I ran down to the store today in my 1986 F-150 ...4.9 six

I used it a few weeks ago for plowing ... worked great

At a stoplight (I had been driving for about 20 min ... heard "something" odd when idling)

Didn't notice anything so went into Home Depot

When I came out of the store, I noticed a puddle ... water had come out of the overflow (stopper went missing years ago).

Started fine ... temp gauge was a bit high but nothing to right home about ... came down soon as it ran for a few seconds.

Drove home ... temp needle sat right in the middle (which is a bit high for the truck but then we are 40 today ... not our usual 0 )

I stopped to grab a coffee ... came out ... puddle on the ground ... again from the overflow

Came home ... got to the end of my street ... steam from under the hood ... temp gauge reaching the upper limit

Popped the hood ... again from the overflow bottle ... it was half full of coolant (I am guessing the rest boiled of .... hood is wet right over the vent hole).

I watched as it cooled and the coolant was sucked back into the rad ... sucked it dry .. I had some antifreeze/water mix ... added it ... sucked it dry ... then sucked air.

So where do I start to look?

I think the water pump is about 2 years old.

The rad split the plastic case last year so it is new

I put a new thermost in it then.

No water in the oil ... and do thin there is any oil in the water (hard to check).

No air bubbles in the rad (so probably not a head gasket)

Just not sure where to start looking.

Thanks .... Mike

 

Check the radiator cap. Take it off and turn it over and see if the rubber or the brass washer under the cap is cracked. Or just get a new cap. I think original is 13 lb.

P.S. Also check the concentration of the coolant. Make sure it's -10 or better. If you have problems or do work to the truck, its easy for the concentration to get diluted. With the cold weather some places are having, it's easy for the radiator to turn into a block of ice and overheat the engine.

 

Thanks ...

The rad cap is only a few months old .. it looks OK

I "might" have found the problem ... the fluid was low, I thought because it boiled off (puddles and steam).

I found one very very small leak (more like a very slow drip).

I wonder if over the past few months it just got air into the system.

It took well over a gallon of fluid. I let it get all the bubbles out (even squeezed the top hose that is higher than the fill on the rad).

It idled for a long long time ... got warm but never near hot.

I will take it for a drive tomorrow and see what happens.

Maybe I got lucky ... just a dumb problem.

Thanks!

 

I’d beg, borrow, or steal a cooling system pressure tester. Pump up the system and make sure it can hold the rated pressure. Be sure to get an adapter to test the cap, too.

It’s quite possible to have leaks that don’t show up on an idle run. Not much pressure in the system at idle. A pressure tester will help find leaks you’d otherwise miss. Plus it’s a lot safer and you can do a better inspection without the fan and belts in motion.

 

Almost forgot - Test the seal between the radiator neck and cap. Details of my experience here:

https://www.ford-trucks.com/forums/1...lant-leak.html

 

If you let it idle till the upper radiator hose was hot and water was circulating in the the radiator (cap off) you should be good. If you didn't wait long enough, you may still have some air in the engine and that will have to work it's way out. You could have another episode.

 

From what I can tell had a similar issue with my 1994 f150 4.9. What I determined was my fan clutch went out and this solved my problem. How I was able to tell, when I started moving the air flow would cool the engine and if stopped and sitting for a while the temp gauge would rise and overflow and the fan had no resistance when turning.

 

Thanks so much!

I will test the system and see what is going on.

I was also wondering about the fan clutch.

Always something with a 37 year old truck ... still a daily driver (more fiberglass and body filler than metal) but the best $1000 I ever spent!

Thanks .... Mike