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  #16  
Old 11-24-2009, 04:13 PM
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Quote:
Originally Posted by toomany MBZ View Post
If the diaphragm is torn on the mono valve, you'll get heat all the time, is that okay?
I just replaced the mono in it - and ever since then the temp gauge has been 'acting' differently - could be coincidence in timing, or not...
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  #17  
Old 11-24-2009, 04:19 PM
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Quote:
Originally Posted by toomany MBZ View Post
If the diaphragm is torn on the mono valve, you'll get heat all the time, is that okay?
A common indication of a torn monovalve diaphragm is the heat not working at higher engine rpm's. The suggestion that a torn diaphragm necessarily results in constant heat is absolutely incorrect.
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  #18  
Old 11-24-2009, 04:22 PM
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Originally Posted by MercFan View Post
Yes - I get heat no matter what.... that's a separate problem - right now I think I've narrowed it down to a faulty cabin temp sensor - I'm working on sourcing a new one.
If you are getting heat in the detent "Cold" setting, the temp sensor isn't the culprit. The temp is not thermostatically controlled in either detent position.
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  #19  
Old 11-24-2009, 04:28 PM
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I just replaced my sender because the gauge started reading high and was a little jumpy. I spilled about a pint of coolant in the process.
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  #20  
Old 11-24-2009, 04:37 PM
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Originally Posted by andrewjtx View Post
With power not supplied to the monovalve, it should stay closed.
Is my mind playing games with me? I thought an unplugged monovalve gave you heat all the time?
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  #21  
Old 11-24-2009, 04:41 PM
Craig
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Originally Posted by kerry View Post
Is my mind playing games with me? I thought an unplugged monovalve gave you heat all the time?
You are correct, unplugging it will make stay open.
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  #22  
Old 11-24-2009, 04:57 PM
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You could have a stuck open t-stat, or a fail safe t-stat that remains open after failure. Also check the sending unit and the guage itself.
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  #23  
Old 11-24-2009, 05:22 PM
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Quote:
Originally Posted by rrgrassi View Post
Also check the sending unit and the guage itself.
How do I check them, plz?
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  #24  
Old 11-24-2009, 06:30 PM
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Originally Posted by MercFan View Post
How do I check them, plz?
I just replaced the sending unit based on a guess (after replacing the thermostat had no effect on the indicated temperature). The "normal" temperature on my gauge dropped from 95-100 to 85-90 with the new sender, which is closer to reality based on an inferred measurement. The old sender was also getting erratic. Before you replace anything, make sure you have a good electrical connection to the sender. High resistance will make it read cold.
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  #25  
Old 11-24-2009, 06:40 PM
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What if... a piece of the old mono valve had dropped into the coolant passages and got stuck inside the Thermostat!? I vaguely recall seeing the bottom of the old one thinking that there was something there that wasn't right - unfortunately I didn't save it.
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  #26  
Old 11-24-2009, 08:30 PM
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The monovalve should have little effect on how fast the engine comes up to temperature -- as was written in an earlier post, the volume of coolant in the heater circuit is small compared to the total amount of coolant. I would say that it is either something got into the coolant circuit during replacement of the monovalve and is stuck in the thermostat or something else happened and it's just a coincidence.

The sensor and the gauge can be tested with an ohmmeter. I don't remember off hand how many ohms a good sensor is cold/hot but probably a few hundred to a few thousand -- maybe someone here has done experiments. If the gauge works at all it is unlikely to be bad -- it's just a simple milliammeter movement and either works or doesn't work at all. Replacing the sensor is easy and not very expensive and is probably the second thing to do. The first is to pull the thermostat, make sure it's OK, replace if necessary.
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  #27  
Old 11-24-2009, 11:43 PM
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Quote:
Originally Posted by Jeremy5848 View Post
The first is to pull the thermostat, make sure it's OK, replace if necessary.
Yep - that's what I'm going to do... Thx all
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