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Old August 28th, 2004, 02:51 PM
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Jon Strong
Join Date: Mar 2004
Location: Pennsville NJ USA
Posts: 98
replacing thermostat

Over heated yesterday just as I pulled into my garage, vent cap on the overflow resivior popped and was spewing steam and coolant. Just finished about a 12 mile drive, around 45-50 mph, no wheelin or tough driving. I didn't notice that the truck was hot until I saw the steam, and then saw the temp gauge nearin the orange line. I immediately shut the truck down, opened the hood, and tried to assess what had gone wrong. First thought I'd blewn a hose due to the ammount and sudden appearance of the steam, but looked for leaks every where, and the only source was the overlfow resv.

I've read all the over heat symptoms in the FAQ, checked the fan coupling, belts, clamps ,hoses, and the water pump is doesn't appear to have any leaks, and I have had no indications that there were any other fluid leaks. I had just done an oil change and air filter change that AM. Oil levels check OK, and no foam or indications of coolant in the oil on the dipstick.

The truck has run fine since I bought it in March this year, so I am taking a shot that its most likely a bad thermostat. This will be my first "repair" to the D-90 other than routine maint. I've done this before on other trucks/ cars, but I want to be extra careful with my D-90. Its in great shape, and I dont want to screw anything up.

So, basically I'm looking for anyone whose done this recently to chime in with any tips or precautions. I see that there is a temp sending unit in the top hose "goose-neck" that the thermo sets in. Should I replace this also ? Or is it just for the temp gauge ?


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Old August 30th, 2004, 12:24 PM
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Mike Hippert
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94 D-90 Grinding Rover
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Location: Manchester NH USA
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The T-stat is easy, besides the basics you need to make sure that the giggle pin in the T-stat is in the 12 O'Clock position so that any air bubbles in the system can get though when the T-stat is closed. When tightening the bolts that hold the housing on be careful not to go to tight as you are only going into aluminum. And you can check your T-stat by putting it into a pot of water on the stove, when the water reaches about 150*F it should open.

That one wire sender is just for the gauge and the gages have been know to go bad. You could check it by pulling the sensor out of the housing, attaching a ground wire to the side of the sensor and sticking it in a cup of hot water next to a thermometer, the gauge should read about 150*F at the 1/2 way and about 240* at the red. You will have to have the ignition on but the engine off.
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first then ask questions later! The loose nut behind the wheel
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Old August 30th, 2004, 01:32 PM
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Jon Strong
Join Date: Mar 2004
Location: Pennsville NJ USA
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thanks mike, just pulled the t-stat, no problems, just had to disconnect a few plug wires and move a vacum hose. Going to test the t-stat and make sure its the problem, new t-stat should be here tomorrow.
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Old May 25th, 2009, 04:53 PM
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Gore Ranger
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1989 RRC
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Location: Denver, CO
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hey guys,

I removed my radiator to flush the whole system and renew the fluid. I also decided to replace my thermostat since I think it was stuck open- it took forever for the vehicle to heat up. anyway, I removed everything a few weeks ago and I forgot which side of the thermostat points in? I know the jiggle pin goes at 12 o'clock, but I am not sure which side points in? In the attached picture, is the orientation of the thermostat correct?

Also, it is very difficult to get the housing back in and have the gasket stay in place. Is there anything wrong with using some black right stuff along with the gasket to get it to stay more easily?

Follow-up Post:

ok, I think that's correct since I read on the web that the spring should be on the block side. Can anyone confirm? I'd like to get this buttoned up...
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Old May 25th, 2009, 09:59 PM
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94 D90 ST #1247
Join Date: Jun 2008
Location: Flower Mound, TX
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I am thinking out loud, but it would make sense to have the spring on the block side. This is the piece which will heat up and release to open the thermostat...
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Old May 25th, 2009, 10:08 PM
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John B.
1991 Defender 90, 200TDI
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Yes, like that. A little sealer to hold the gasket is fine.
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