Question about overflow tank

[GSTwithPSI]

I recently swapped in a new DSM style radiator that's a sealed type rather than one with a radiator cap. As a result, I had to also swap in a DSM style water neck with the provision for the radiator cap. Ever since I did the swap, the radiator cap seems to be working funny.

As the car heats up, the coolant expands and the cap lets coolant bypass into the overflow tank as it should. I can visually see the fluid level rise. However, the cap is not allowing coolant to return to the cooling system as the car cools. If I shut the car down and let it sit, the coolant level in the overflow reservoir stays the same, even if the car sits overnight. What's really crazy is that if I take the radiator cap off the next day, it literally pops and I can hear the vacuum that built up in the system overnight release. This should be the vacuum/negative pressure/whatever, that draws the coolant back into the system from the reservoir tank, but it's not doing its job.

The system obviously holds pressure and is leak free. Aside from the scenario above confirming that, I pressure checked the system up to 20 psi...Good to go. I've tried 3 radiator caps: a 13lb Stant cap, a Mishimoto 19lb cap, and also a Greddy 1.4 bar cap. Same deal with each cap. The T-stat is new, and the system functions fine aside from this issue.

Ideas /ubbthreads/images/graemlins/dunno.gif

 

[transparentdsm]

So you know the tube that sits inside the overflow, check it for cracks and make sure its sealed to the lid properly. Maybe it's leaking back in the overflow and can't return to the system.

 

[GSTwithPSI]

Good call, Shane. I'll give that a look. I know the tube is there, but I should take a closer look to make sure it's not screwed up. Thanks.

 

[prove_it]

Even without the tube hooked up the block would pull air back, and not hold vacuum.

Sounds like the cap isn't functioning properly to me. Either the wrong cap, or defective.

 

[prove_it]

Sounds gross to do, but pull you hose off the thermostat housing and make sure you can suck coolant through it. Could have a funky hose that's acting like a one way valve too.

I.E. the hose collapses under vacuum and won't allow coolant flow, but under pressure (venting coolant) the hose allows flow.


My only two ideas sir, cap or hose issue.

 

[FlyingEagle]

"I recently swapped in a new DSM style radiator"

Any possibility the depth of the fitting for the rad cap is different between the old rad and the new one, causing a flow impedance.

 

[prove_it]

Could be from not controlling your fans with link too.

 

[iceman69510]

Lol at Ryan. /ubbthreads/images/graemlins/rofl.gif

 

[turbowop]

Quoting prove_it:
Could be from not controlling your fans with link too.



Srsly /ubbthreads/images/graemlins/wink.gif

 

[GSTwithPSI]

So, dicked with this some today. For some reason, the radiator cap vacuum valve isn't relieving pressure. I believe it has something to do with my water neck. It's almost as if the neck is too shallow, and it's somehow impeding the vacuum valve's ability to release. I compared the depth measurement of the 1G water neck to the radiator on 820, and the 1G water neck is a bit more shallow. I'm wondering if this water neck is from another car or something? Is there a Hyundai water neck or some sh*t that closely resembles the 1G water neck?

For testing, I put the radiator cap on 1837, and tried to blow air back through the overflow hose. I couldn't get any air through. I took the same cap, and put it on 820, and performed the same test. Air bypassed the cap freely. I tried this with 2 separate caps with the same results.

I ordered a new 1G water neck from STM, which I'm hoping will correct the issue.

 

[FlyingEagle]

I hope that solves it for you!

Nothing ticks me off more than parts imcompatibilities and JSB status when this occurs. /ubbthreads/images/graemlins/cool.gif

 

[tektic]

I have issues with a brand new Stant rad caps with same setup. I have some junk rad cap on there now and it works better. I'm going to inspect it more closely now.

 

[prove_it]

The dsm caps and GVR4 caps are supposed to the be the same right? Rounded ears on the cap, not pointed right?

 

[transparentdsm]

ok so here is a thought, is there a difference from the 90 coolant neck and the 91 - up?? i know 90 DSM's have a lot of different parts then the 91 - up's

 

[tektic]

I don't think so, but. I have a few defenetly one of each. I can measure on Wednesday.

 

[Coltsfan]

There are two different sized (Japanese) radiator caps. One is deeper than the other. Often times when you get an aftermarket radiator, the cap style will vary, but I doubt the water outlet is different/odd.

 

[tektic]

I found it...

No updates though /ubbthreads/images/graemlins/frown.gif

I'm using the dsm rad and neck and overflow is not working either way. I develop leaks and system remains pressureized for days after engine has been run. This has been multiple caps.

 

[GSTwithPSI]

My issue ended up being the water neck. For whatever reason, I swapped in the new water neck and everything started working like it should. There's a tiny little lip on the top edge of the DSM water neck. Mine was worn out, which affected how the relief ports on the radiator cap were able to function. I can take some pictures of my old one and post them up if that helps.

 

[tektic]

Pics may not be necessary. I'll inspect mine. I'm just looking to see if its still square? Not pitted?

 

[citymunky]

In for pics.