I installed an aluminum coolant expansion tank off of Amazon a couple months ago. I had issues with the coolant dribbling out of the overflow nozzle on the tank, very similar to the issue another person was having here: https://www.northamericanmotoring.co...-question.html

No matter how low I kept the coolant level, even when it's 1 inch off the bottom, it ends up dribbling out over a few hours of driving. Eventually, I ended up blocking the overflow nozzle off with a vacuum cap. I've driven with it like that for 12k miles with no cooling issues, but when I pulled the front end off to replace my alternator, I noticed my coolant hoses were flat until I opened the cap, so there's definitely no venting going on from the cap that came with the tank.

What are the long term consequences of driving like this? The reason I blocked it off is because I worry that the car will eventually run low on coolant on longer drives. Any suggestions? Or should I leave it blocked off? Did I maybe bleed the system poorly?

 

It sounds a lot like a bad radiator cap to me (or maybe a tank that just doesn’t seal properly to the cap?) since it’s apparently venting coolant at levels and pressures it shouldn’t. The vacuum cap you put over the vent probably vents pressure but then doesn’t allow the system to equalize as it cools, hence the collapsed hoses.

Oh. But you said no cooling issues… hmm. Well, I still suspect your flat hoses are from the vacuum cap not allowing the system to equalize. Maybe the cap opens at too low of a pressure but is still somewhat functional?

 

I don't think the radiator cap is supposed to vent on this tank? It seems like the tank was supposed to vent through the overflow nozzle but has not since I blocked it off. The tank has been holding coolant since and not coming from the cap or anywhere else. I'm just wondering the consequences of this since the flat hoses are kind of concerning to me.

 

Expansion tanks require pressure-rated caps that can vent to the atmosphere. Wait. You do have a normal radiator cap on it, right?

Is the vacuum cap just pushed on, or is it hose-clamped on?

 

This is what it looks like, it's the cap that came with the tank I bought. I stand corrected, looks like it's designed to vent?

Also the vacuum cap is just pushed on. No hose clamp. Figured I'd want it to pop off if pressure got too high.

 

The tank is intended to be pressurized in that system (R53, right? The R50 has a simple recovery tank), so it has to be able to vent. I’m still betting that the vacuum cap is venting pressure even though it hasn’t popped off. Then as the system cools, the vacuum cap seals, giving you a vacuum in the system and collapsing your hoses.

Obviously I’m guessing, but this is the best explanation I can come up with at the moment.

 

Yup, R53. Are the collapsing hoses a concern though?

 

Collapsed hoses aren’t exactly a good sign and probably not great for the hoses long-term. Are you sure you aren’t boiling your coolant, i.e. have you checked the actual coolant temp? The gauge in the center cluster sits right in the middle over a fairly large range (though I don’t recall what the upper end is, if I ever even knew). That would explain coolant loss even with very little in the tank.

I’m highly suspicious of that radiator (expansion tank) cap since you really shouldn’t have been consistently pushing coolant out of the vent that you capped off. It should stabilize at a level and stay there. I guess there could be other reasons besides a bad pressure cap, but I’m not convinced that something wonky isn’t going on.

 

Well I guess I'll just replace the cap with something proper and known thats rated to 16 psi for peace of mind and go from there. I haven't checked the coolant temperatures. I'll go on a drive tonight and check, but yes that gauge always stays centered.

The radiator hoses are also probably really old though. I'm not sure they've ever been changed.

 

Just checked, coolant temps are ok. Sits at about 190 on the freeway going 80-85.

 

Yep, most likely the cap. I have seen those amazon and ebay brands fail on a lot of stuff. They can also get pin holes in the bad welds.

 

Think you nailed it.

 

Thanks guys, I'll replace the cap and if the hoses are still collapsing after that I'll replace them as well. I'll leave the overflow vent plugged. Hopefully this solves my issue.

 

Glad the temps are okay. I was hoping that was the case since you didn’t seem to have any other issues.

I hope we’re right about the cap, but it seems like the simplest explanation.