Fishnaked

Yesterday, after driving my truck on a rough dirt road at 5-15 MPH for 5 miles, I shut it off and heard what sounded like boiling water. I popped the hood to find coolant boiling out of the coolant recovery tank. The lid never fully popped off but there was enough pressure that coolant was finding its way out.

It was hot out... mid 90's... and I did climb a hill just before shutting it off. But......the hill only climbed 140' in 1/4 mile... so not that steep... and I didn't have much weight in the back, and I was only going ~10 MPH. I've climbed this 100 times in this truck, no problem. I did not get a look at the temp gauge.... but, I think, if it were that hot, I would have noticed. At least I'd like to think so...

The truck did the same thing last year when my wife was driving it. It was in the 80's but the truck did have weight in the back (about 400-500 pounds) and she was driving up a steep mountain pass for about 4 miles at ~50 MPH, with the AC on.

I put a new radiator in 3-4 years ago. I checked the coolant before leaving yesterday. It was good.

Anyone have any idea as to what's going on?

PerryB

Make sure the rad. isn't externally plugged with bugs and dirt. Blow/wash it out thoroughly. I'm thinking you probably need a new fan clutch though.

Fishnaked

Thanks. How does one tell if the fan clutch is bad? Any other possibilities?

PerryB

When cold the fan should be fairly hard to turn. When the engine is hot you should hear a good whoosh when the rpms are up. Its somewhat ****er-intuitive because it'll be engaged upon cold start, drop out after 30-60 sec. and then re-engage hot as needed. My son's truck was recently running hotter than normal at lower speeds (not to the degree as yours) and on an educated guess we threw a fan clutch at it -- genuine Motorcraft -- and it came back to normal.
FWIW we also put a 12" electric pusher fan in front and tied it to the a/c clutch wire via a relay (took the power itself off the battery). Now whenever the a/c is engaged there's much better airflow through the condenser and radiator. Low speed a/c performance and temperatures are noticeably better.

PerryB

The other likely candidate is the thermostat not opening completely. The last possibility is ugly......head gaskets.

SaltEater

Just to be clear, you did check all the cheap/easy stuff right? No collapsed hoses, rad cap is in good shape?

Fishnaked

Thanks, guys! I just went outside and checked the radiator. There are bugs, including butterflies, on it. However, I don't think there are enough to cause an issue. Regardless, I will clean them off.

I checked the fan. With the engine off and cold, I can spin it 1/8 to 1/4 of a turn... with some effort.

As far as the cap and hoses.... I did not think to check for collapsed hoses when the problem arose the other day. But, upon just looking at them, engine cold, I could see nothing obviously wrong with them. I took the cap off... and though I don't know how to tell if it is in good shape or not, I could see nothing obviously wrong with it. It fits and looks good.

One thing I didn't state in my original post is that this truck only has 80,000 miles on it.

So, with all that said... does that help narrow it down? Does the fan sound like it's ok... or would a problem with it not be that obvious? Should I reason that the thermostat is the most likely culprit and replace it?

SaltEater

The rad cap will have a few seals and a plunger in it, as long as the seals don't look ragged or fouled with dirt/scale and the spring isn't weak it should be ok. You can pressure test it also. It should hold something like 12-16 psi of pressure, if it's not holding it can let hot pressurized coolant into the puke tank (earlier than it's supposed to) which will boil off in open air. It can also let air into the system, allowing coolant to boil in the system which can create an overheating situation. The pressure differentials can cause hoses to go egg shaped or collapse when it starts cooling off too.

Why did you change the rad in the first place? Did you put the same size rad (or bigger) than you took out? 80 000 miles is not a whole lot for this age of truck, was it sitting for quite some time? Did you have to add a fair amount of fluid to the rad recently? Is it possible there is air in the system somewhere?

A thermostat is another super cheap part to replace, can't really think of a way to test it without making a mess. I guess if you do go that route and it's still a problem the next thing would be the fan or waterpump.

Fishnaked

Thanks! I'll take my cap to the local radiator shop and have it tested.

I changed the radiator as the old one had a leak in an area the radiator guy said could not be fixed. The new radiator was the same size as the old one.

Should not have had air in the system. I spent a lot of time figuring that out and getting the thing topped off one year ago. I have not had to add any since, and I check it often.

I'm the third owner of this truck. The original owner just didn't drive it that much... though may have let it sit a bit in his later yrs. The second owner put some miles on it. Finally, for me, it is not a daily driver. I drive it less than 5000 miles per year.

Steve83

What truck? You haven't told us anything about it, besides it having a 3-y.o. radiator. Click this, read the caption, and put ALL the truck's details into your signature:


(phone app link)How old is the radiator cap, and has it been pressure-tested recently?


(phone app link)How exactly did you check it? With a specific-gravity meter? Chemical test strips?The TSB in this caption explains exactly how:


(phone app link)Thousands. But you have to narrow them down for us by filling in your signature.