I’m still working on the heating problem on my 1988 Bronco II 2.9L

When driving the temperature indicator goes up about 4 mm under the red hot line and then drops again slowly at the normal level.
I changed now the Thermostat, temp gauge and radiator pressure cap but nothing changed.
I do not lose any coolant and there is no coolant in the oil that good indicate a cracked head casket. In the coolant I don’t smell exhaust gases so it is not clear to me what is causing this.

Can this have something to do with the water pump or Fan clutch, and how can I test these.
I noticed that when the engine is a working temperature the fan can be easy turned by hand with a minimum force.

Ray

 

The fan should be hard to turn cold. Waterpump may be a problem but I doubt it at this point. Fan clutches can leak oil all over themselves when they go bad.

When it reaches max temp and then cools down, are you driving down the road or just idling?

 

When the engine is cold for me it seems that there is not really more force needed then when it is hot.

(When it reaches max temp and then cools down, are you driving down the road or just idling?)

On idling the temp is normal, so this shut mean that the fan cools ok, also when I drive and the temp is rising up it goes back to normal levels after a while. It seems to me a loop; the temp is going up and down. The new temp gauge installed did not solve this, the readings are the same as the old one.

 

The loop makes me think it has air in the system or you are low on coolant. I doubt both though in your case. The fan does raise an eyebrow for me. When those clutch fans are cold they are a bugger to turn, they either slip on the belt or you start turning the engine.

 

The coolant level in the radiator is good; also there is coolant fluid in the expansion tank.
As for the fan clutch it is really easy to turn when the engine is cold (I can turn it easy with two fingers), only a little force more needed to turn as when the engine is hot. So here good maybe the problem, a just want to be sure because it is here in Switzerland not cheap to let it repair.

Ray

 

Something you might do is listen for your fan clutch to see if it pulling air through the radiator. You can tell a big difference in sound when a fan is pulling air as opposed to it "windmilling" and not pulling air.

When you replaced your temp gauge did you make sure it had a good ground? The last thing that could be checked is the water temp sensor itself that is located in the block. It may be your system is just fine and the water temp sensor is going bad.

 

It is pulling air through the radiator when the engine is cold, this I can hear loud and clear.

Sorry, I changed the temperature sensor not the gauge, this seems to me working well.

I tried almost everything; it is difficult to find out what is wrong.

Ray

 

Today I drive about 250 Km on the highway and after a short while the temp claimed up again and staight at the high level, When I came home I checked the coolant and everything was ok, also the radiator was not overheated or extremely warm when I toughed it. I looked at the front and see that there are 2 or 3 small radiators look-alike in front of the main radiator. The large one is the condenser of the AC I believe, this one seems to me full of pollution, I am not able to see trough (cheque with light), if this is blocking the fresh air this good have something to do with it. I have also a new spare condenser and here you can clearly see trough.

Ray

 

Yes, by all means clean the condenser. I don't think it would cause the loops you are having but it would definately help your system.

When your system shows it's getting hot, do we know for certain that the engine is overly warm?

 

Hi again,

Well that is a good question; I will cheque these with a digital temp meter in the radiator cap hole at the top to see what the actual temp of the coolant is. This good gives us a glue.

Ray

 

Is there a resistance table for the temp sender available somewhere so I can measure the sender’s resistance at operational conditions?

Ray

 

A good manual should have that. If you don't have access to one I bet we can find that information for you.

 

Is this the orginal water pump? How many miles on it?

 

It is the original water pump. The car has now about 95000 (150000Km) miles on it.
Tomorrow I will install a new radiator just to be on the save site, also I will change the condenser in front of the radiator of the AC because it is full of pollution and I don’t think that enwove air can be polled trough.

Ray

 

Here is what I think. Your waterpump is worn and causing cavitation (air bubbles) in your system. It doesn't overheat while idling because the pump just isn't spinning that much. Once you start driving, the pump pumps a lot more and causes air bubbles in your system. The engine starts overheating and you pull over to let the engine cool. The air bubbles slowly leave the system and the engine cools as it's supposed to.

This would explains the cycle (at least in my mind).