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2006-2009 Range Rover MkIII / L322
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Discussion Starter #1
About 2 weeks ago I got the dreaded (not really) P0128 slow to come up to temperature code, which set the MIL on, and the truck was really slow in coming up to temp. So I did the normal thing and replaced the thermostat with a new one (I do have 175K miles on the truck) and it seemed to warm up just fine for one driving cycle, then did the same thing. I took the old thermostat dropped it in boiling water and it did not move at all (didn't push the center pin out) so it appears that the thermostat was actually dead. This morning I drove it to work (as I do every day) and after 12 miles on the highway and about the same on back roads running at about 45 MPH I used my IR thermometer on the transmission oil pan and got 130F (F, not C) in a few places around the bottom of the Tranny. That seems really low to me (like about 50F low). The engine does heat up after about a mile on the highway, but according to the OBDII scanner I have it only gets up to the high 180's of very low 190's (again F, not C). I'm going to ASSume that the new thermostat is working correctly but I will check it before I pull the transmission/oil cooler thermostat and replace that one as well.

Does this sound like a stuck open Oil cooler/Trans Cooler Thermostat, or can a stuck engine thermostat result in lower transmission temperatures as well?
 

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Re: 06 HSE RUNNING COLD - TRANSMISSION at 130F AFTER 25 MILE

I had the same thing on my '06 HSE and first replaced the thermostat, but no luck. Replaced the Oil Cooler Mixing Valve (OCMV) and all is good. Do it.
 

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2002-2005 Range Rover MkIII / L322
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Re: 06 HSE RUNNING COLD - TRANSMISSION at 130F AFTER 25 MILE

Did you test the old mixing valve part?
 

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2006-2009 Range Rover MkIII / L322
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Discussion Starter #4
Re: 06 HSE RUNNING COLD - TRANSMISSION at 130F AFTER 25 MILE

Not yet, have a brand new one sitting on the kitchen table, just seems weird that both of them went bad at the same time. Maybe the engine thermostat failed awhile ago and a working OCMV masked it, and then the OCMV failed. The engine thermostat was definitely bad, I did test it when I put the new one in.

Not much sense in testing it at this point, since if it is bad I need a new one and if its not, then it has to be my new thermostat that I just put in, either way I have to drain and refill the cooling system to replace it or test it, so I might as well only do that once. I'll test it after the new one is in.
 

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2010-2012 Range Rover MkIII / L322
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Re: 06 HSE RUNNING COLD - TRANSMISSION at 130F AFTER 25 MILE

I didn't drain my system when I replaced the thermostat. Just popped the housing cover and replaced it. The ran the engine and topped up if required. But perhaps you're doing something additionally. This was on a 4.4L V8 LR3.
 

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2006-2009 Range Rover MkIII / L322
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Discussion Starter #6
Re: 06 HSE RUNNING COLD - TRANSMISSION at 130F AFTER 25 MILE

Yes the OCMV is down on the very bottom left corner of the radiator it looks like a section of radiator hose with a T fitting in it and controls the temperature of the water to the oil and transmission coolers. Its in parallel with the main engine thermostat, when it fails it acts just like a stuck open engine thermostat. I already replaced the engine thermostat and only lost a quart or so of coolant. The OCMV replacement requires the whole radiator to be drained.
 

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Re: 06 HSE RUNNING COLD - TRANSMISSION at 130F AFTER 25 MILE

Oil Cooler Mixing Valve (OCMV) from post 2
 
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