Small leak out of the radiator cap?

[juggar]

Recently got my radiator replaced some months ago because it was puking out lots of coolant. Mechanic said that yes, there was a leak.

Ever since I got the new radiator in, it seems to leak out of the cap. It stopped leaking once the coolant level got low enough in radiator. Like a quart low, thats what I had to put in to bring the coolant level right to the cap neck.

When I put the quart of coolant in, I also put on a new motorcraft radiator cap as the previous cap was being reused and I thought it might have been going bad.

Well, it seems to trickle coolant out of the cap once the truck is warmed up for whatever reason.

Any ideas? Could exhaust gas be pressurizing the coolant? ( aka head gasket leak?) There is absolutely no smoke coming out of the tailpipe so I know its not burning coolant. The coolant reservoir does not seem to fluctuate in level, but I ran compressed air through the hose that goes to it so I know its not plugged up as the air quickly bubbled up in the reservoir.

I really have no idea why in the world it would leak out the cap and not just go into the reservoir....

 

[koda2000]

Whatever is going on it should never leak from around/under the cap. Remove the overflow hose and check it for any cracks, also blow through it to make sure it is not clogged. If the hose is ok and clear, check the sealing surface on the radiator, under the cap, to make sure it's smooth and that there are no irregular surfaces or cracks there. With a new rad and cap there should not be any leaks.

It is possible that a blown head gasket will allow exhaust gases into the cooling system and not let coolant into the combustion chamber or oil, but that would cause bubbles in the coolant overflow tank, not leaking from under the cap.

 

[juggar]

Whatever is going on it should never leak from around/under the cap. Remove the overflow hose and check it for any cracks, also blow through it to make sure it is not clogged. If the hose is ok and clear, check the sealing surface on the radiator, under the cap, to make sure it's smooth and that there are no irregular surfaces or cracks there. With a new rad and cap there should not be any leaks.

It is possible that a blown head gasket will allow exhaust gases into the cooling system and not let coolant into the combustion chamber or oil, but that would cause bubbles in the coolant overflow tank, not leaking from under the cap.

Yeah, the rubber tube to the tank should be OK as I did attach it to a can of air and it bubbled up in the reservoir. Guess I could replace it for the hell of it though, it is 18 years old.

I think I will take the cap off and check the sealing surface though, It was an $80 radiator from eBay so probably not the highest quality. I had to zip tie the rubber overflow tank tube to the damn nipple connection on the neck of the radiator as it literally was just sitting there ready to fall off. Not sure how they let it leave the shop like that, I figure that rubber tube and connection has to hold some kind of pressure.

 

[RandomNerd2000]

I'd check your cap surface/area closely, my 99 was having the same thing when I bought it, except it was a quart low, so I filled it and hit the road for a store two miles up the road, needlessly to say, not an inviting experience.

 

[koda2000]

Yeah, the rubber tube to the tank should be OK as I did attach it to a can of air and it bubbled up in the reservoir. Guess I could replace it for the hell of it though, it is 18 years old.

I think I will take the cap off and check the sealing surface though, It was an $80 radiator from eBay so probably not the highest quality. I had to zip tie the rubber overflow tank tube to the damn nipple connection on the neck of the radiator as it literally was just sitting there ready to fall off. Not sure how they let it leave the shop like that, I figure that rubber tube and connection has to hold some kind of pressure.

The rubber tube must fit tightly on the nipple of the radiator neck. The cooling system is a "closed system" in that the coolant flows into (and back out of) the overflow tank/reservoir. If there's any question about the hose, replace it. Also check the sealing surface for the cap.

As far as the shop letting it leave with a bad hose connection... that's why I do my own repairs. In the rare even something is not done properly, I have no one to blame but myself.

 

[juggar]

Well, I found the reason!

Upon further inspection today I found that the rubber gasket/washer that was sitting below the cap was not supposed to be there. The cap already has one.

No wonder the cap would hardly fit! Now it fits like a glove on the radiator neck without having to use a huge amount of force to get it on.

It was confirmed by the fact that this extra gasket was fully blocking the small hole that led to the nipple for the overflow tank hose! So thats why the overflow tank was not being used.

No more leaking out of the cap now.... it leaked a very small amount out of where the hose meets the nipple but I can probably find something better than a zip tie to fix the hose to the nipple.

Now I pray my radiator is OK after being subjected to that abuse, looked like there could have been another leak but maybe that was just residual from the leak out of the cap pooled down at the bottom.

Now my shop is pretty good to me so im going to just chalk this up to a one time screw up.

 

[koda2000]

Well, I found the reason!

Upon further inspection today I found that the rubber gasket/washer that was sitting below the cap was not supposed to be there. The cap already has one.

No wonder the cap would hardly fit! Now it fits like a glove on the radiator neck without having to use a huge amount of force to get it on.

It was confirmed by the fact that this extra gasket was fully blocking the small hole that led to the nipple for the overflow tank hose! So thats why the overflow tank was not being used.

No more leaking out of the cap now.... it leaked a very small amount out of where the hose meets the nipple but I can probably find something better than a zip tie to fix the hose to the nipple.

Now I pray my radiator is OK after being subjected to that abuse, looked like there could have been another leak but maybe that was just residual from the leak out of the cap pooled down at the bottom.

Now my shop is pretty good to me so im going to just chalk this up to a one time screw up.

Glad you found the problem and seem to have it straightened out.