This is driving me crazy, and I'm hoping that you guys can give me some ideas. I appoligize in advance for the lengthy post, but I will try to give you a good picture of what is going on...

My 2000 D2 seems to be running a fever....

When I am going down the road (60-65 MPH) the engine temp seems to run around 203-208. However, if I slow down (40 MPH), it will heat up to the 210-215 range. I can ride down the road for miles and the temp will stay in this range. I have noticed several things:

-When I let it sit and idle (lower thermal load), the temp will get to 212 or so and the fan will come on and very slowly lower the temp back down to 204.
- If I am driving at the slower speeds (40MPH), I can shift from D to 3 to bump up the RPMs and the temp will quickly begin to fall to 203-206 ish.
- If its 75-80 outside, its fine (204-208) as long as I'm going highway speeds, but if I slow down, it will get to 215 even if its only 40 outside.
- I can turn the heat on and the temp will slowly return to the 203-206 range.

It has not run hot, but it worries me as it does seem to have gotten a little worse lately. It previously would hit the 210-212 range, but just started routinely hitting and holding 215 this week.

I have flushed the system, replaced the fan clutch, just installed a new radiator, and installed a new thermostat not too long ago.

I use an ultraguage to get the temps above. I checked temps with an infrared thermometer and I seem to be getting a good temp drop across the rad (I think it was 50 or 60 deg, cant remember exactly)

I am thinking it might be the water pump not being able to supply adequate coolant flow at low RPMs. This would explain the quick drop when I downshift. Any thoughts that you guys have would be greatly appreciated.

Thanks

 

1. I share your concern that things are too warm. The stock stat (and I don't know of any alternate values for a D2 in line 3 legged stat) is fully open at 204 F. So one would think that with coolant system in top shape at freeway speeds we would see something just below that at times.

2. Your electric fan is working as designed, on at 212, cool engine down, off at 202 (below max open point for stat). Your is a liitle above that but close.

3. You have done many of the things that might be gremlins. Let us look at what is left:

A. Water pump - good operation is from firm fitting serpantine belt, correct route, no wobble. Pix of worn water pump. There is an aftermarket pump available in the $150 range from British PAcific I believe that has a larger bronze impeller. You can also remove and inspect pump for a $3 gasket.

B. System not full of coolant - line below coolant bottle twisted.

C. Heater core not blocked, but partly restricted. When main stat is closed, sample of hot coolant flows thru engine to outlet pipe, down the top of the stat through those four holes, and mixes with coolant from radiator to get thermostat to open. How fast this is taking place could be impacted by the parallel paths of coolant circulating thru heater core, and the very minor issue of coolant circulating through throttle body heater. This could be tested by using some hose splice (male to male) kit from the blister pack aisle in auto parts store to remove heater from the circuit for testing. Flush heater core with garden hose.

D. There have been reported runs of defective stats, this seems to be more "fail to open".

E. The ECT could be inaccuarte. Fairly cheap coolant sensor. Could be home tested by removing from cold or warm, but not hot engine. Leave plugged in to harness. Put in coffee cup of hot water from teapot, measured by another thermometer. Compare readings to scan gauge for coolant temp.

F. Fan blades might have been reversed on something - the cupped side goes toward the engine block.

 

Thanks for the quick reply. I think I can eliminate a few of these options:

B. The cooling system is completely full and the lines are not twisted. (and has been bled)

C. When I flushed the cooling system, I pulled the heater hoses and made sure to thoroughly flush the heater core. There was ample flow with no back pressure.

E. I feel like the ECT is at least close to accurate. When my gauge was reading 206.6 I put the infrared thermometer on the metal section of pipe that feeds the heater core and it read 205. So, that leads me to believe it really is running warm.

F. The fan is installed correctly so as to pull air through the radiator towards the engine as designed.

Of the options you listed, that only leaves the water pump and thermostat. I feel like the thermostat is probably ok. I forgot to mention earlier that if I drive on the interstate (75-80 MPH), the temp will actually go below the full opening temp of the thermostat. Under those conditions, it tends to run anywhere from 194-201. But, the engine is turning over 2500 RPMs at that speed. Of course, I guess that doesn't totally eliminate the possibility of the thermostat not functioning properly.

So, given that info, do you guys think I'm on the right track as far as the water pump?

 

Disco IIs run too hot IMO. My RR stays at 195F at idle... The 03 I have will go to 215F at idle (this was during summer). I replaced the t-stat (pita) and the Disco now idles at 199 to 201F (It is freezing cold here right now though) which I'm comfortable with. However, when summer hits, I'll be using an aftermarket t-stat to keep her cooler. The T-stat on my RR is designed to open fully at 180F. I don't know what LR was thinking when they made the Disco II and decided to use a t-stat that opens fully at 204F. IMO Disco IIs had so many head gasket/block problems because;
1. they used dexcool
2. they have inaccurate temp gauges (was in one that was reading 240F and the instrument gauge didn't budge) so by the time you figure out it is overheating, its too late.
3. They are designed to run warmer than most cars.

My Jag's V8 runs at 185F... The same engine is used in LR3s and newer RRs.

 

Agree on need to re-pump. Here's why:

1. The D2 is at a disadvantage because the thermostat is some distance from the sensor that indicates engine temp. So if you put identical stats in a D1 and D2, the engine temp would be different.

2. Here's some info from Stant, a good sized producers of stats:

The thermostat starts to open at the rated temperature, plus or minus 2 degrees (F).

