This is making me a bit nuts so I'm tossing it out there to see if I need to fix it or flee..
Here is the history....97 disco, 165K, problem is over heating.
What has been tried: corrected belt routing (Thanks Spike) that seemed to fix the problem (I think Spike's comment was "that was too easy" and he was right).
Truck runs nice and the temp gauge reads dead horizontal sometimes for 100 miles other times 4 miles and boom it shoots to the top of the gauge. It's the inconsistency that is making me nuts. I replaced the t-stat and again everything was groovy for a 100 mile trip and boom. I removed the t-state today and drove 20 miles everything is peachy and boom it spikes again. I checked the plate under the throttle body and no sign of a leak. I've bled the system several times. The fan is locked in full motion so I assume...this is not the problem. So I'm thinking radiator? Water pump was replaced a ways back.
I don't get way it would run great for a respectable distance and then overheat.
Maybe it's just part of the fun of LR ownership?
Thanks in advance for hints and wisdom!

 

Could be a bad radiator, thats easy enough to check.
Once it starts to overheat pull over and shut it off and feel the radiator all over, should be cooler at the bottom but not cold.
Next thing to check would be for exhaust in the coolant, you need a test kit for that.
Autoparts store how those kits.

 

I'll try the radiator temp touch method. I'm guessing that if it full of sludge and gravity still applies it will be less effective at the bottom? I need to take one apart at some point.
Thanks.

 

It is supposed to be cooler at the bottom, but what you are looking for are "cold spots", if there are parts of the radiator and that way colder than others you have a blockage.
You can also use a infrared thermometer.

 

1. Overheating quickly, while at roadway speed, could be a sticking thermostat. Replace it. Would be erratic. Now you ran it without a stat, but that does not allow water to stay in radiator long enough to cool off properly. The stat could have been part of the problem, and removing it changes the frequency at which the problem repeats.

2. Dead horizontal - if that means the temp guage, on a Disco 1, then that means close to overheated to start with. Norm seems to be in the bottom 1/3. When using a scanner that reads live data, you will find that the lower reading does not change much from 135 to 220 degrees. So if you are running horizontal, and at highway speed, then the obstructed (leaves, mud, etc. on outside or crud/calcium on the inside) radiator could be the issue. My indy rad shop told me a good radiator is within 10 degrees across the surface. Cheap to have "acid boiled" and rodded out ($65 in my case).

A scanner would be a good thing to use now, because you could be chasing a bad temp sensor, the guage one is the single wire (which could get a skinned place grounded and cause the rapid meter rise), the ECU one is the two wire. Guage could read far different from scanner. If no scanner available, how about an infrared point and shoot thermometer? Something to give you real data at the same spot, other than the guage.

3. If you have combustion gas in the coolant the chemical test will show up. Many have said that the upper hose can also become rock hard, the coolant cap can vent, etc., to go along with head gasket symtoms. The 1/2 inch pipe thread on the radiator top plug would allow a pressure guage to be mounted for analysis.

4. Maybe water pump is not doing so good. Might be worth a gasket to get an inside look. If you did not DIY the pump change here is an inside photo of one your age and a newer one. Maybe impeller is loose on shaft.

5. What you describe seems to most likely indicate a water flow problem, as opposed to air flow. Your problem does not build up slow and steady, it "pops" up. A restricted radiator could be part of the problem, but it is hard to image it on/off like a switch. And radiator / fan problems should also show up at idle or slow traffic. Gurgle noises under the dash are many times present with HG problems, you did not mention that.

6. If you are not the original owner there could be other issues. My PO had replaced the electric condenser fans behind the grille and wired them backwards. So with AC on, those fans blew out the front, and the main fan blew out the back, and at certain rpm there was almost no cooling. But at highway speed it was OK. Test is turn on AC without truck cranked, feel air - should be going out the back. Main fan on vicous clutch - curved side of blades should go toward engine. Fan clutch is designed to turn with less power at normal temp, and increase power when hot. If air flow from radiator is blocked in areas this could be erratic. Main point is that air should NOT be blowing out the grille. You can run the truck at high way speed with no fan, just don't stop or idle for longer times.

7. Hopefully there is not a plastic trash bag sucked up in the space between the radiator and the condenser, or lots of other trash. Should be able to shine light through the fins of radiators, might need to blow or wash out.

8. AC compressor could be getting very high head pressure, which would dump more heat to condenser. My compressor was actually tripping out due to the high pressure limit switch. You did not say if AC off makes a diffeence.

9. Radiator shares an engine oil cooler and a transmission oil cooler. And no mixing of any of the three is allowed. Trash in cooling system obstructing pump, or flow around sensor?

10. If you verify that the guage is reading correctly, and you are really having these spikes, I don't see how you could operate the truck safely with respect to HG or warping heads until repairs are made. "Water wetter" additive for coolant might help while working through it.

 

My bad. I have the gurgle under the dash. Should have mentioned that. Like all other symptoms it is intermittent. Thanks for the responses.

 

You can have a gurgle for just air, or it can be HG related. But the rapid change, where it starts from, and how high it goes would worry me. Seems like a bad HG would not wait until after 100 miles to show up... but you might be at normal air flow/water flow for 100 miles, get off the freeway, and cooling system can't handle the change due to marginal radiator. I include pix of my temp guage and scanner for reference, here we are at 207 degrees and not yet close to horizontal.

I suspect you don't have a single step problem, but a chili-cheese-slaw dog-with pickles on the side...

 

Thanks for the insight. I'll go to work on it and report back if I actually id the problem(s).

 

If you have air in the cooling system it will cause the truck to overheat, air cant cool the engine.
If the air pocket gets stuck at the temp sensor probe the truck will overheat according to the gauge.
You need to get the air out.

 

I am now worried. My rover is always horizontal. Summer or winter. However when the a.c is on I go up above horizontal. From 0 maybe 2/3 the way up. I have a new fan clutch and I did a flush on the radiator last fall. I think I have a air pocket because I had a head job 2 years ago. I have the waterfall in the dash sound the first time you step on the gas in the morning but never anything after. I also replaced my fan clutch this year. I have no idea about the thermostat, when I get back home I will check it out.I know for a fact I have NO air blockages.
thanks