Ok, first off, I'm new to the forum and I'm looking forward to finding some great info as I read around.

Secondly, I come asking for help. I've got a '97 F-150 4.6 V8 and it's overheating and I don't know why. I've been having a problem with it for about 6 months and can no longer trust it to even run down the block. Thing is though, everytime it overheats and spews anitfreeze from the cap, I replace something and I'm running out of things to replace. So far I have replaced the T-Stat (twice--now has a fail safe), fan clutch, water pump, overflow cap, upper hose, flushed heater core (flushed it a while back due to low heat output), and checked it for gases. So, I know it's not a head gasket according to the chemical test. I guess the next step is to replace the radiator but I'm pretty broke and want to make sure that it's bad before I shell out upwards of $200 on a guess. I checked to see if I could have it "rodded out" but no one will do it.

It will overheat whether I am on the highway or the street, high rpm or low, and I noticed today as I was trying to figure out what exactly sets it off that it would sometimes start to overheat and then back to normal just as quickly which makes me think there's air in the system or a floating/circulating blockage. It overheats, I stop and relieve some pressure via the overflow cap and then the temp goes right back to normal and I can drive it sometimes for 10 miles, sometimes for 10 yards. It's just so random that I can't figure it out.

Has anyone else ever had this problem? Does anyone have any ideas of what may be wrong? Is there any good way to test a radiator? I appreciate any info and advice. Thanks in advance. Sorry for the long post.

 

Anybody?

 

The rapid movement of the temperature gauge suggests that there is air in the system. Coolant just doesn't heat up nor cool down real fast.

Verify the fan belt routing to ensure that the water pump is turning in the right direction.

Are you running a 50/50 mix of antifreeze?
Is your radiator cap in good shape?
The reason I mention these is that both are important to keep the boiling point of the coolant well above the normal operating temperatures, so that there won't be any flashing of the coolant from liquid to vapor.

Did you replace the thermostat with the OEM-recommended temperature grade? Some like to use a higher temperature for more heater output or whatever, but recommend to stick with what the manufacturer specifies.

What kind of shape was your coolant in when you did the heater core flush? If the heater core was fouled, chances are better than average that the radiator is also fouled and could use a good flush. For it to be at the point of this level of overheating suggests that it may be just flat blocked up.

If you can run a garden hose full throttle into the radiator filler or upper hose inlet, and it comes out the lower hose outlet just as fast, then there's hope that a flush can do some good. If the inflow exceeds the outflow, going to take more extreme measures. Suggest to try running a good flushing agent through the system.

Another option is the radiator shop - they can chemically 'boil' the core in some kind of bath, but this usually involves removing the reservoir tanks nowadays due to the plastic. Then one has the worries of whether they get the tank gaskets set back right for no leaks.

A new radiator may indeed be on your horizon, but suggest to investigate and to exhaust all the easy and cheaper measures before springing for this.

Good luck, and keep us posted.

 

Belt's fine, radiator cap is brand new, anitfreeze is 50/50 and fresh, thermostat was replaced with the OEM equivalent except I went with a fail-safe one this time.

The thing about the heater core was that I wasn't getting any heat in the cab and figured since it's somewhat common in F-150's for the heater core to crap out that I would try flushing it before replacing it. However, after flushing it, the heat didn't really come back. I thought it was slightly warmer but, to be honest, it may have been the same.

Boiling it isn't an option. I called the best radiator shops in town and they all told me that it's probably clogged and there's nothing they can do (rodding it out, boiling, etc.) other than selling me a new one.

Thanks for the advice, I'll try running a hose through it and see if I can brake anything loose.

But if anyone's got any other advice or options, please, please let me know. I'm at my wits end. Thanks.

 

I've read here and there of people having the same issue but they never post up what they did to fix the problem. I've got to do something by the end of the week so if anyone has any ideas, please let me know before I dump the money. I really can't afford it but I can't afford to have the truck out of commission either. Any help would be appreciated.

 

do you have circulation ???

 

I think. I mean, sometimes I can drive it for 50 miles with no problem and sometimes I can't even make it down the block. That's what has me confused. I hate problems that occur randomly. I seem to be plagued by them.

I guess it's possible that I have a floating blockage or air in the system but even still, it doesn't make sense how random it is.

 

Replaced the radiator, flushed heater core again, flushed engine block and pulled the water pump to check it. Water pump looked great and I couldn't get it to slip if I wanted to. Anyway, brand new radiator, filled with 50/50 mix antifreeze and distilled water, drove it for about ten miles on both highway and street and while sitting at idle in a buddy's driveway for about ten minutes it blew it's top again. Everybody keeps telling me there is air in the system but I don't see how. Everything was done by the book and, as far as I know, there is nothing left to replace. So what the hell is the problem?

I've now dumped about $500 dollars that I don't have into this problem without payoff. I can't afford anything else. Any ideas guys?

 

Other than the overheating, it runs well? Severly plugged Cat could cause overheating. Timming advanced too far. Belt routing. No blockage in front of the radiator, between or infront of evaporator? You're sure the water pump is good? Bearings, impellers? No water in oil? Not real familiar with newer system, is there any kind of heater bypass system that could be malfunctioning? Other than the work of the devil, I'm out of ideas.

 

Only reason I mention the blockage is because I was at a shop that had a corvette. The customer complained about overheating. He had dumpped a bunch of cash on hoses, belt, flush, cap, and thermostat, as well as many hours of busted knuckles anf frustration. As soon as the car was on the lift a mechanic pulled a plastic grocery bag out of the evaporator. Problem solved. Rare yes, but I had a mis because a mouse ate my injector wire, s#it happens.