Good evening everyone,

First post here, though I've been doing a lot of reading. Hoping to get some input!

Finally converted over to a Disco 2 after many years of wanting one. Need a family wheeler that can handle more than a Jeep WJ or XJ.

Picked up a clean rust free CA model with 122k on it. Really clean find for MI.

Changed fluids, idler bearings, etc etc. PO changed water pump due to "no heat", flushed system, etc etc. Has green coolant.

Decided to throw my scanner on it and check things out, to my surprise, it was idling at 210-215 F. Went for a drive, saw a spike to 221, and mostly cruising temps of 208-210. Never got higher than that. Started poking around with the IR thermometer. Ambient temps are anywhere from 35-60 F.

Top Rad hose - 175

Top of plenum by sensor - 215-220 at one small spot, rest is 190-205

Metal heater core inlet line - 215-220

Metal heater core outlet line - 200 ish

Thermostat housing top - 155 ish

Thermostat housing bottom - 130 ish

Lower Rad hose - 100ish

Rad inlet area - 170-180

Rest of rad - 100-140

Drew the somewhat logical conclusion that I may have a stuck thermostat since very little fluid is moving through the bottom. Top and engine side rad hoses are normal firmness, and I have heat in the heater core, so its appears to be moving fluid. Ordered a 180 thermostat, clamped off the hoses, put it in, quickly bled the system via the methods on this forum, and proceeded to drive it all this week, roughly 16 miles each way to work.


Top Rad hose to the thermostat and radiator - 165 on all parts of the tee

Top of plenum by sensor - 205-215 at one small spot, rest is 180-195

Metal heater core inlet line - 205-212

Metal heater core outlet line - 187

Thermostat housing top - 145

Thermostat housing bottom - 135

Lower Rad hose - 100ish

Rad inlet area - 160-170

Rest of rad - 100-140

Metal outlet tube from the block to the top radiator hose - 165

Water pump surface - 150-165

External cylinder head surface temperatures - 220-240 - pretty normal for surface temps, especially by the exhaust.

Mechanical fan is moving a LOT of air when warm. Clutch feels good.

Engine heats up normally, pretty quick under idle or driving conditions. Then just sits at 195-199 while driving, and 201-205 while idling. I can let it sit there and idle for 20-25 minutes and it doesn't move. It appears as if the radiator slowly, slowly, slowly heats up. Almost as if the fan is pulling too much air and the engine can't quite generate enough heat to heat the thermal mass of the engine+ radiator.

Couple theories:

1st - plugged radiator (checking tomorrow when its light out). This would account for the low outlet temperature. However, PO had it flushed (supposedly) and the heat gradient across the rad doesn't scream plugged radiator to me. More screams "not getting hot enough fluid, and the fan is pulling plenty of cold air to cool me"


2nd - air bubble trapped right at the coolant temp sensor, and apparently in the tube running to the heater core? I'm leaning this way because the temperatures I'm recording everywhere else lead me to believe that the thermostat is NOT getting hot enough to open. Accounting for the gradient of temperature across a rubber hose with a hotter fluid running through it, it appears as if the fluid leaving the engine is not sufficiently hot to open the thermostat enough. Obviously some is getting through the radiator because the parts of the rad outside the diameter of the mechanical fan, and the lower hose are SLOWLY warming up. Even the outlet tube AT THE ENGINE to feed the thermostat/upper rad hose is only 165 ish degrees. I know IR temps can be deceiving while reading rubber/plastic, especially with a moving fluid, but even account for the drop in temp, it still does not make sense.

3rd - Combustion gases? Its not building excessive pressure. I'm testing for combustion gasses tomorrow as well.


So at this point I'm thoroughly perplexed. I've designed, fabricated, and raced high end race vehicles for years. Desert, short course, rally. I have a master's degree in mechanical engineering, and I'm an engineering professor. I like to think I have broken enough stuff, and screwed up enough to have a decent idea of how most things work. This one though, has me perplexed. Initial diagnosis on my part was head gasket/cracked block/head/liner, slipped liner, plugged radiator, etc. But the data doesn't seem to fully support the idea that it is truly fully overheating. Its almost like the rad is cooling TOO much and injecting cold water into the thermostat housing and not letting the thermostat open enough. I'm wondering if I went for a longer drive than 25 minutes, if it would finally bring the radiator up to temp.

So to recap, the feed line to the heater core appears hot, as does the return line (definitely exchanging heat because I have heat in the cab, and the temperature drops in the return line). Immediate sensor vicinity appears hot, with one spot seeming to match the readings. Yet the external lines feeding the thermostat, etc don't appear warm enough to open the thermostat all the way. Yet obviously it is, because cruising temps and idle temps stay between 195-204. No obvious sound of trapped air.

Open to suggestions. If it were truly overheating, and the radiator, lower line were cool, I'd diagnose as plugged radiator. But something doesn't line up. In these ambient temps 35-60 F, does anyone else's radiator/thermostat not fully open? I've never had a vehicle that would....

Thanks in advance!

