Diagnosing overheat on D2

[kcabpilot]

I know this has been discussed ad-infinitum for years and I have researched and read much on the subject over the past few days. I recently did a 2700 mile excursion to Utah that included the Burr and White Rim trails in and around Canyonlands and Moab as well as some other fairly demanding stuff. The Disco performed stunningly well and took everything I threw at it but on the way home I got an overheat light as I started across Nevada in Caliente. I got some coolant at the auto parts store and topped off the system. Everything seemed normal and I could see no leaks. At idle and driving around town the temp was stable at around 193 F. On the highway all was okay until I hit the first grade at which point the temp began a steady climb. I decided to try get back to my brother's place in Cedar City and was able to do so but had to stop a few times to get over Panaca Pass. I had to shut down twice for half an hour to let it cool, I later discovered that by just letting it idle it would cool down quicker.

Anyway, when I got back I came to the conclusion that my viscous fan wasn't working, I couldn't hear it running and upon shutdown it didn't seem to have any resistance so I got a replacement at Autozone. Upon first start I could immediately hear the fan and all seemed fine, I thought I had fixed it. I went into town, filled up, drove around doing some other errands and when I started up the hill to my brother's place the temp began to climb again. I thought maybe I had gotten a defective fan (it was only fifty bucks) so I took the fan off of my brother's '04 but still no luck.

I had only three days left on my vacation so I flew home and drove my truck 611 miles back out to Utah where I rented a U-Haul trailer and brought the Disco back to California. As before I can start it and idle all day long and the temp never goes over 195. I should add that the electric fan is working as well although it does not come on at that temperature.

So I'm trying to develop a plan for troubleshooting this. Could it be a bad thermostat? Could it be a head gasket? Is there anything else anyone can think of or a test plan I could follow to diagnose this? The engine starts up fine, no misfires or any other indications of a problem. It just won't go up a hill.

 

[Shiftonthefly1]

When you topped off the coolant...where did it go? Have you tried bleeding the system? Is it possible that your radiator has deposits in the bottom? I don't see your milage and you didn't mention having replaced it at any time. Are you running factory temp T-stat?

 

[kcabpilot]

Mileage is 141k, original radiator, standard OEM thermostat. Coolant loss I assume was through vent when it overheated. I don't lose any coolant driving around on the flats. I suppose I should have the radiator looked at by a shop. Thing is this came on suddenly rather than building up or showing any symptoms. When I added coolant I topped off through the bleed port at the T so system should be free of air.

 

[number9]

New reservoir cap may be in order to try.
......

 

[adriatic04]

are the tubes getting hard from pressure when its hot? You can shoot an IR gun at the radiator and see if you are getting temp difference. The 180 tstat allows everything to open much sooner and allow the radiator to breathe a little easier, I would try that for one.

 

[kcabpilot]

Yes the hoses were hard when the coolant got to the boiling point which, by my estimate with 50/50 mix and the standard 20 lb pressure cap should be somewhere around 260 F. I've been studying the manual chapter on the cooling system and also have read up a bit on viscous fan clutches. I don't think there was anything wrong with my fan clutch but, understanding a bit more about them now I believe there were some symptoms leading up to this event. One of them was that I could hear the fan engaging on and off as I was cruising down the highway and this is not normal. The engine driven fans purpose is to provide air flow at low speeds or when not moving. At cruise the airflow across the radiator from your motion should be sufficient.

Being back at work following my vacation is sucking up all my time but this weekend I'm going to do a few things. I'm going to pull the radiator and have a shop flush it and check it for flow restrictions. I'll also test the thermostat and get a new one if necessary. I will also pull and examine all of the spark plugs to check for any suspiciously clean ones that would indicate a head gasket problem.

One way or another I'll get to the bottom of this. I need my Disco back!

 

[adriatic04]

tstat is fairly inexpensive and if its never been changed I would do that and see if it helps flow.

the electric fan WILL come on if your radiator temps hit 212 (D2) even if you are moving. It will turn off at 50 MPH or higher AND 82 ambient temp, but again, if your coolant temp gets high because of a stuck or poorly flowing tstat, then it will come back on and aid in cooling.

i dont think fan or clutch is your issue, I think flow from rad or tstat is your issue in poor cooling

 

[kcabpilot]

I agree, both electric and engine driven fans seem to be working as they should. Thermostat was changed about 5 years ago but radiator is original and has never been serviced in any way

 

[Shiftonthefly1]

New radiator is like 100-150 on ebay. Doesn't seem worth testing get or flushing when a new one is so cheap.

