Hi, looking for advice. My F150 seems to randomly overheat (suspect blockage). Will drive for a few days fine then temp randomly starts climbing into the red and I also start getting cold air blowing inside the vehicle. It usually corrects itself after a few mins. I have changed the thermistat and water pump. Haven't seen any drippage, leaks or needed to 'top off' coolant (except when changing the forementioned parts). Would doing a radiator flush using the drain **** on the bottom of the radiator allow this blockage to pass or should I remove the bottom radiator hose to flush it out?

 

Temp gauge spiking up to red and dropping within a minute is normally due to an air pocket at the top of motor. The sensor when not covered with water, is in the air and spikes quickly... The loss of heat thru the heater core is basically the same think. Heater core full of air. Might last a few minutes, then heat comes back. Both symptoms of low water level. I cant tell you if your have blockage or stuck thermostat causing waster loss, etc. I can recommend that you put a plastic TEE in the heater hose as far up as possible. I crack the cap when i am filling the overflow tank and stop when water starts leaking out of the TEE cap. Cap lets all the air out as you fill. Dont hurt to park on a slight incline so radiator is higher up than rest of motor. You might not have got if full after pump change, or you might be burning off somewhat slowly and not notice. Refill and monitor the overflow tank every week to see if it drops 1/2 inch or 1 inch over time.

 

What you said made me think back to when the problem first started and I suspect you are correct. I didn't think about it till now but the problem started after I had to replace my alternator and lucky me the upper radiator hose was blocking it so I disconnected it to get at the alternator. As there isn't a radiator cap I assumed the pressure/suction would 'fill the void' from the reservoir. I will see about installing a TEE radiator cap in the upper hose. Thanks for making me think. =)

 

Ok, follow up. First of all, where can I get a TEE, the local parts store here (middle of nowhere) never even heard of them (had to show him one on an '03 Dodge Durango).

My problem still exists though. As I'm driving around it randomly overheats and when it happens it starts to 'overflow' lots the coolant out of the reservoir tank. I discon'd the upper hose, lower hose and flushed the radiator and engine with a garden hose and didn't see any noticeable lack of flow (blockage). I've changed therms 2 times now and water pump 1 time. I have tried many 'tricks' to fill the radiator/engine with coolant and it seems full but the problem keeps coming back. I even jacked the driver front end to make that side higher than the upper radiator hose when filling and I even filled using the small 'overflow' tube to pour into the radiator. I have even 'massaged' (squeezed) the upper rad hose trying to 'prime' the coolant flow. I never see any leaks and only have to refill the reservoir tank after it overheats and it overflows out the reservoir tank cap. I have noticed that when it does overlow, it is not coming from the small overflow tube connected from the top of the radiator to the reservoir tank, it seems like it's being pumped up from the lower radiator hose. Also after filling and running the truck for a period the upper rad. hose seems to swell with pressure (very difficult to squeeze by hand) and I notice that the coolant in the reservoir tank goes down a bit but it seems like the upper hose fills up with more air again than coolant. Last but not least after refilling this last time I checked the upper hose for heat and it never got warm so I know it's not circulating.

So:

1 - What is the coolant flow direction.

2 - Can anyone give me something else to try?

Thanks for any tips/advice. This is really frustrating.

 

coolant should enter the radiator at the bottom and go to the engine from the top, could be a bad gauge or temp sensor, i would recommend buying a 15 or 20$ mechanical gauge and installing it to see if you are still having the same problem, had this issue with a chevy i did head gaskets on at my shop, put a mechanical gauge on it that we keep for testing purposes and everything was normal, ended up being a bad gauge cluster.
hope this helps

 

Thanks for your suggestion F150Racer, but since the upper rad hose wasn't getting warm there has to be a flow issue for some reason. Just don't know what the reason is and how to fix it yet.

Additional info I just remembered which may be significant. Didn't think about it at the time but while the truck was running I diconnected the overflow tube from the reservoir tank attempting to fill while running. If the pump is good (odds are the old one and new one aren't bad), shouldn't the coolant have been squirting out like a jetstream since it was still connected to the rad or since I depressurized it, it wouldn't?

 

no, once the pressure is off, it wont squirt. It also goes the other way. As motor cools down, it can suck water from the tank back into the radiator to fill it back up.

 

Ok, I think I finally got it. Here is what I did. I jacked up the driver front end. I released any pressure via the radiator cap on the tank then retightened the cap. I removed the overflow hose from the tank and and jammed a pencil to temp. seal the overflow tank from where I had just removed the hose. I then filled the radiator via the overflow hose as much as I could (did all this before but here was the clencher for me). After I got the radiator as full as I could via the overflow hose I got a cup and filled it with coolant which I then stuck the overflow hose into. While keeping the overflow hose in the coolant, I squeezed the upper rad. hose pushing out any air bubbles and forcing it to suck in more coolant. I continued to do this till no more air bubbles came out when squeezing the upper rad. hose. Now when running my upper rad hose heats up and so far I haven't had the problem again. (hopefully I didn't just jinx myself). =)) Thanks to everyone that helped with their thoughts and ideas.