Is it common for the C7 3LT to have issues with the coolant cap? About 5 months ago my AC compressor took a dump and I had to put in a new one and with that part of it required me to disconnect the lower radiator hose and so I went ahead and flushed out the coolant system and then put in new coolant. I have a vacuum filler assembly that you put a special cap on and you use an air compressor to suck out the vacuum and get it to a negative reading and let it sit for 15 minutes or so to let you know if you have any leaks. And it didn't have any leaks, But I noticed over some time The car started running hotter and getting hot when I was sitting still at a red light. There's no air pockets in the engine or anything catching it causing me issue but one thing I noticed is the radiator cap or coolant cap I mean because it's not on the radiator The o-rings on it didn't feel like that they were seating into the reservoir, and so I noticed when I topped it off it was about a gallon short that there was like a pathway that went underneath it and dribbled out of the little hose on the bottom of the reservoir. Appears to be an overflow container or a excess pressure relief.
Anyways I am noticing that every time I park and I come out there is a puddle of coolant a small public coolant underneath my reservoir area. Is it common for the coolant caps to go bad? Or do I just need to get some new o-rings for the coolant cab and put them on? If so does anybody know what the size of the o-rings are so I don't have to go out measure it in try not to stretch out the o-rings anymore while I wait for a new ones?

Thanks in advance! She is my daily driver and I put just under a hundred miles a day on her. So driving out here in the Phoenix heat 100 miles a day I really need my coolant system to be perfect

 

I'd just replace the cap.

 

I agree with just replace the cap - not too expensive. And moving this to C7 Tech.

 

might have air bubble, cap may be ok!!

 

The overflow is low pressure, so don't think of it like a radiator cap. BUT I had a leak in the same spot and it ended up being the connection underneath the overflow container. You can't really see it unless you remove the container. It was an o-ring that I replaced and I've never had a problem since. I think I did a write up on here, and if I did I'll post the link.

I didn't really understand if you see it leaking from the cap or just the puddle on the ground, so if you see it leaking out of the cap, I'd ask is the level normal when cold and does the level then increase up to the cap when hot?

 

I do believe that the overflow bottle has a Pressure cap at ~ 15 lbs opening pressure. Just like the ones on the old style cars that did not have an overflow tanks.

First the radiators had the pressure capon them, then manufactures just added an overflow tank keeping the pressure cap on the radiator, then after a few years latter they moved the cap to the tank itself.

 

Thank you all for the replies! Yeah I'm just going to bite the bullet and start with the cap. I noticed that whenever I top it off and I run it with the cap off to allow any air to burp out, when I go to put the cap on while it's running it almost like it's got a pressure differential and it causes a valve underneath it to leak out on that side hose. I really hope it's not the container or the o-ring under the container that someone had pointed out on the thread. Not looking forward to having to remove it lol. So I'm going to start with the cap. I'll be ordering a new OEM one today and I will update if that fixes it.

Also to the mod, thank you for moving this to tech I wasn't sure if this was the proper place for it or not if tech performance was only for performance items and not standard maintenance items

 

There is only one way to check a Radiator Cap and that is have it pressure tested. You are just throwing parts at it. Bring the cap to a shop and have it tested.

 

I have replaced the cap, however the AC compressor just went bad so haven't been able to make sure that that would be issue as it was only one week after. I do have a pressure cap tester and the old one did test good but it was like $6 for a new cap so I just replaced anyways. The Phoenix is already been having our over 100° days And I'm replacing the AC compressor today so I can drive it again So fingers crossed and stays good. Otherwise if not the one person a couple threads above said that he had no ring in the bottom of the pressure sealer of the bottom of theb container that went bad where the little drain hose is on the bottom of it. So cat doesn't take care of it then I'll be pulling it down and taking a look at that. I may buy a new one just so it's nice and white and clean where my old one has turned that yellow plastic color. Lol

 

for $15, easy fix if it works!! if it doesn't, throw in the toolbox or giveaway at cars n coffee!!

2014-2024 Chevrolet Corvette Expansion Tank Cap - Dorman 54218CD - PartsGeek.com