 

[kcabpilot]

Thanks I'll look into that. To be honest I don't know if a radiator shop can do much with plastic headed radiators anyway. My concern is that although there seem to have been warning signs this condition came on suddenly as if something failed. I was not monitoring my temp with the scanner prior to the event but did notice afterwards that the instrument gauge needle does not move above the center point until the temp hits about 230. So based on hearing the fan at cruise I suspect it had been running hot without me really noticing it. Once the overheat light came on the situation deteriorated and now it definitely will not climb a hill without overheating. So I'm hoping I didn't blow a head gasket but even if so I'm prepared to deal with it if necessary.

 

[jymmiejamz]

Radiator would be my bet too, but I would also throw a thermostat in there at the same time. If you cut the radiator in half you will likely find the bottom half totally clogged.

 

[kcabpilot]

Pulled the thermostat today and it seems to be working okay but hard to tell for certain. If I pour hot water from my electric tea kettle, which is 195 F, it appears to open maybe half way based on my counting the seconds for it to drain through. When I boil the water to 212 F it seemed to open all the way. The bypass spring also seems to work okay.

I have a new thermostat coming as well as a radiator and a new cap for the expansion tank. I figure that even if it turns out I do have a head gasket problem it's probably due to the overheat rather than the initial cause so I will want a new radiator anyway. I looked at the plugs and did not see anything abnormal. I'll install the new radiator and thermostat and see what happens.

 

[jymmiejamz]

Radiators are a wear item that are a slow fade. Even if it doesn't fix your problem, it is something that will need to be replaced at some point anyway.

 

[kcabpilot]

Update: I've got a new radiator, thermostat and pressure cap. Old stuff already removed and honestly did not find any smoking gun, radiator seems clean and unrestricted, new thermostat acts pretty much like the old one when testing with hot water. So I've also got a block tester kit. My plan is to put it all back together and fill with distilled water, run it and see behaves. If it still overheats and fails the test I'll try to isolate between banks and possibly cylinders then pull the heads and do a pressure test on the bare block.

Now, I'm getting a little ahead of things here but if it turns out to be the block I want to know what options I have. Atlantic British has short and long blocks for a not totally unreasonable price but shipping (two ways due to core return) all the way across the country might be a deal breaker. I'm wondering if there is a better source on west coast for a tophat liner block or a document that a good machine shop could use to modify my block after repair. I'd also be interested in possible performance enhancements such as cam or crank substitutions that could up the output of the 4.0 or if it's even possible to drop a 4.6 into a 2001 without a lot of headaches.

Whatever it takes I'm committed to getting my beloved Disco back on the road and trail. Any advice/help is welcome.

 

[listerdiesel]

Just a thought, have you thought about checking the air bleed pipe from the driver's side of the radiator top and the bleed needle in the header tank that it runs to?

I had a piece of limescale in mine that blocked off the air escape and it did make a difference.

Our radiator is original 1998 build and runs on 50/50 OAT with no problems, 2000 miles in France last year with the big trailer with no problems in mid summer heat.

Peter

 

[kcabpilot]

I'll check that out Peter.

One small ray of hope: when I pulled the temp sensor out of the old radiator it was encrusted with a thick layer of scale which I assume the entire inside of the old radiator must also be crusted over with which would seriously degrade it's performance capability to transfer heat. I'm keeping my fingers crossed, up until now this has been such a good engine that has never leaked nor used so much as a drop of oil between changes.

 

[listerdiesel]

Shouldn't be any scale in there if the correct OAT coolant is used.

Peter

 

[kcabpilot]

I ditched the OAT about 5 years ago. There has always been a lot of controversy over this topic and there were plenty of stories about the orange stuff creating problems. In my opinion OAT is simply about the environment and not anything special about the mechanicals. In the Disco it did present some problems because of the complex system with so many connections that is prone to leaks, especially the infamous throttle body heater circuit. In my experience, any time there was a leak or air somehow got into the system the OAT coolant would form a crusty, corrosive looking residue. So I did some research and found a lot of horror stories about the stuff clogging up radiators and other cooling system components. Maybe it's not all true, we are dealing with the internet here after all but nonetheless I switched to glycol and it hasn't been a problem.

As for the scale I found on my temp sensor, it's not the normal kind. It's soft and crumbly and dark colored but this is a different topic. Right now I just want to get my truck fixed.

 

[jymmiejamz]

If I had a DII the first thing I would do would be switch to green coolant.

 

[riceybean]

Any coolant in the oil? Slight white residue on the filler cap? I THOUGHT my leak was a head gasket, turned out it was a front cover leak( I removed the heads before I found it). It was a massive one so really not related but the P.O. did state that it was loosing coolant.. someplace. He could never find the source until it blew out completely. I wrongly diagnosed it as the heads. Live and learn.