QuestionHi John,
I recently bought a 02' Disco SE7. It has been running great until the other day. After a long trip the engine started overheating. Needle started rising and went right through the red zone. I pulled over and let it cool then filled it with water to make it the remaining 5 miles home. I figured it might be the thermostat so I replaced that, replaced the coolant and tried again. The Disco overheated again, but it didn't happen until I had selected 4 wheel low to see how the engine would handle a load. The needle again went right through the roof. I called the LR dealer and they said it might be a cooling fan or possibly air in the system. I got another cooling fan but it too does not seem to work. The dealer said the coooking fan should come on when the AC is selected but accoording to their maintenance manual it looks like the engine needs to be fairly hot before this will actually come on. I did not notice the fan on at all when the vehicle overheated but I was not looking for it either. I checked the fuzes, all look good. Here is the bad news, after replacing the cooling fan and running the engine I noticed some steam coming from the exhaust. I am wondering if its a head gasket? So I guess I have multiple questions, 1) How do you know if the cooling fan relay is good or bad? 2) How do you know if you have sufficently bleed the system? 3) Does it sound like a head gasket problem and what do you think caused the orignal overheat? The head gasket or the original thermostat?
Thanks,
Garrett
AnswerHi Garrett,
first of all...be very careful with this problem. If your engine overheats too severely, you could loose the cylinder sleeves. The welds could fail and the sleeves could drop THUS ending the engine entirely.
Steam coming from the exhaust is not a good thing. At best you have condensation buildup in your exhaust pipes and at worst your headgasket is a bust.
Did you pressure test your engine? How about the radiator? Either could reveal the condition of your cooling system. I hope its just the radiator that's causing you the problem...its easier to repair and costs less.
In your case, I doubt its the fan or the relay. This past summer, I had to replace my rad after 11 years! The Disco was overheating and I too replaced the thermostat in a vain attempt to solve the problem. A pressure test revealed that I had micro leaks and blockages in my rad.
Coolant does not pass through radiator freely. Over time, chemical reactions can cause corrosion buildup in the radiator tubes and can restrict the flow of coolant through the radiator.
Also, debris can accumulate at the tube openings similar to a strainer, and the resulting blockage can restrict flow. The result is that the heat is not transferred from the coolant to the fins and overheating will likely occur.
Air flow was restricted through the radiator and the heat cannot be dispersed properly. After 11 years, the buildup on the forward facing fins of the radiator also did not help the air flow. This buildup of heat can cause overheating.
Over time, the metal fins oxidized and deteriorated. Its only natural that road salt contributes to speeding up the oxidation process of radiator fins. From the engine side, all looked well...but on the forward side - it was a mess.
Here's what I did when I installed my radiator this summer. This explanation includes my method of testing the relay and the thermostat while bleeding my system:
Air rises to the top of the cooling system and gets trapped, causing the cooling system to vapor lock. If the radiator is made the HIGHER point in the system, the air will escape into the radiator where it will be vented out through the radiator cap or the overflow system.
To vent a system in this method, raise the car so that the radiator is higher than the water box and engine. You can do this through jack-stands, ramps, by parking with the nose of the Disco pointing up a hill. Do be extreme, just enough to allow air to move forward and up.
You'll need to let the Disco warm up so that the thermostat opens for the system to vent in this method. Never open the cooling system when hot or you could end up with a hot shower of antifreeze. Let the car warm up from cold with the radiator cap removed. You may get some spillage while the coolant expands and the air bubbles out. Be careful as this coolant will be hot.
Allow the engine to run, with the heater on (fan can be off or on low) until the thermostat opens and all the air is allowed to purge. Once the thermostat opens you will see the coolant level inside the radiator bubble and drop. Continue to add antifreeze to maintain fluid level.
Again be careful as the coolant and any steam released by the system will be hot. Once the upper radiator hose becomes hot to the touch and no further air issues from the system carefully replace the radiator cap and ensure the overflow bottle does not run empty.
Continue to allow the Disco to run and allow the temperature to stabilize. If you don't have a temperature gauge, allow your Disco to run until the fan cycles on and off at least once (the relay test you asked about).
During this time ensure there are no leaks from the system and that the upper radiator hose gets hot to the touch (especially close to the radiator). If not then allow the system to cool, and repeat the steps above to purge any remaining air.
If you are not comfortable leaving the radiator cap off during warm-up then you can accomplish the same thing by leaving the radiator cap on and allowing the car to cool down. REPEAT the above instructions SEVERAL times, allowing the engine to cool down between each cycle, making sure the overflow bottle is maintained at the proper level. The heating and cooling cycle should push the air out through the overflow bottle and then suck coolant in to replace the air when the engine cools. The car must remain inclined for the whole procedure.
I hope this helps you out,
JohnMc
