Hello friends just like the title says I have a 2003 discovery. 89k miles.

I pulled the engine and did a repair on the slipping cylinder sleeves. FYI, I no longer have any ticking.

Before pulling the engine, I noticed it was running hotter than I was comfortable with… In some cases 220°+. While I was doing the work on the engine, I replaced the entire cooling system, including a new radiator, new water pump, new 180° thermostat, new heavy duty clutch fan and heavy duty Dorman fan. I had the entire engine out so I know the coolant passages were empty and free of coolant, although I did not do a flush of the block.

After putting it together, I’m having the same issue of it running very hot. I’ve noticed that the bottom hose below the (third!!!) thermostat that I’ve tried is cold. The top hoses are pressurized and hot to the touch. There’s a drastic difference between the top and the bottom below the thermostat.

Having felt that difference I assumed the thermostat was bad but after the third one and having the same issue, considering all the new parts, I’m at a loss.

There are a ton of threads on this forum and otherwise about it, but I’ve never seen any real resolution to this other than replacing the things that I have already done.

I feel like even if the block is cracked, the coolant still should be flowing and I would assume would be slightly cooler at the bottom but not cold as it is.

I’ve double checked the serpentine belt routing and everything seems to be OK. I also replaced the air conditioning condenser fan with a new one since like all of them, the original one was seized with a fuse blown.

I feel like I have done absolutely everything you can do.

Does anyone have any suggestions as to why that lower pipe is so drastically colder than the top after running it down the road 5 miles?

FYI, I do get heat when I turn the cabin fan on and actually I noticed that helps bring the temperature down a couple of degrees on my Ultragauge.

 

Well if I was you I would spend 100.00 and put in the in-line thermostat. Install the kit without the thermostat and see where your temps are. The problem with the stock thermostat is you can not remove the thermostat to to do any further diagnostics.

With the thermostat at the bottom until enough Hot coolant flows to hit the thermostat you can have exactly what you described. Those 180 stock thermostats are notoriously unreliable due to bad quality control. The one I had in my disco when I bought was closer to a 190 than 180.

My gut is you might have a cracked block, the pressurized hoses are a clue, doing the inline as above will get you much closer.

But try this run a piece of hose from the coolant tank overflow line and put the hose into a bottle, the disco has a 16 or so psi rad cap if you have an engine problem you should be losing coolant via the overflow line.

Lastly check the belt it easy to route it wrong, I did after changing my water pump and I checked twice .

 

Richard thank you for the reply! I have had no less than 20 Disco 2's and every one, I've put a 180 degree thermostat in with great success. However, many moons ago I did actually buy a kit to convert one to in-line and I may just try that tomorrow.

Here's further mystery or confirmation - which ever applies. The top hoses were reading about 105-120 degrees while it was warming up. That bottom hose and the left side of the rad (left side as you look from the front) were only reading 60 degrees! So clearly there is a flow issue.

Here is my plan tomorrow:
1) triple check the routing of the serpentine belt.
2) Drain coolant again and im going to run the garden hose through the radiator from top to bottom to see if there is any flow.
3) If everything seems to be flowing OK, Im going to try the inline thermostat.

Will report back with my results and thank you again!

 

Ok - here are my results form the three steps above in post # 3.

1) Confirmed the routing of the serpentine belt. Had another set of eyes compare from the AB picture on line and all is good.
2) I drained the coolant and ran a garden hose through the top of the rad and water flowed easily through the new radiator. It also flowed through the engine from top to the bottom hose and out.
3) I have a 4th and final 180 thermostat. I decided to boil water in a pot and place that thermostat in. It did open and seem to function properly at 212 degrees F. Note* I did not try to see if it was opening before 212F.
4) I installed that thermostat back in the truck and the same result. Approx 130-140 degrees on the top pipes, and 60 degrees on the bottom out of the rad and up through the bottom of the thermostat. I even had it out for about a 2-mile drive.
5) Finally, I hacked together the inline mod. Took out for a drive and unfortunately, it hit 215 degrees, even hotter than the original design. Same issue that the coolant wasnt flowing - cold rad, hot upper pipes....... BUT..... I decided to start it again after I drove and let it idle. Temps hit 212 again and I heard the aux fan kick in. Then at about 221 degrees suddenly I think the thermostat opened and temps started to go down and the temps in the rad started to level out. Seemed like coolant was flowing properly but only after temps hit pretty high. Any ideas why? Im using the Stant 45358 which I believe is the 180 degree. Perhaps air in the system because without the bleeder T, its definitely now even harder to ensure air is out! (Will pressure fill next time).

I just ordered the Inline kit from Extinct here on this forum so I can get a better fit. I also ordered a FlowKooler Water pump. I will be installing both and hopefully this will resolve the issue.

Will report back on my findings.

 

Did you drill a hole in the Stant thermostat? If not that is why it hit 221 before it opened. You need a bleed hole in it so some coolant will flow past the thermostat and allow the bulb to read the temperature. If no bleed hole, there is no flow and the temperature at the thermostat has to reach 180 by conduction through the coolant filling the hose, so you get 221 at the sensor but only 180 at the thermostat. If you have a 1/8" bleed hole it will open correctly. My thermostats come with a pre-punched hole so no need to drill.

 

Extinct - Perfect -I will wait for your kit which I just ordered a few hours ago. To answer your question, no, I had not drilled it so now your explanation makes sense why it took so long to start the flow process.

Since I have you, do I need any special hoses or am I re-using that top hose from the metal coolant pipe?

 

Re-using top hose.

 

Extinct (and Richard too!)

Got the kit install today and have to say, Im impressed. I opted for the 170 degree thermostat and my truck is finally running in spec now! Seems to run right around 178 cruising down the highway, and at idle and traffic was running about 183-185. Very happy - thank you!

After all the work I put in to pulling the engine and pinning the sleeves, Im confident now this will be an awesome truck build!

Thanks again and highly recommend to anyone seeking cooler temps!