I bought an '88 F150 with the 4.9L I6 engine about 3 months ago.

When I bought it the previous owner told me he has started smelling antifreeze and something had just started squealing under the hood and it was probably the water pump. So after I bought it I replaced the water pump and all was well.

Then a month ago the radiator was rubbing against the A/C condenser, so I had the hole in the radiator patched and didnt really drive it for a month.

Today I drive it some and notice that Im down on coolant after I get back, and Im pretty sure its all coming out the vent tube. What would cause that? I had to add a gallon to get it back up to the top of the radiator.

I appreciate any help I can get, thanks.

(Oh and the temp gauge on the dash is broken)

 

Some of the radiators had one tube going to the overflow and another one going toward a split on the heater hoses. Most probably only have the tube to the overflow. So, do what everybody else does and try to find a vacuum line cap and put it on the nipple where the coolant is leaking from. Your problem should be fixed for good. (all the others I am aware of with this problem are).

As for why this happens... Thats what happens when the water gets hot and normally it would run to the overflow and then be pulled back into the radiator when its cool. But instead it is leaking out the opening.

 

Thank you for your reply.

(And bear in mind I am NOT and mechanic)

This truck has a small line that runs from the coolant tank, over the plastic fan shied, and then into the radiator on the passenger side.

There is also (what I assume) is the little bit larger vent line on the passenger side that just points down toward the ground, and this is where coolant is coming from. You're saying I should plug the vent line?

Wouldnt it over pressurize the system?

 

The other vent line is up by the filler neck, correct? (thats where it should be)

No, it wont over pressurize the system for two reasons: 1. your cap will open up if its working properly to release the pressure because the caps are made with a crack pressure to prevent the buildup if it becomes an issue and 2. the coolant will flow into the overflow. It is just finding the first path it sees which is out onto the ground. Its a path of least resistance scenario.

 

Ok, thank you very much sir! Ill try it.

This will probably be the first of many questions on this truck, lol.

 

Usually when it come out the safety vent it usually means a weak or defective radiator cap...

vent pointed at ground for safety.

 

Ok, I could try a new rad. cap, thanks!

Any other ideas?

 

I fixed one like that with a new cap. Do that and report back.

 

Buy a Motocraft cap.

Also, relating to fluid coming out the vent tube to the overflow tank. If that is what is happening, chances are, head gasket isn't far to go. It is allowing exhaust gases to force air back thru the cooling system, and as Volvo92906 stated, least resistance.

If I misinterpreted the post, hopefully it's just a bad cap.

Do report back on your results.

 

If the cap fixes it, good deal. If not, worst case scenario: head gasket leak- leaking compression into the cooling system which overpressurizes the relief valve in the radiator cap. Cross fingers it's just a weak cap.

 

Thank you for the extra replies.

I talked to a mechanic I know and he brought up that it might be a cracked head or gasket. He suggested making sure the radiator is topped off and looking down into it with the cap off and watching for air bubbles. (from a cold start) So Ill look at that first and hopefully determine what the problem is.

 

If there's a bunch of crap on the bottom of the cap, it could inhibit some of the moving/sealing parts of the cap from working properly. Try cleaning it off and check the edge of the negative pressure valve, clean it with a fingernail and make sure it can seat properly, sometimes it can get stuck open by debris. It is designed to let flow return to the radiator, in but not out (unless it sticks open). You can lift it up slightly and see if the edges are able to seal well.

 

Ok today I finally had some time so I made sure the radiator was topped off and started the truck and looked down into the radiator looking for any air bubbles that might indicate a cracked head/gasket and thankfully never saw any.

Then I got to looking and I just couldnt figure out for the life of me why the vent hose was attached to the radiator under the return to tank line, so I reversed them so the return is under the vent. Then I drove it for 30 miles and I dont think I lost a drop. Im not sure if thats the final answer or the "correct" thing to do, but it seemed to work.