Thermostat Stuck Open? - Defender Source
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  #1  
Old March 12th, 2006, 04:50 PM
johare
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Jay
95 D90 White ST
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Thermostat Stuck Open?

New Defender owner here. Its a 95 ST with 53k miles. On my maiden voyage from Denver back to Steamboat the temp gauge would go all the way to "cold" when going down passes (10min, no load, 65 mph). Outside temps were in the low teens. Driving flats or up passes, the temp gauge would read right in the middle. I'm also getting luke-warm heat and with the drafty nature of the vehicle, going over Rabbit Ears pass was freeeeezing. I've read several posts on heater core issues and I'll certainly investigate that as well but I would think that the thermostat should have closed the flow to the radiator below a certain temp and the gauge should have never read "cold." One other thing, in regard to the heater core, with the engine warmed up & running, I can squeeze the heater hoses with my bare hands and they are a bit soft. Thanks for and advice.
Jay
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  #2  
Old March 12th, 2006, 05:38 PM
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Hans Haase
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Hmmmm...... first thing that comes to mind is air in the system. Take off the raised fill plug on the heater hoses, up above the passenger side valve cover. If you don't see coolant up to the top, fill it till you do and squeeze the hoses (heater and radiator) a few times as well to work the air out. You really can't go by the overflow can to judge if the system is full or not.

When the truck is up to operating temps, the upper radiator hose should be hot and very solid. If it's something you can grab and hold onto it ain't hot enough. And if it's squishy and easy to squeeze, it's full of air and not coolant.

-Hans
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  #3  
Old March 12th, 2006, 07:12 PM
johare
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Jay
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I'll give that a shot. In terms of squeezing the hose, I was referring to the hoses going into the heater core, not the radiator hose. Thanks for the advice!
Jay
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Old March 12th, 2006, 07:35 PM
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True, but those should at least have some resistance to them as well while running. Since the heater hosesy bypass the thermstat, they would have flow through them no matter what the engine temp is. As the heater core is located kinda high up in the loop, a low coolant level or air pocket could possibly be in there as well. Especially if the overall level is really low. If that is the case, you wouldn't have any coolant up in the intake manifold..... which means heat wouldn't be transferred into it, and that is where the gauge sender is located.

-Hans
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  #5  
Old March 12th, 2006, 08:00 PM
johare
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Jay
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I just checked the fluid level - full. I removed the filler cap and a very slight press on the top radiator hose caused coolent to overflow. I see what you are saying about the source of the heater core fluid. Looking more like an issue with the heater core. The heater core has a "Genuine LandRover Parts" sticker on it. Would that inicate its a replacement?
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Old March 12th, 2006, 09:21 PM
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I had experienced fluctuations in heating temp and my temp guage creeping down when the vehicle was moving (generally fast) with little or no load in cold temps (~20F). I wound up putting on a radiator muff from RN and have enjoyed consistant temps and heat.

http://catalog.roversnorth.com/catal...101/page98.htm
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Old March 12th, 2006, 09:29 PM
johare
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Jay
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Cool! I'll take a look. I was thinking about experimenting with restricting the flow and this may be the ticket.
Thanks,
Jay
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Old March 13th, 2006, 11:24 AM
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Chris Estes
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Hi,

I'd try getting the air out of the system first, as that's free. I had a leak in my heater core that let a lot of air in. I figured things would be OK after that was fixed, but no luck. The engine would never get warm enough to make the heater blow anything but lukewarm. Sure enough, the thermostat was stuck open; the 'plunger' part didn't push straight out and had come out at an angle. One side got caught up and it would never close. My temp gauge hardly moves once the engine is warmed up!

-Chris-
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  #9  
Old March 13th, 2006, 03:06 PM
BarryO
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Barry O'Mahony
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I'm having the same problem with the Disco. The temp gauge has been reading a little high. But when coasting down a cold mountain pass recently, it got so low the Check Engine light came on. I'm pretty sure the thermostat is stuck in one position.
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  #10  
Old March 13th, 2006, 04:44 PM
johare
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Jay
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I'm taking this into the shop tomorrow for a few other things and I'll have my guy take a look and post what we find.
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  #11  
Old March 13th, 2006, 05:27 PM
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Robert Ragland
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Quote:
Originally Posted by johare
I just checked the fluid level - full. I removed the filler cap and a very slight press on the top radiator hose caused coolent to overflow. I see what you are saying about the source of the heater core fluid. Looking more like an issue with the heater core. The heater core has a "Genuine LandRover Parts" sticker on it. Would that inicate its a replacement?
If I am remembering the same sticker on mine, I believe it is more or less a notice suggesting the use of Genuine Parts as opposed to an indicator for the heater itself.
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  #12  
Old March 14th, 2006, 09:19 AM
johare
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Jay
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Consequences of an open Thermostat

So I dropped the vehicle off at the shop and discussed the thermostat issue with my mechanic. One of the main reasons this needs to be fixed is that the electronic fuel control uses engine temp as one of the variables in controlling the fuel injectors. If the engine is too cold because the tstat is stuck open, the injectors will stay on too long, using more gas than needed and unnecessarily carboning up the engine.
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  #13  
Old March 16th, 2006, 08:58 AM
johare
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Jay
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So, an FYI - we R&Rd the tstat and I now have great heat. The coolant temp warms to mid point in a few minutes (used to take almost 20) and stays there. Thanks for everyones input!
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