Re: Overcooling - Defender Source
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  #1  
Old December 7th, 2009, 12:16 PM
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phil
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Re: Overcooling

As a follow up to a previous post, the temp gauge on my d90 showing the temp very low, in the fall with milder temps it ran 1/4 ways to the norm of mid way. Now with colder temps outside its barely moving up if at all.
As suggested by some I changed the thermostat. The thermostat that was in there was fine from what I can see, nevertheless I changed it. So the problem persists.
Just to mention, the truck runs fine, appears to idle a little too rich when accelerating initially in 1st & 2nd gear.
Also, I made sure there was no air in the system and appears to be well under pressure when truck running.
It does not seem to be the gauge itself, since it does move, even if minimally. Could it be the coolant thermo sensor??? From what I understand, the sensor sends temp data back to computer, so if faulty could it be telling that the coolant is cold and that would reflect on the gauge???
Has anyone had this issue with their 90? also, is the coolant temp sensor located on the housing where the thermostat is? just top left of the coolant hose???

thanks all for any input.....

cheers

phil
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  #2  
Old December 7th, 2009, 01:57 PM
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Charles Galpin
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This doesn't sound right, although I'm not sure about a stock gauge. I have a VDO and mid way is about 190. If the thermostat is working, it should warm up to about 200, then cool down to whatever "normal" is. I think that's the right location for the sensor. Check the wire is not loose and make sure the gauge is grounded.

My D90 currently runs too cool since my fan clutch is stuck engaged and I haven't gotten around to replacing it. I am curious what's too cold for our V8's though. Mine is hovering around 186-188 I think.
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Old December 7th, 2009, 03:50 PM
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The engine is running hot, the hood after driving is real hot, so it seems to be running at temperature. Just now I drove it to pick up my son and same thing, the temp is all the way down, came up to midpoint/ 12 o'clock area for a minute then right back down. Engine does seem to be running smooth and interior heat is good.
I checked the sensor I mentioned and cleaned both connections (has 2 yellow wires plugging into it) appeared ok..... even checked sensor below it, though not sure what that is for. Where would the ground for the gauge be?
thanks again
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Old December 7th, 2009, 04:20 PM
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Charles Galpin
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The gauge will be grounded near the gauge (you'll need to pull the instrument cluster but it's easy).

But your last description makes it sound like it's working more like normal than you originally described. Not sure what else to consider here. Infrared thermometers are real cheap now and it would be worth verifying the reading against actual temperatures at the sensor.
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Old December 7th, 2009, 04:55 PM
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Ironically enough, the gauge has only moved today after I posted. Otherwise it really had not moved more than a fraction in days, which I associated with the sudden arctic NY temps we just were hit with. Before that would come up & go down, more likely would be at midpoint when driving local, in highway would usually stay low. Sorry about the confusion.
SO, next is going to be check ground in dash and hopefully get a infrared thermometer..... what do you test anyway with the thermometer? the engine block?
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Old December 7th, 2009, 05:20 PM
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Charles Galpin
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You aim it at the upper radiator hose housing or where the temp sender is. But you'll find yourself measuring everything else just for fun. At least on my truck the heads, manifold, and block temps vary wildly depending on where you check.

Maybe someone else can chime in on your temp situation. Kind of sounds normal to run cooler at highway speeds in cold weather. Maybe you just need a muff.
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Old December 7th, 2009, 05:28 PM
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Is your fan clutch seized and running all the time ... this will overcool the engine.

get a rolled up news paper and try and stop the fan spinning when the engine is running but cold ...
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Old December 7th, 2009, 05:31 PM
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Charles Galpin
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You would know if the fan clutch is seized. It sounds like a jet engine taking off and never kicks off. I know because mine.
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Old December 7th, 2009, 06:00 PM
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yes, the engine fan is running all the time...... but why would the temp fluctuate at times?

Follow-up Post:

Quote:
Originally Posted by cgalpin
You aim it at the upper radiator hose housing or where the temp sender is. But you'll find yourself measuring everything else just for fun. At least on my truck the heads, manifold, and block temps vary wildly depending on where you check.

Maybe someone else can chime in on your temp situation. Kind of sounds normal to run cooler at highway speeds in cold weather. Maybe you just need a muff.
Muff??? I figure at highway cooler, but not at below..... last few days not much difference on gauge while hot & running and cold......

Does anyone know if faulty sensor can give off these symptoms????
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Old December 7th, 2009, 06:31 PM
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Charles Galpin
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Because as your RPMs vary the fans pull more or less air through the radiator. Like me, you should replace the clutch fan or get those flex fans and adapter. I just have been meaning to see if mine will be covered under warranty, and if it is I'll try another. If not, I'll go the flex fan route I think.

I could be wrong but a bad ground is more likely to give a wrong reading in general or fluctuate randomly but not what you describe.
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Old December 7th, 2009, 07:34 PM
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There are actually 2 coolant temp sensors, and one switch, on the top of the engine. One for the gauge, one for the ECU, and a switch for the A/C fan system. There is no connection between them, the gauge is totally independent from the computer and vice versa.

You want the sender that's just below and to the drivers side of the thermostat housing, that threads in from the front of the intake manifold. Sounds to me like either a bad sender or a bad gauge, best bet is to get in there with an ohmmeter and testing what the sender resistance is. I just don't remember where to find a resistance chart for this particular gauge, which is of course not a standard resistance curve.

-Hans

p.s. Just for posterity sake, the temp sensor for the computer is on the top front of the intake manifold, toward the drivers side and threads in from the top.

The connectors on the thermostat housing are for the A/C system fan control, if you don't have A/C the switch isn't connected. (Great source for electric fan temp control)
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Old December 7th, 2009, 07:56 PM
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Didn't realize there was 2 sensors..... seems likely that it can be a sensor just sending wrong data. I think the engine coolant sensor is cheap enough to wing a swap and hope for a fix. What's the other sensor called?
or are they both the same just different functions? would this be it??
http://www.roverparts.com/Parts/ETC8496.cfm

Thanks for all the advise......
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