The thermostat is usually fully opened at 15 - 20 degrees (F) above the opening temperature

So an American parts store that sells you a "stat for your vehicle" will sell you a 195 F. And it will be fully open at 210 - 215 F.

Now from the RAVE for a D2:

warm-up. The thermostat is closed at temperatures below approximately 82°C (179°F). When the coolant
temperature reaches approximately 82°C the thermostat starts to open and is fully open at approximately 96°C (204°F). In this condition the full flow of coolant is directed through the radiator. The thermostat is exposed to 90% hot coolant from the engine on one side and 10% cold coolant returning from the
radiator bottom hose on the other side. Hot coolant from the engine passes from the by-pass pipe through four sensing holes in the flow valve into a tube

surrounding 90% of the thermostat sensitive area. Cold coolant returning from the engine, cooled by the radiator,

conducts through 10% of the sensitive area. In cold ambient temperatures, the engine temperature is raised by approximately 10

Now the available choices for D2 stat with stock plumbing layout are sorta restricted.

So if you are running down the road, with about same size engine block, and can't keep temp near opening temp of stat... that's when questions start. And if you can't keep temp even close to wide open value of stat, then has the closed loop system of cooling exceeded the capacity of the stat?

But enough pondering the great mystery.

A D2 owner would be wise to replace a water pump also in the OP original situation. The pump needs to circulate enough coolant through those sample holes in the stat to warm up the stat valve and open. So a weak (erroded impeller, slipping impeller, scale covered impeller) output water pump would do less of a job at this, and engine heat would rise. Disco Mike found a pump with a bronze impeller, which will have a higher flow rate. I may have mis-spoke in other posts, the vendor is BP - Utah. Pix attached. Also pix of old/newish regular pump, and closeup of scale encrusted wobble pump impeller. Note brown coating in old pump from "stopz leekz", which coats the entire inside of the cooling system, reducing heat transfer, like wearing a sweater in the summer.

There have been posts on the internet of owners modifying the thermostat by breaking out some of the guts, to achieve a "no stat" condition for emergency repairs. If I had one, I would be tempted to use a drill bit to enlarge the four sampling holes in the "top" opening, so that more hot coolant would reach the stat sooner. I would hope this could reduce the time lag for opening.

There are also write ups of re-plumbing and installing a conventional stat (180 F) in the hose. Would think it not needed if everything else is up to snuff.

 

I can't help much here, but going through the same thing on mine, although my temps are even a bit higher.
Buzz, I was looking for the new sensor last night and came across this, which I did not come across while doing the repairs. Also, gets me back to thinking about those items from the RAVE talking about a higher engine temps when cold, etc. I figured something like this can fit in what was a drain plug hole in the bottom maybe. I was not sure if my truck had this stock or not, being the radiator was not original when I bought it.
Sensor Engine Temperature D2 W / Air Injection for Discovery Series II available at Roverparts.com

 

Also, I keep wondering if this is something different from the stat and might be an issue on mine:








engine rev/min

 

For both of you guys, if you want some help, send me your number and I'll be glad to walk you thru what to check.

 

Well, there is a stat on a D2 radiator that is supposed to supervise temp, be compared by ECU, and set a code if main stat is stuck. Little late at that point....

Here are the codes for it:



coolant temperatures too small

RAVE pages attached.

Since the coolant thermostat is some distance from the actual block opening, I would wonder how much the coolant heat is dropped by air flow over that rubber hose and metal outet pipe. Could putting some form of pipe wrap (with zip ties, so it will stay put) over the coolant outlet pipe and the rubber T hose over to the actual thermostat make it work better? Normally in that path, you would have a small trickle of water when the stat is closed. That trickle goes thru the metering holes on the top of stat and mixes with cold water from the lower hose, and when it warms up the stat enough it opens and we have good flow. Then the process starts again, either fully closed or open to some degree. You want the stat to be responsive, not lag behind engine temp changes. So maybe a passive fix would increase the temp of the sampled water, and let the stat work earlier rather than later.

Maybe the size of those metering holes has changed by various factories. Or just a bad stat.

A puzzle to my weak mind, my 4 liter power D1 makes it down the highway at opening temp of stat + 2 degrees. Many D2 owners report running at 30 degrees above opening temp of their stat (based on 180 opening temp). That's quite a difference for what in some cases is the same short block.

Of course, this is exactly what Rover did not want to happen, people looking at short term changes in numbers and becoming nervous, going to service departmnets, etc. So on the D2, the ECT drives the ECU, which computes a range of temps for the gauge to be driven at 9:00 by digital pulse width modulation. An analog looking gauge, which is really a digital indicator light.

 

Ok, so any idea where that sensor is? I replaced the entire cooling system and did not see it. I think mine is a pressure issue where maybe the stat just is not opening unless the rpm is up there. Sounds like maybe the same with him. If that is the stats job, will be easy. If elsewhere, I don't know.
I drove it to the airport today on the highway. Cold temps out and stayed 208 or so. In slow traffic it was 225, but I would shift down a gear and it would instantly go back down, which is telling me pressure or flow. Being the water pump is new and system is totally clean and flushed, pressure could be key in not opening the Valve mentioned in rave.
Imaging to buy the oem stat from AB and see where things go from there. The ect sensor seems accurate with a couple tests so I don't thi k that is it.
Mike, when I'm back in town this weekend I will throw in the new stat and see where we go from there.
Also, no codes.