I have a 97 F150 4.2 V6,runs hot when I run the A/C or when pushing it on the interstate.I can turn on the heat and fan on high and she'll cool back down.I'm thinking it is clogged radiator,cause I've replaced the thermostat and same thing happens.Fan clutch checks out o.k.,and the water pump seems to be working?Who has the best price on the double row radiator,I'm thinking this thing has the single row?How do you tell? This is just one of the problems I'm having.Thanks in advance for your advice and sympathy. 97fone50

 

97,how do you know the water pump is ok?Did you grab the upper hose and squeeze it to feel the water running thru? If the hose feels very very hard when you squeeze it and cant feel flow then your thermostat is probly stuck.And the clutch fan,how did you test it? Is there little resistance when you spin it or does it(fan)spin a few times? How often have you flushed the system? It very well could be your radiator.You can always pull it and have a shop do a flow test on it.Good luck and keep us posted!

 

is the coolant full? I don't mean to point out the obvious, but I've overlooked some things before.

 

Hi Guy's,thanks for the replies.Yes,I have been checking the coolant,yes I have checked the upper radiator hose and it was to darn hot to keep a hold too. Changed thermostat already,while I was re-adding the anti-freeze I would rev the motor and watch the reserve tank drop then rise as I let off the gas,this is another reason I think the water pump to be good.Any other ideas?
Thanks again fellas'. 97fone50

 

Before I install a thermostat I always check it on the stove in a pot of boiling water to see if it opens/closes.Did you check yours?I'm thinking your new thermostat is bad too.Or,your water pump is cavitating.I cant really give you a solution due to it not being in front of me.If you still have the old thermostat check it on the stove in a pot of water.If it opens,you know that it was good and can eliminate that.Does the bottom hose collapse as you rev the motor?

 

Whoops,I did think about about checking the old thermostat,in a passing thought. I was so sure that was the problem I didn't check it and tossed it in the trash.No,none of the hose's collapse when revving the engine.What do you mean by water pump cavitating?Never herd that before? Thanks for the replies Guy's,97fone50

 

Cavitate is when the impellar is free wheeling or spinning and not moving water.Usually caused when there is an air pocket.

 

Thank you for your reply,BlueOvalFitter.I won't rule that out.While I was changing the spark plug's,I removed the fan belt and checked to see if I had any play in the water pump shaft.There was no loose play.I'm going to take it to the radiator shop and have a flow test done on the radiator and see if it need's rodding out.What do you think? 97fone50

 

I recommended that early on.Lets look at it this way;it can only be (1) of (3) things causing this problem; thermostat,water pump,or partially clogged radiator.One more question; how do you actually know it is over heating?Does it boil over?Could it be a bad temperature sending unit?Or a bad gauge?

 

When the gauge is reading it is hot,I tried to take the radiator cap off and she started to overflow,this was done while the engine is still running.When I check it when it is at normal temp.(removing the radiator cap) it doesn't try to overflow but remains a constant level,and I can remove the cap completely. 97fone50

 

Man,that sure sounds like a stuck thermostat.

 

What do you think about just taking the therostat out completely and see if it run's hot?This time while I have it out,I will check it on the stove in a pot of water,like you said.Last night the wife and I went to dinner,running through town with the a/c on,stop and go traffic.Didn't run hot,it also was right at dusk so it wasn't as hot as midday when it has been running hot. Thanks again,97fone50

 

Do as I said earlier,grab the top hose and squeeze it to feel the water going thru it.If you say its that hot to hold then that raises a red flag.I'm out of answers for you.Yes,pull the thermostat and check it in water.Make sure you have a thermometor to check the temperature at opening.Go have your radiator checked.If those two things are ok then that leaves the water pump.Good luck and keep us posted! If you want talk to me on the phone email me at wrr01@aol.com

 

Thank you BlueOvalFitter,I appreciate all your help.Saturday when I replaced the spark plugs I tried something.Instead of cranking down the radiator cap till it clicks three or four times,this time when tightening I only made it click once.So far it has not run hot,but it also hasn't been as hot outside as it has been? Thank you again,97fone50

 

Over the last week I've been having the same problem with my 97 F150 (91K miles). As the outside temperature moved into the mid-90's the engine overheated if I went more than 60 mph.

After reading this thread I went through the steps... (1) cleared junk off the radiator, (2) power flush and fill with 50/50 mix of coolant and water, and (3) pulled, tested and replaced the thermostat. The thermostat was not opening fully. Replacement made it better, but did not cure the problem.

Took it to the dealer yesteday. The water pump tested good for flow and pressure. It ended up being a partially plugged radiator. They pulled the radiator and had it rodded. Problem resolved. She runs cool at all speeds.

In the end this little adventure has cost me around $300 for coolant, parts, and service.

Thanks for all the suggestions in this thread. It helped me isolate and solve my problem.