-----------------------------------------------------------------------------------------------

Chris

Founder: 13Motorsports Race Apparel
Owner / Driver: 13Motorsports Racing Pro UTV #13 / Ultra4 #131

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Professor of Engineering - Northwestern Michigan College
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Temp between 195-199 as you stated seems ok for D2, & idle at max 205 is still ok,
Bypass thermostat in these engines have a little more trouble than inline stat to open up at cooler ambiant temp's , 30-60* outside temp, cools radiator so much that as coolant passes the lower part of stat to go back to engine closes the thermostat, these engines are known to not cool of as much as inline stat engines in colder climates,
They say it's to get engine warmed up quick in cold climates, but in reality it's a poor design & they used it to control the flow is cold coolant to aluminum block with steel liners, to avoid sudden changes it block temp, (since aluminum & steel expand & shrink in diff rates),

 

From the readings you're getting from the heater hoses, it seems like you should have good heat. I would check the blend door actuators and make sure they're opening and closing properly.

 

That is the same mindset I have at this point. Radiator/mech fan is overcooling the coolant and not letting the thermostat open any significant amount. Engine just isn't putting out enough heat in my 30 minute drives. Maybe go for a longer run?

What is puzzling to my engineering mind is the hot spot by the sensor housing and feed line to the heater core. I'll rebleed the system I suppose. I'm really considering swapping to an inline system. Not sure this bypass system will work with the future plans of throwing my spare Dana 60's and 37's under it.

Thanks for the reply! I believe you may have misread the issue though. I have plenty of heat fortunately. Issue is that while the sensor and immediate heater line is at 195-205, the rest of the cooling system is significantly colder, and thus the thermostat is not opening.

 

If you have installed a genuine TD5 180* stat you should be fine (if rest of cooling system in perfect order), but yes, an inline set up is ultimately the best to keep system more consistent,

 

I would flush it again and make sure your coolant mix is correct. Green is o.k. In my opinion
Take your time bleeding the system and follow ALL the recommended steps.
Make sure you bleed it completely cooled off. Make sure the resivor is as high as you can get it.
If you are not getting good heat, it's not bled yet
My 2002 runs 180 -190 all day long in all temperatures with a 180 stat
Read my thread titled "running hotish"
Very similar
Good luck

 

Thanks for the reply! However I think you may have misread my apparent problem. I have plenty of heat. Works great. My apparent issue has to do with it running at roughly normal temps, but does not appear to actually get hot enough to open the thermostat at the thermostat housing.

Bled again today. Went for a short drive and let it idle for 20 minutes. Temp read 203, yet the hoses and thermostat housing never got over 160-170 based on IR thermometer. Radiator never really got over 100. Ambient temperature was 34.

It seems like the mechanical fan is moving so much cold air that the engine can't produce enough heat to bring the entire thermal mass of the engine-side coolant up to temperature and open the thermostat. The injection of cool fluid from the bottom of the radiator keeps the thermostat closed unless I load it really high

yhaQUOTE=Discoaddictnorth;543941]I would flush it again and make sure your coolant mix is correct. Green is o.k. In my opinion
Take your time bleeding the system and follow ALL the recommended steps.
Make sure you bleed it completely cooled off. Make sure the resivor is as high as you can get it.
If you are not getting good heat, it's not bled yet
My 2002 runs 180 -190 all day long in all temperatures with a 180 stat
Read my thread titled "running hotish"
Very similar
Good luck[/QUOTE]

 

I don't have an infrared thermometer but I started having a similar issue when ambient air temps lowered. I put a 180 tsat, new hoses, fan, clutch, tank, cap, water pump and fluid flush at summer time. Temps were at 200 after everything which was lowered from the 217 degrees it was running at when I bought it. Added water wetter and got it down to 194 idle, 198 highway. But NOW it will idle to 194 and hit 198 on the highway but soon as I hit traffic and come to a stop or exit off onto the city blocks, temp will continue to increase as high as 203-205. My engine hasn't hit 200 in months. When it gets above 200 I will turn the heater on and it drops 5 degrees. I was going to get another Tstat or make sure mine doesnt have something stuck in it, just not looking forward to air bleed and such. That can be aggrevating

 

Thanks for the reply! I believe you may have misread the issue though. I have plenty of heat fortunately. Issue is that while the sensor and immediate heater line is at 195-205, the rest of the cooling system is significantly colder, and thus the thermostat is not opening.[/QUOTE]

Oh okay, I see what you're saying. I think the only way you can really tell what the thermostat is doing, is to remove it from the vehicle. Then you can heat up some water on the stove and monitor the water temp with a thermometer and watch it. The thermostat should begin to open when it starts to heat up and should fully open when it gets to the regulated temp. So if you're running a 180 degree thermostat, it should be fully open right around that temp. This is where Land Rover thermostats are a bit of a pain! They're all enclosed in the housing so it's hard to see exactly what it's doing, but it should be noticeable when it opens. I think I've checked mine like this before. It was okay, but the truck was overheating due to a bad head gasket.
I'm assuming your thermostat is doing something because if it was stuck closed it would most likely cause overheating unless the coolant is bypassing around the thermostat somehow.

 

I kept an eye on it again today. crank and idle the temp maxes out at 194. This is on a 50 degree morning, highway temp is 194 at a constant 65 mph. Exit off of the highway and stop for access to 2-lane FM road. Temps creep up a few degrees, immediately. Now I take off at 198, temps come back down to 196 for the 1-mile. Now I stop and turn into the driveway and park in the garage. Temp shoots up to 201. It didn't do this during the warmer months.