Overheating 1998 Discovery Series 1

[pboerger]

This has been a long story. I have replaced:
Thermostat
Temp Sensor (for ECU not guage)
A/C condenser fan (it was burned out)
Main Fuel Relay
ECU (I shorted it out)
Sepentine belt.

The car still overheats with the temp cycling up and down rapidly so I think I probably still have an air bubble in the system. Also the condenser fans are coming on and going off as if they are getting intermittent power. I can hear the relay clicking on and off inside the car. Finally I want to verify the main fan's clutch is engaging.

1) Could the condenser fan relay be faulty and go on and off?
2) How can I determine if the Fan Clutch is being engaged?

Thanks,
Phil

[John C]

Spin the fan by hand when it's cold, it should have some resistance.

How's the rad?

The condesnor fans are going on and off because the engine is overheating. I would worry if the fans did not go on at all.

[02disco2]

Is the water pump bad? There is not much to the cooling system, sounds like you replaced about everything else.

[pboerger]

There is some resistance on the main fan when it is cold. As far as the water pump I am not hearing any noise. Is there another way to tell if it is working?

[parthog]

As the engine warms up, you should feel hot water getting to the radiator via the top hose. If the engine is heating up and the water to the radiator is not, I'd suspect air in the system first, try bleeding the system.

[Disco Mike]

When at an idle, after the engine warms up is your heater cold, warm or hot? If cold, does it warm up if you run your idle up to 2000 RPM's for a couple of seconds?
Mike J.

[pboerger]

The heater is warm at idle.
Recap:
Starts easily and runs smoothly. I can travel about 10 miles thru town while driving between 30-40 mph interrupted by traffic lights and stop signs at normal temperature. Then the temperature starts to climb fairly rapidly. It will fluctuate up and down. If I rev the engine it tends to lower the temperature. The condenser fans go on and off intermittantly and do not seem to run as a result of the temp guage. My OBD-II scanner shows coolant at around 232-240 degrees. The reading will fluctuate up and down by a few degrees while running.

I am not sure the main fan is working. Also I am concerned by the operation of the condenser fans. Plus I think I may still have a smaller air pocket in the cooling system.

Later tonight I am swapping the condenser fan relay (yellow multi-use) to see if that is a/the problem.

[parthog]

Not to be a pain, but with an iron-sleeved aluminum block and aluminum heads I wouldn't drive around until the problem is solved.

[pboerger]

I ran the engine with my OBD-II scanner attached. The coolant temp slowly climbed at an idle. Running the heater at full blast and/or increasiing the revs would lower the temp but at idle with no heater running the temp would creep up.

I imagine this is what is happening as I drive. The temp is slowing working its way up. Its as if the main fan is not quite going fast enough to provide the cooling necessary to maintain a steady temperature. This leaves me with a few questions:

1) What temp should the coolant stabilize at? I supsect it is around 220 degrees.

2) Would a failure of the main fan's clutch act like this? Is there anyway to know for sure the clutch has failed?

[plastic]

could it be your radiator is going bad?

[pboerger]

A friend at the dealership had the same idea. I am taking the car into a reccomended radiator shop on Friday to have the core cleaned. Hopefully that will solve the problem.

I am still concerned about the main fan. When I parked the car tonight with the temp guage reading normal I turned off the engine and immediately tested the fan blade for any resistance and it was free spinning. It seems to me that at a normal temp the blade should be engaged and have some resistance after shut down. As it was the fan must have been free-wheeling at shut down and that doesn't seem right.

[Disco]

Your radiator temperature should read 210-220F.

[Disco]

BTW, have you checked for a leaking head gasket?

[John C]

Originally Posted by plastic

could it be your radiator is going bad?

That's what I thought also.

I had a similar problem and after changing the thermostat, the water pump, the fan clutch it ended being the rad.

Got a new one for $375 (original) instead of $500+

[pboerger]

Today I took the Disco to the radiator shop and was informed the radiator was all "gunked up" and couldn't be cleaned without damaging it. However they replaced the core with a new one with wider passageways for the coolant. The whole process cost $285 including labor and fluids so I guess that's not too bad. I think it has solved the problem altough I guess wait until a few hundred miles have passed before I am 100% sure.

In the meantime I am looking for another series 1 1996 thru 1998. Since I am learning so much about this one I may as well have another so I can apply the gained knowledge to another vehicle!