Your Guidance Would Be Greatly Appreciated!

Ok...2003 Disco 2 S 76,000 miles. Bought it 2 months ago..Needle started creeping up to 3/4 about a week ago (in town or at idle) On the Freeway it would go to middle. NOW...Within 10 minutes of driving it goes immediately to high with red light on...Hit the Freeway..it goes to just below 3/4 I turned the heater on and it drops to slightly above middle. HERES THE FREAKY PART.... The heater starts working intermittently...gets real hot then goes to cool...AC works fine. Once on Freeway and needle at middle, I can turn the AC on to LO and needle basically stays in middle......Of course until I get off Freeway..then it shoots to 3/4...Any guidance would be awesome. I just bought a new Thermostat (havent installed it yet), and I want to flush the cooling system, but I'm afraid its a little more than that.... Thanks in advance

 

You need to stop driving it immediately. You may have already damaged the motor continuing to drive it like that. Not trying to scare you, just saying. These are aluminum engines and you can warp the heads or slip a liner from overheating. Do not ever let the gauge get to the red light. As you soon as you see the needle creep up, you need to pull over and turn the heater on.

But yes it's probably something more serious than the thermostat. You need to get it pressure tested. So when it overheated, it seems like it was at lower speeds and the when on the highway that was alleviating it because coolant traveling faster in addition to the extra air coming in. Do you have milky oil?

Check under the air intake near the butterfly valve. That is where the throttle body heater is, you'll see two hoses connected to it. Is it leaking or wet?

My money is on thermostat, headgaskets, or throttle body. Could also be leak, and you are getting air in system causing fluctuations. First things first, pressure test and bleed the air out of the system.

 

Low on coolant, top it off and then keep a eye on it.
You are at the correct mileage for the head gaskets to go bad.

 

X2 on all above , and -

1. Check fan clutch - fan when cold should spin a partial turn when released, feel like peanut butter inside it. When engine warmed up, should still spin, just a partial revolution, not freewheel. If it spins freely, oil inside it is lost and it won't cool truck below freeway speed.

2. Check electric fan - does it run when AC is on ever? Blades should spin freely, and fuse in underhood box should be good. A fuse that blows and/or blades that don't spin indicate a fan motor siezing up, and not enough cooling below freeway speed with AC on.

3. You have a bypass style thermostat, and if you have air in the coolant system (from a leak or worse - exhaust gas from head gasket), heat inside truck wil be on/off as bubbles move around. Coolant is always flowing thru heater core, even with AC on. If you hear gurgles or water rushing, that's a problem. Purge air, top off coolant and bubbles should not keep coming back. Thermostat hoes can get clogged up with coolant system work, and make the stat not work at correct temp.

4. Temp gauge is most inaccurate, if you can get your hands on a scanner or ultra gauge and read temps from OBDII diagnostic port you'll have a better idea of what is going on before temps get out of hand. You may be at 240F or higher. Good idea to change thermostat. There is an 82 C soft spring one that makes truck run about 10F cooler. If you see truck is rising above 220, what is the point letting it go to 240 - 270?

5. If unable to keep cool in center of gauge at freeway speed, in addition to head gaskets, can be low coolant (leaks), bad coolant cap (maintains PSI up to 18 before venting), partial blocked radiator (will show up as cooler on bottom area than top, usually by a lot for than 10F). The rad can be flushed, but usually not effectively, the passages are very small. It is fed horizontally, so should be same temp top to bottom (within 10F on a new one). Sludged up and you don't have enough flow. Rads $150 - $230. $50 at junkyard, but could easily have same sludge, just dried out to a brick.

6. Can be water pump, like impeller blades missing. $3 gasket and a lot of elbow grease to inspect. There are after market pumps with larger bronze impellers.

7. Head gasket will usually put exhaust gas into coolant (bubbles), coolant into cylinder (white smoke), coolant into oil (milkshake), coolant leak external. Before going down that money pit, a $50 exhaust gas in coolant test from parts store might be a good idea.

Murphy's Law comes in a multi-volume set, and you could have more than one problem. In addition to warping heads, killing head gasket, you can also cause a cylinder liner to come loose, and begin tapping when warmed up (no, it did not magically convert to a diesel). Operating at high temps is reserved for life threatening emergency, or guys with heavy checkbooks. To be fair, understand that the gauge is designed to point at the 50% mark until overheating begins. Anything above 50% deserves immediate attention.

And the coolant is a closed system, it had to go somewhere if it is low. Sometimes that is a sneaky leak around a hose connector, of which there are many.

 

Is the check engine light on?
You should have a misfire code eventually.
I went thru all this with my 2001.
And, when you first start off from a light - the gurgling sound.

Of, so if the coolant goes DOWN after you add it
and then you go to the Safeway or somewhere to get food
You come back, open the hood and remove the coolant cap - only to find
coolant bubbling back UP and the level rising..

This is all head gasket pressurization problems of combustion gasses pressuring the
cooling system.

Best to replace the head gaskets and put this problem behind you.
90K to 110K miles probably.
76,000 miles seems (young).
But, if you have had a lot of engine on / off cycles then this may have accelerated
the head gasket wear.

Assuming this Rover is used for many many short trips? Around the block and around town?

Maybe started, trip, sits for 6 hours, then trip, sits 6 hours, trip again.

All the cooling off and then heating up will accelerate Head Gasket wear and eventually failure.

 

How mechanical are you, if not do you have a good Rover shop, not a dealer, near you?

 

Stop driving the thing regardless, it's an aluminum engine, it can/will warp and fail.

 

Stop driving until its figured out...

 

Yup.
Robot says "Danger Will Robinson".
Do not drive that Rover now.
Will FAIL.

Shop = $2,000 to $2,500 down the drain.
Make sure they REDO the heads for this money..

You doing it =
2 weeks of work on and off -
$500 max (maybe).

Would I do heads again?
If I was not working hard at work.
If I had a 2004 that was snappy looking....
I still have all the tools..

 

Here is a picture stream of the work involved.
I did my heads outside in a parking lot in Boulder, CO.

There is an indy shop in Boulder called Araphoe Imports.
They will do heads gaskets for $2,000 or so and even put on re manufactured heads.