Hi guys.... I need to start out by saying that I am a complete noob to all this stuff and know very little about cars in general, so I apologize in advance for my ignorance.

I was given a 1997 Land Rover Discovery while I was on vacation in Vermont. The vehicle just (the day before) had its engine replaced by a mechanic who gave everything the green light. My wife and I drove the car around town without incident, however, on our 4 hour (on the highway) trip home, the car overheated. We discovered that it only overheated when the heater was not on. If I left the heat on, the temp gauge did not go over the halfway mark and stayed steady for the entire trip, but with the heat off, the temp creeped up.

Since getting the vehicle home, my friends (more mechanically inclined than I) have taken a look at the vehicle and made a wide variety of assumptions as to what is wrong with it.... air pockets, blocked radiator, thermostat, water pump etc... They noticed that the top hose did not seem to have much pressure and that both top and bottom hoses were hot. Also the car can idle indefinitely, without the heater on, and not overheat.

Finally I called the mechanic that put the engine in. He believed it to be an air pocket and told me to loosen the radiator reservoir cap and drive it for a while with the heater on and let it get up to temp. He than said for me to let it cool overnight and then, while cool, top off the coolant and then repeat this process, which I did. (note: I may have overfilled a bit) While I was doing this, the car did not overheat... even if I turned the heater off. However, the second time I did it, when I came to a stop, the car shot out a significant amount of coolant through the overflow cap (which was loosened). My mechanic though this may have been the last air pocket escaping and told me to top off the reservoir one more time and this time tighten down the cap. I just took the vehicle out for a test drive and it overheated with the heater turned off.... it was absolutely fine with the heater on.

Sorry for such a long description... does anyone know what this might be? Could it still be an air bubble? Should I flush my radiator? My friend is pretty sure it is my water pump... is there any merit to that? Help!

 

The heater is acting like an aux rad. Picture a small radiator installed under your dash. Coolant circulates through this small radiator (heater core) and a fan blows air across it to heat your cabin. So operating the heater may be just enough to keep the engine cool but is hardly a fix for your problem as that just means you are on the edge of overheating at any time.

There are a myriad of things to check and it sounds like you are in the process of narrowing things down now. generally when a vehicle runs hot at highway speed it's an indication of radiator blockage. That can be something as simple as leaves and debris in front of the rad to internal corrosion and blockage.

You will get a variety of opinions and advice on this problem but one thing is for certain...these engines (all alluminum) are very sensitive to overheating and it can lead to very costly and serious damages. It would be a shame to ruin your new engine due to a blocked rad or sticky thermostat.

Be systematic in your diagnosis and be very wary about allowing the engine to get too hot. Coolant blowing out past the cap is too hot! Good luck!

 

You can always give it to someone else................

Raffle it off................

Make sure to keep plenty of water with you and coolant (green stuff only, not the Orange stuff) everywhere you drive it until it is corrected.

Do not drive it with it overheating.

A few questions:

Why was engine replaced?
A new one, a used one, a rebuilt one, or original one rebuilt?

 

The engine was replaced because it was only running on 4 cylinders... I am not entirely sure why that was though.

The "new" engine is a used one that came out of the mechanic's (a family friend) old Rover... it was not rebuilt.

 

You mentioned it was running on four cylinders, the VSS (Vehicle Speed Sensor) will cause the ECU to command one bank to shut off then both if it detects an overspeed error, which could be the sensor itself.

If he pulled the original engine and merely put in an old one, you could be looking at a multitude of unknowns.

Was the replacement from "An old Rover" that closely matching to what was in there?

Original problem cause was basically undiagnosed and the change may not have resolved that issue and could have introduced new ones as well or you may be lucky and just be facing a few relatively minor issues.

GOOD LUCK!

IF YOU COULD JUST SELL RAFFLE TICKETS CHEAP ENOUGH AND SELL ENOUGH OF THEM TO ENTICE BUYERS, YOU COULD DO WELL BY RAFFLING IT OFF. THINK ABOUT IT!

 

The engines were nearly identical.

Also, the cause of the 4 cylinder thing had to do with blown heads or valves or something... there was physical damage to the motor.

 

I have a feeling this 'free' vehicle is going to cost you...

 

OK, time for the 15 minute overheating dance...

1. Got coolant at mid point in coolant container? Yes = good.

2. Got white smoke out exhaust? Yes = Bad

3. Idles without overheat = good for serveral items. Fan clutch should be OK, because at idle is when it does the most work. With engine off, fan should have some stiffness, even with engine warmed up. Should not spin more than one revolution when spun by hand and released.

Since enginewas worked on, fan blades might be backwards. Cupped side of blades go toward block.

Belt route might be wrong, making water pump run in reverse, see tech area for belt route.

My PO added the twist of replacing the electric condenser fans, and wiring them reverse polarity, they subrracted air, rather than adding to it. Would only show up if AC was on.

Analysis of no over heat with heater on means regular main radiator is just barely keeping up. Mine had gobs of mud in the fins, and trash between the main radiator and the AC condenser, pull out rubber strip and examine.

4. Old owners are prone to try "stoz leekz" heavy duty formula, even Oklahoma grade extra duty formula, to deal with over heat, head gaskets, tec. It talkes a fingernail size piece to actually plug the leak, the rest settles to bottom of radiator and plugs it up, reducing the number of tubes available for water flow. Also, use of Dexcool coolant (orange) will degrade to a "mud - sludge" that does the same thing. Test is to warm up vehicle, until thermostat has water flowing, then turn off. Check fin area top to bottom, if possible with an IR thermometer. 10 -20 degrees difference top to bottom. A lot more than that, and no water is going thru bottom tubes, or it is going thru very slowly.

Radiator on our year is a copper and brass affair, about $600 new. An indy rad shop can hot acid flush, and un-solder a side tank and "rod" out the calcium build up, if radiator is not rotten. About $75. You can remove top radiator fill plug (battery side) and look inside with flashlight, if you see white crusts on tubes it will be worse below. Distilled water = good, tap water = bad, well water = worst thing you can do.

5. Could be thermostat, about $10, get the kind with a hole or jingle device, that goes at top of mount to let trapped air get by. 192-195 is stock, 180 run by some, 160 too cool, and some fools run with none (water temp will stay around 130 - 145). Or drill your own 1/8 inch hole in the base plate. If air is trapped behind stat, it dowes not react as fast as when in water. Try this next time you have a pot of noodles cooking. Hold hand over pot in steam. How long until you pull away? Now put hand in with noodles. Bet you'll react faster, just like the thermostat (kidz, don't try this without mom and dad).

6. Gauge is not to be trusted, it takes a long time to show over heating. Above 9:00 is problem. Plug in a scanner and read coolant temp just like the ecm, one degree at a time. Consider an Ultra Guage, which lets you dispaly lots of parameters and set alarm points, etc. Main thing is that when testing cooling, a digital display will tell you that problems exist before temp climbs too high.

 

I too thought about the belt routing but he drove it for four hours. Wouldn't the alternator also be turning backwards and thus kill the batt? I don't understand how the belt can go on wrong though so it's hard for me to speculate on that...

 

Alternator is an three phase AC geneator with diodes to convert to DC, it does not care direction, it will make DC. Belt route could be wrong, and decrease cooling flow, even though outside air blast is cooling things off. Top and bottom hoses should be different temps, but Mark I palm reader is not very accurate.

Of course, could have cracked block, bad head gasket, etc.