I have replaced the thermostat , and the water pump, engine comes up to temp when idling but not getting heat through heater box/ dashboard then it overheats really bad within a couple miles ! pleas help I am stuck someplace I dont want to be and need to get away, thinking of flushing heater core next. its a 318 not a 218.

 

Need more info to help out with diagnoses like has the radiator ever been flushed, are you sure you go all the air out of the system when you changed the t-stat, have you checked to see that the clutch fan is working properly, and do you know what the temps are at the top and bottom of the radiator as it is getting ready to overheat?

 

Warm it up, turn it off, and feel around the radiator core. It is probably plugged and will show this by having cold areas in random spots around the radiator core. If the radiator is plugged you will want to replace it.

 

I have flushed, but grit is still working its way out , very hard water deposits here, thanks for the responses . the fan clutch I would not know if its bad or not, I will try to burp the system and feel for cold spots on the radiator. thanks guys.

 

If you can safely grab your radiator hoses with the car running you can get it up to temp and see if the hoses top & bottom are both similar temps. There should be no more than 20 to 30 degrees difference between the top and bottom hose. If the bottom is substantially cooler you have a plugged rad.

 

When it's finally boiling over the steam is shooting out on the lower right of the heater return tube. If that helps any.

 

It sounds like you are describing 2 different problems here Mark. Your heater core isn't what is causing your overheating issue. If the heater core is plugged you just won't get any heat. If your truck is overheating you have either a circulating problem or some plugging going on in the radiator. Look in the top of the radiator and tell us what direction the coolant moves as the truck is warming up. It should be going from where the upper hose connects to the rad towards the other side. When you get to the point where the heat gauge is close to midway on the scale you are approaching the point where the t-stat is about to open. I used to read in the heating journals at work about aftermarket t-stats and the problems they can cause. One story in particular talked about a repairman that was working on an MG and having issues with overheating. He had replaced 3 t-stats and finally went to the dealer and got an OEM t-stat and his problem was cured. That may not be your issue but it wouldn't hurt to eliminate that . Other stories were of people putting Serpentine belts on wrong and making the water pump turn the wrong way. Honestly there are so many variables that it may take time to figure out the problem. I see people talking about Flushing their radiator. Most usually they are talking about using a garden hose to flush with. That is simply a rinse and NOT a flush. If you can borrow a thermal gun it would help you check the rad temps and let you know if the rad might be plugged. Is your rad an Aluminum rad or a copper/brass rad?

 

All of these symptoms can be the result of a blown head gasket. I suggest a leak down or compression test of all cylinders before doing anything else.