Cooling system questions

[Turbo_Bimmer]

Hi,
I need you advice on this one please.

When I bought my 93 E250/5.8L (170000mi) a couple of months ago, the engine was overheating, going in the red zone during normal driving (Florida summer). Since the price was right, I bought it as is.
On my way back, I had to stop to a shop to have the radiator and thermostat changed so I can drive the truck. They put a brand new radiator and thermostat (chinese brand). There was no thermostat installed in the housing, which was the cause of overheating according to the mechanic.

So, after the repair, I took the highway, and the truck was not overheating anymore under normal driving.(up to 65mph). If I was driving over 70-75mph, the temperature gauge was going in the red zone immediatly. If I released the gas to drop below 65, temperature came back to normal.

Also, another strange behavior of the gauge, was that, during normal driving, it stayed in the middle for a long time, then for no reason, started to climb to 5/8 or 3/4 and then immediatly dropped to 1/4, like a cold engine. Slowly, the needle came back to the middle.

I only had a chance to work on the truck this past weekend. I installed a new Ford thermostat, a remanufactured water pump, and installed a wire wound (spiral reinforcement) inside the bottom hose to help prevent collapsing.

I went for a test drive today. On the highway, I was succesfull driving the truck up to 85 mph without going in the red zone. The needle was continiously but slowly fluctuating from 1/4 to 3/4. Is the overheating problem fixed. I don't know since now we are in winter with temperatures below the freezing point.

What I don't understand, is the fluctuating needle. All the cars/trucks I owned in the past, always had a steady temperature gauge needle in the middle position. It's the first time I see a needle moving that much. Is this normal on that kind of engine?
Is there another problem somewhere, like air in the system, bad head gaskets?

The van will be used this summer has a tow vehicle for my racecar. It needs a good cooling system and be reliable.
PS: I don't know if it's related, but the heater blows only warm air inside the cabin.


Any help is appreciated.

Thanks.

[ghcoe]

I would replace the temp sender to the gauge and to the computer, if they are not on the same circuit. Could be getting faulty signals. If the computer can not get a accurate reading it will try to compensate for nonexistent problem and cause temp fluctuations. Or it could be running fine and the sensor for the gauge is giving faulty readings. I would replace one at a time though to help isolate the problem.