My overheating persisted after head gasket change. I have determined my thermostat from LR is defective. It has been recommended by a well known senior member to try an after market thermostat.

Update; what I have determined about the LR thermostats; that they are like women; "I know nothing"

 

Hi, this is what I know: the after market thermostat I bought from AB is the exact same thermostat as the LR dealer sells. They are Identical. And it fails the same also. I have cured my overheating problem by bypassing the thermostat and everything is fine. I am going to keep the bypass until the investigation of the thermostat is completed and the problem resolved. If I hear anything I'll post.

Correction: everything is not fine, it was before I installed the new thermostat, but when I reinstalled my bypass unit the coolant would not flow through the radiator and the system always builds up what seems to me excessive pressure. The expansion cap does not release the pressure so maybe what I feel is normal pressure. If you plan to try the thermostat bypass; it is very important you read my "Service Bulletin No.1" posted below; it will save you some big time heartache. It's hard to get everything exactly right the first time. I thought I had it, but something else always seems to pop up. I do not understand how LR can take a literally reliable and simple American V8 and turn it into a freaking nightmare. A straight forward conventional cooling system would have worked fantastic. Instead they turn it into a spaghetti bowl of multi-port couplings and hoses; its just ridicules. Its like Wile E. Coyote decided to build an SUV to catch the Roadrunner.

Please read Service Bulletin; Updated 2/14/2011

 

So what's the deal on the thermostats? I have a new one in the package I got from British Pacific that is labled an AllMakes4x4 P/No PEM100990G. How can a thermostat be defective? They aren't exactly rocket science. I should be able to test it with a thermometer and some hot water before putting it on eh?

 

2001SE7, what did you end up doing to bypass the thermostat. I have a LR Dealer Thermostat in mine and as I have noted in the past, have some readings that are troubling to me off of the scanner, mainly at idle when the pressure valve in the thermostat cuts the flow to the radiator and sends it all through the heater core. Gauge reads fine but the actual temp runs up as high as 224. thanks Phil

 

Its not rocket science but it is LR science and we all know how f-ing retarded the engineers at LR are. No you cannot know for sure that it will be good if it opens in hot water; all of mine have opened in hot water. What you need to do for all of us before you install your new one is record the numbers on the housing that is cast by the inlet coming from the intake manifold gooseneck hose. So far all the of mine have the same number >PA66 GF30<. I have bought enough them, I am going to wait tell someone else finds one that works. The next step in this eval is to try an after market thermostat that has a different casting number. I hope yours is different. Thanks for your help.

 

Your thermostat is functioning exactly as it was design. You are good to go.

How I bypassed (which maybe the wrong term) First remove the thermostat. All the "pipes" in this setup are 1" galvanized. You need a "T", 90 deg elbow, and 3 2.5" nipples. some nylon thread tape and rubber pipe tape "wrap". Oh. the elbow has to be male on one end and female on the other. Wrap all the mating ends of the nipples and the male end of the "T" with the thread tape. Connect a nipple on both ends of the "T" straight thru. Put the "T" in a vise and tighten the nipples as you would torque in regular plumbing. While you are still in the vise wrap the center collar of both nipples with pipe tape (this will help seal the hoses). Turn the "T" horizontal in the vise and install the elbow in the center opening of the "T" and torque good and tight ending with the elbow parallel with The "T" straight thru then connect the remaining nipple to the elbow and torque then rubber pipe tape the center collar of that nipple. Your assemble should now look like a crude thermostat and should be obvious where to connect each hose. Slide the hoses on until they stop. Using screw type clamps; slide the clamps onto "humps" created by the pipe tape and tighten them good and snug. If the gooseneck hose is rubbing the alternator pulley remove the clamp and pull the hose up an inch and tighten the clamp. When you get it all back together fill the coolant as normal. Your Disco will now run without overheating. It isn't unusual to have an O2 sensor set the OBD right at first (mine did twice right a first but cleared and has come back so far). It is also normal to have low temp from the heater core until you start moving but blows warm quickly and will drop at stops but not much. I notice it more by the temperature gauge than from the cabin vents. Hope this was some help.

The operation of your thermostat you described is working exactly as it was designed so if you are not overheating don't touch anything or worry about it. i only described the bypass to help others that may need this setup to troubleshoot their thermostat failures.

 

Deleted: thermostat bypass not recommended. Use the fix discussed in "D2 inline thermostat mod ?" thread.