I have a 1990 Ford Ranger 4.0L, 4wd, fuel injection with auto transmission. The heater hoses/ system makes a thumping noise. After the truck has warmed up there is a series of thumping noises under the hood by the heater. When I open the hood I can feel the water pulsing in the heater hoses, and the hoses seem inflated or firmer. The temperature gauge reads low - so the truck does not appear to be hot. and it does not do it all the time, It is random. The overflow bottle does not appear to have gas in it and the truck is not losing coolant. I notice it most when the truck is stopped or idling because there is too much road noise any other time. It will continue to make the noise after the truck has stopped.

The truck just recently had a blown head gasket, which was replaced. The thermostat has been replaced twice, 1st time was when the head gasket was replaced and the 2nd time was when I started hearing the thumping.

My mechanic is baffled - He says it is an open system and he dosen't know what is happening. Can you guys help??
Thanks
gja7

 

Yes, it sounds like air is in your system. More common in Windstars though. Your owner's manual should list the procedure, there are various methods to get it out, I will tell you the easiest one that will probably work the first time.

Lift the front of the truck so the radiator is much higher than normal and the heater core is much lower. I would say lift it about four inches higher than normal. Use a tape measure. Right now your heater core is probably sitting equal/higher than the bottom of your radiator.

Then bleed the truck by running it with the radiator cap off. Turn on the heater AFTER the thermostat opens. The air pockets should bleed to the highest point, your open radiator cap.

This is easier to do on a lift, but, since your "technician" is so stumped by this, do it yourself. Get a floor jack that will lift the truck 18 inches (jack it up by the axle one side at a time) and 12 ton floor jacks. These jacks are usually tall enough 16-24 inches so you can jack up the truck by the axle and then stick them under the frame rails on both sides.

Then you will have all you need to do more work on your truck yourself and not have to rely on someone that can not bleed a cooling system for a customer when they return the second/third time.

There might be a chance of having a bit of RTV or gasket stuck in your heater core and having to back flush it, but, I doubt it. This should work.

Hope this works for you.