying with wd40 will drive the moisture out if needed. You may yet have to check the connection or replace the sender itself but think not.

No indication you need a coolant flush incidentally.
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  #8  
Old 06-16-2015, 06:13 PM
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Originally Posted by barry12345 View Post
Spraying with wd40 will drive the moisture out if needed. You may yet have to check the connection or replace the sender itself but think not.

No indication you need a coolant flush incidentally.
Oh yes, Water Dispersant-40.

My thinking is something came loose and blocking a passage. Do have coolant disappearing and a moldy smell in the passenger footwell. But, Tram said not to worry, so not. The rusty water seems to be mostly gone, but now has me wondering.
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  #9  
Old 06-17-2015, 12:43 PM
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No sense overthinking this one. Sensor wire connection or sensor itself are the prime considerations. Make sure you identify the right sensor.

Of course in life there are always the remote unexpected things. On average though in a situation like yours you can almost ignore them.
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  #10  
Old 06-17-2015, 01:31 PM
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Originally Posted by barry12345 View Post
No sense overthinking this one. Sensor wire connection or sensor itself are the prime considerations. Make sure you identify the right sensor.

Of course in life there are always the remote unexpected things. On average though in a situation like yours you can almost ignore them.
Barry, thank you so very much for the help!

Okay, I tend to do that with my condition.

The sensor can be checked by unplugging, right? Or is there redundancy?Do know the sensor for the glow plugs isn't 100 percent right, but have a method around that.

I will ignore them for now.
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  #11  
Old 06-17-2015, 03:17 PM
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Some people put too much trust in gages. There is no physical way that the coolant (and sensor body) could truly vary in temperature fast enough to make the needle "twitchy". Maybe 1 sec oscillations max.
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  #12  
Old 06-17-2015, 05:32 PM
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Sure sounds like the coolant temp sensor wire. Could be wet, could have a bare spot, or a broken conductor. The sensor completes the gauge's circuit to ground through a temperature variable resistor. Intermittant connection (broken wire) = twitchy gauge. Short to ground (bare wire) = pegged temp gauge needle (hot). Diesels tend to shake, and that flex's the wires. Good luck.
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  #13  
Old 06-18-2015, 12:16 AM
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Why I suspect the connection or sensor wire as well as mentioned. Fresh water is not electrically conductive unless something like salt or another contaminate is in it. Now the blast pressure of pressure washing could shake up an old wire or connection easily enough.
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Old 06-18-2015, 02:42 PM
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I have had the same symptoms when the alternator body was not getting a good ground, or the body to block cable connection was bad... GROUND is needed for the sensor to work right!
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  #15  
Old 06-20-2015, 04:39 PM
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Thank y'all for all the help!

Quote:
Originally Posted by BillGrissom View Post
Some people put too much trust in gages. There is no physical way that the coolant (and sensor body) could truly vary in temperature fast enough to make the needle "twitchy". Maybe 1 sec oscillations max.
Bill, actually, I use them to trend and give a rough picture. If the gauge says the engine is running hot, see if gets higher. It didn't, so kept driving. If I trusted the gauge, would have immediately pulled over.

At first, the swings seemed to be logical as responded to the terrain. However, down the ramp and onto surface, got wild. Bet the water moved.

Quote:
Originally Posted by Charlie Foxtrot View Post
Sure sounds like the coolant temp sensor wire. Could be wet, could have a bare spot, or a broken conductor. The sensor completes the gauge's circuit to ground through a temperature variable resistor. Intermittant connection (broken wire) = twitchy gauge. Short to ground (bare wire) = pegged temp gauge needle (hot). Diesels tend to shake, and that flex's the wires. Good luck.
Charlie, yes, by the connecter there is a bare section from manufacture and the plastic shrinking. Can you still get the boots?

Quote:
Originally Posted by barry12345 View Post
Why I suspect the connection or sensor wire as well as mentioned. Fresh water is not electrically conductive unless something like salt or another contaminate is in it. Now the blast pressure of pressure washing could shake up an old wire or connection easily enough.
Barry, yes, as I said, bare wire due to the boot disintegrating.

Quote:
Originally Posted by vstech View Post
I have had the same symptoms when the alternator body was not getting a good ground, or the body to block cable connection was bad... GROUND is needed for the sensor to work right!
Thursday was out all day, plus most of today, and the gauge showed logical readings, not getting a little over 80*C. So, think all that happened was temporary, right?
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1985 Mercedes-Benz 280TE - Current project and hopefully by mid May daily driver.

1985 Mercedes-Benz 300TDT - Rear ended 23 September 2016.

1979 Mercedes-Benz 300TD - Parted out.

1971 Volkswagen Sunroof Squareback with F.I. - in need of full restoration.

1971 Volkswagen Squareback automatic with F.I. - Waiting on logistics to get to Texas.
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