SOLVED! radiator cap stuck

[sunliner]

I thought I had seen it all with this truck. so it's been a while since I've opened the radiator but I tried tonight and I cannot get the cap to budge at all. about to put the channel lock pliers on it but I know this is a plastic radiator and I'd rather not snap the neck off. any tips n tricks to get the cap off without damage?

 

[Mooseman]

You able to push down on it while turning?

 

[sunliner]

You able to push down on it while turning?

No, but I don't think I ever did. Used to just screw off, slight resistance at first, but usually comes off pretty easily.

 

[Mooseman]

Maybe try to just try to turn it when it's hot. Maybe the heat can help break it loose. If that doesn't work, you might not have a choice but to use the pliers once cold.

 

[Reprise]

If the OP has access to a heat gun, that might be a better option than potentially voiding coolant, or scalding themselves.

I'd recommend keeping a flame away from the area, so that the plastic in either the cap or the rad doesn't melt / fuse together.

Some medium hammer taps on the top / sides of the cap may loosen things a bit.

And of course, push down a bit while turning. Might need to push down a bit firmly, vs the usual amount needed.

If all of that fails, and the channel locks crack the neck of the rad, some jb weld for plastics may repair it, at least in the short term. I used some on my headlamp housing the other day and it's still holding (although my headlamp is waaay out of alignment at the moment, and I need to see if I can re-aim it - if not, then the time spent trying to fix it will be for nothing)

Finally, it might be a good idea to have new cap on hand, especially if there's no backup transportation.
Good Luck!

 

[Mooseman]

Maybe I should have elaborated a bit more. Try to turn it while it's hot only to crack it open and not to completely open it. It takes a couple of turns to get it to be open and spew hot coolant. Just crack it open and wait for it to cool before opening it any further.

The heat gun is also a good suggestion. This plastic probably has a high melting point.

 

[Mektek]

I don't think you have to worry so much about using a large channel lock pliers on it. The Oring can be quite tight - unless you crazy glued it together you won't apply enough force to crack it before loosening it.

 

[TollKeeper]

Another option. When the engine is cold, get yourself a pot of BOILING water. And trickle poor it over the radiator cap. Just a thought

 

[Reprise]

Maybe I should have elaborated a bit more. Try to turn it while it's hot only to crack it open and not to completely open it. It takes a couple of turns to get it to be open and spew hot coolant. Just crack it open and wait for it to cool before opening it any further.

I know *you* meant this; I didn't qualify it further b/c I had to type that (and this) on my phone -- my laptop finally bit the dust yesterday. So no worries.

Hope you and everyone else on the site w/ covid is feeling better soon!

TL; DR -- OP, just exercise care if you try opening while hot. Which we're sure you know.

 

[sunliner]

thanks guys. so I got home after a short drive, sprayed a little WD40 around the edge , then after about 10 min, used the ol channel locks. hardly any effort at all and she came right loose. not sure what worked but it's behaving nicely. and no I did not spray a ton of WD on the cap. doubt any made it into the system plus this old battle axe has shrugged off worse abuse, Lol! but really , thanks again for all the tips. this is one of the most helpful forums I've ever been part of

 

[JayArr]

I know this is an old thread but I've been dealing with rad caps for a couple of days now and my experience is that when the rad is stinking hot the cap won't turn but if you are patient it will come off when it all cools down.

The cap is plastic with O-rings and I think when it's hot it actually expands to the point where the plastic cap contacts the plastic neck of the rad. When it cools down the only contact is the O-ring and then it comes off pretty easy.

HTH someone.

 

[paul2005tb]

GM is a pretty good manufacturer but some of the cheap solutions they do to save a penny by spending a dollar on a plastic redesign are discouraging, and the plastic radiator parts are one of them. There are places for plastics, but the radiator is not one of them.

Also, Im not sure it is the cause of the seized cap but Id recommend going with a 70/30 or even an 80/20 ratio of antifreeze/H20 if you are in a northern state. Unless you are stuck in traffic in 100F there really is nothing to be gained in a 50/50 mix. More antifreeze protects against corrosion.

 

[Mooseman]

Also, Im not sure it is the cause of the seized cap but Id recommend going with a 70/30 or even an 80/20 ratio of antifreeze/H20 if you are in a northern state. Unless you are stuck in traffic in 100F there really is nothing to be gained in a 50/50 mix. More antifreeze protects against corrosion.

Actually, the more antifreeze, the less efficient the system gets. Water is the best heat conductor. If we could, we would run straight water for the best heat dissipation but because it has poor lubricity and lower boiling point and higher freezing point, we have to add coolant/antifreeze. There's a reason why OEM use 50/50 as it is the best balance between cooling properties and freezing/boiling protection.

As per this article:

A 50/50 mixture of antifreeze and water is the standard recommendation for most applications because it provides the best all-round cooling protection and performance for most applications. Premixed antifreeze is 50/50 and takes the guesswork out of correctly mixing antifreeze and water. Most consumers find premixed antifreeze is much more convenient to use because it doesn’t require any mixing. A gallon jug also is less expensive than a gallon of straight antifreeze.


In some situations, the ratio of antifreeze in the coolant can be increased to as much as 70 percent. A 70/30 mix will lower the freezing point to -67 degrees F and to raise the boiling temperature to 235 degrees F. But a 70/30 mixture of antifreeze and water will not conduct heat as efficiently as a 50/50 mixture because the thermal capacity of antifreeze is not as high as water. That might cause the engine to run too hot and overheat if the cooling capacity of the radiator is marginal (which is often the case with many late-model vehicles that have relatively small radiators and cooling capacities).


Pressurizing the cooling system with a 8 to 15 PSI radiator cap will raise the boiling temperature of the coolant whether it is straight water or a standard antifreeze/water mixture. The cap seals the system and acts like a pressure cooker to prevent steam from forming. A 15 PSI cap can raise the boiling temperature as much as 45 degrees over an unpressurized system. But the cap pressure depends on the application and the strength of the radiator, heater core and other components. Replacement radiator caps should have the same pressure rating as the original on a stock cooling system.

And yes, our cooling system IS marginal so adding a higher ratio coolant mix will not help.

I run a 50/50 mix and do experience very cold temps (coldest I've ever seen is -36c) and never had any issues.

As for plastic caps getting stuck, I would rather recommend using a silicone based grease, like brake lube, on the cap threads and seal.

 

[paul2005tb]

Im not sure we are in disagreement, Yes more water gives you better heat transfer to the fluid but most of us are NOT driving in environments (ambient temperatures) where that is ever a concern. If you are driving in the northern states on highways you are not stressing your cooling system.

The other role of the antifreeze is anti-corrosion. Water is highly corrosive at high temperatures. And anti-corrosion is best with more antifreeze than water. I run 70/30.