This is a 1997 Ford F150 truck with 132,000 miles on it, V6, 4.2L, 4WD. The problem just started recently....it is not a consistent problem....the heat will start off blowing proper temp heat, sometimes it goes to lukewarm, it will go back to hot air, then it will go to cold air. It is not consistent...you can have the heat in the red blowing hot and then it goes to cold. The mechanic has backflushed the radiator, heater core, and the engine block. Put a new thermostat on, put new heater control switch on, the dampener door that opens and shuts underneath the dash is working properly. Temperature gauge will shoot up, but then comes right back down on occasion. He put new intake gasket b/c was hearing gurgling sound and that is resolved, but did not solve heat problem. Brand new water pump on it also. Nothing seems to resolve the problem. Does anyone have ANY idea what the problem could be? The mechanics are kind of at a standstill not sure what else to try. They say the water is coming through the radiator and heater core just fine, water is nice and clean. Several people have said it could be a cracked head, but the engine runs fine, no steaming, no water or oil loss or anything that indicates a blown head gasket. The mechanic feels it is a flow problem somewhere, but does not know where. Any suggestions would be greatly appreciated!!! Just cannot keep pouring money into this. Thanks to all!

 

I dont know your mechanics so I dont want to knock them but you can check the flow simply by feeling of your heater hoses when you have the heat on. Both of them should be about the same temp when you are running heat. If one is colder than the other you still have a flow problem. It really sounds like a flow problem. You also should check your cooling fan to make sure its functioning properly.

 

your mechanic needs to slow down and think for a minute. he is replacing way to many parts. Like 54Ford said, are the hoses hot to the heater. If so, then it should have hot air. If not hot air then the mmixing door is broken or the heater is plugged or coated with calcium/ fouled. The temp gauge should tell you also what is going on. You have way to much conflicting data. If the air goes from hot to cold and you did not move anything, then the blend door moved or you ran out of hot water flow. Thats when you check the heater hose temp.

 

that is why he knows there is a flow problem, but he doesnt know where. As for the temp gauge, as I said before, at times it will start to rise, but then immediately drops back down w/o any true overheating of the motor.

 

if you have water running thru the motor and thru the radiator fine, then its not a flow problem. thats what im saying, its a little confuseing. When the temp gauge rises, is it in the normal range, then jumps way up to hot and back down, or is it cold, starts to go to normal, then drop to cold again? If your not getting to the normal range, then the thermostat is bad. If the thermostat opens and your about normal, then the temp gauge jumps way up to HOT and within a minute starts to drop back to normal, thats another problem. I had a small crack in the head or head gasket that would allow compression gas to leak into the water jacket and set around the temp probe when the motor was off. When you start engine and the thermostat is closed, the engine started to warm up normal, but there was air around the probe, no water, becasue no flow, because the thermostat was closed. About the time the thermostat started to open, the air was HOT and the gauge would spike up. Within a minute the water was flowing and the gauge would drop back to the normal range. I was also using some antifreeze at that point. If you never have any usage, its hard to believe you have a gasket problem.... when does the gauge spike?

 

Im not sure about a 97 but some vehicles had a heater control valve in the middle of the heater hoses that can cause a lot of problems too.

 

ex. stopped at a stop sign and when took off the gauge spiked up. Another time when stopped in traffic to make a left turn and it spiked almost into the red, started to pull over b/c thought it was going to overheat, and suddenly dropped back to normal and the heat was blowing cold air. After that the heat went to lukewarm and then hot and for the rest of the 18 mile trip the temp gauge stayed in normal range and the heater blew normal hot air.
As for using antifreeze, I dont know, b/c the mechanic has had the truck longer than I have lately, but he has not mentioned it using. Right after he blackflushed everything at the start of all this, the first time I drove it again the temp gauge shot up, the oil light came on, AND it blew antifreeze all over the motor that time, but that was the only time that I know of.
BTW, I appreciate all the input...Thanks.

 

your low on antifreeze and have the air bubble in the top of the water jacket as i said. either you need to put a vent valve in the heater hose to vent the air off if is just vapor locked, or you have a pin hole in the head or gasekt as i did. Mine did EXACTLY as you said. take off from a stop and the gauge spikes. Normally within 1 minute it will start to drop. The gas/ air buildup normally causes the tank to overflow a cup of antifreeze. you get no heat becasue there is air in the heater core not water.... You need to flush the system out, put BARS head gasket repair in the system with water and drive around for a while ( an hour). Flush and refill, put a vent or flush TEE in the heater line while it is empty, that helps you blead all the air out, and helps to flush the system with a garden hose... I did this, it works great..

 

read this post, then at the bottom go to the BARS page. They sell this stuff at Auto Zone.

https://www.ford-trucks.com/forums/8...lant-blow.html

 

I have copied and printed your responses and the info. from the link you posted and took them to our mechanic. He said it was really good info. and he is going to try doing what you suggested. If you think of anything else that might be helpful, we would greatly appreciate it. I will let you know how it goes, and again, thanks!!

 

It didnt work....ugh! This is so frustrating.

 

You can actually see the flow in your radiator if you drain enough out to see a few inches down inside the radiator where the cap goes and watch the water flow through the fins. If its not a good steady flow it is most likely stopped up. Another no cost way to check the flow. Best of luck.

 

your missing something. the info your presenting and all the parts that have been changed out are not going along with the ongoing problem. what is it doing now?? When i got all done with the fixes and using the gasket sealer, i had a spike now and then. Found out the blead hole in the thermostat was plugged and could not vent off or let hot water leak thru to start the thermostat warming... One thing i did was cut the little ball-pin out of the thermostat bleader hole. It takes a few more minutes to warm up now since i am leakingn more hot water thru the thermostat and not keeping it bottled up in the engine. I NEVER have the spiking ot thermostat sticking problem since i cut that little ball out. I attribute the pluggage to the gasket sealer. If affected the thermostat, but will not plug the heater or radiator.