old radiator cap leaks, replaced, new one leaks occasionally

[sashainwy]

The old one leaked, and the rubber o-ring thing was flattened. I replaced with new ACDelco, the rubber o-ring was nice and round. Still get intermittent weeping. I shot these after driving into town and returning. I barely smelled coolant when I got out of the car and shot these pics.

I did read somewhere a guy had multiple new caps, and they all leaked, and he doubled up on the rubber gasket/o-ring I think, and that stopped it.

Is it possible to over tighten by hand? It's a very strange cap, maybe all modern ones are like it. I'm used to the old school, where there's a stopping point... I guess those old school are metal caps and metal tops.

 

[Mooseman]

Dis you check the radiator neck for any cracks or damage?

 

[sashainwy]

I think I'm overfilled. I didn't think overfilling the radiator was possible if one had a decent amount of space still left in the overflow reservoir, but that might be only true of my old trucks. When I pull the cap off, it's filled all the way to the very top. I'm gonna double check the overflow, make sure I'm in the right range, and then remove some coolant from the radiator to get the level to maybe an 1.5 inches below the neck.

 

[Mooseman]

Once the cap is on and all spillage is mopped up or blown out, it should no longer leak.

 

[TequilaWarrior]

I recently installed a new cap because my old one was leaking (flattened o-ring as well). I had some weeping for the first few drive cycles but it eventually stopped.

 

[sashainwy]

I looked at it again. So now I noticed after I wiped off some crud, I can read the overflow tank. I always thought "full cold" was some where in the middle of the tank judging by the text. And there was some "other" text I couldn't read at a glance, till now. I figured that "other" text was something about minimum fill, because it pretty much pointed to nearly empty from that point of view.

I would have never guessed that "full cold" or in my words "max fill cold" would be almost empty. Anyway, I was at just over half the tank at cold so I siphoned out coolant till I was just under the "full cold" mark, the real one. I also removed a tad from the radiator so it wasn't filled right to the tippy top of the cap neck.

I also cut 3/4 of an inch from the overflow hose/line at the radiator end, so that it fit tight again.

Not sure if it'll make a difference or not. We'll see.

Upper green line is where I thought "full cold" was, didn't learn till recently the actual "full cold" is the lower green mark. "PLEIN A FROID" is french for full cold.

 

[sashainwy]

Still weeping. Had zero impact on coolant levels, it's such a small amount, but it's annoying. Went to Ace Hardware, where they have 4 boxes of different sized o-rings.

Found a prospective fatter replacement for the larger diameter o-ring. Could not find a good candidate to replace the smaller diameter o-ring, so I also bought skinny ones to supplement by installing first, then installing the thick ones on top. Basically doubling up.

Initially doubled up both large and small diameter o-rings, but subsequently removed the double up for the larger o-ring. Cap doesn't screw on quite as far, but plenty. Not a single drop.




Makes life easier.


dry as can be

 

[mrrsm]

Unfortunately, when it comes to issues with ALL Automotive Radiators... Even the MOST Experienced Mechanics either fail to possess any decent Coolant System Pressure Testing Equipment... or if they DO... They simply Do NOT Know How To Properly Use The Kits.

Right Now... You can find Old, Chrome Plated ACDelco, Snap-On (Blue Point) and Stant Coolant Pressure Test Kits that will range from around $110.00 down to much less $$$ for the incomplete or well used kits:

Stant Cooling System Pressure Tester ST270-12270 in Case for sale | eBay

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I picked up THIS Kit for $14.00 + S&H via eBay just now...



THIS is what the Brand New Stant Coolant Pressure Testing Kits SHOULD Look Like:

Stant Cooling System Tester, Metallic | eBay

Pressurizes up to 30 system/cap.

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Stant has a Special Coolant Tester Adapter specific for the Trailblazer-Envoys 4.2L Engine Radiators available from ROCKAUTO for Only $20.00:

2002 CHEVROLET TRAILBLAZER 4.2L L6 Cooling System Tester Adapter | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

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...and for the Chevrolet-GMC GMT800 V8s:

2002 CHEVROLET SILVERADO 1500 5.3L V8 Cooling System Tester Adapter | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

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Follow along with THESE Dudes and you'll get the feeling in most MOST Coolant or Radiator Leak Threads investigating issues with Coolant Loss, you won't find any mention of "Actually Testing The Radiator Cap" with the Proper Tools ... AND... By Using the Proper Methods. You should find the Videos from THESE Dudes very "On Topic" ...and really quite interesting:

Stant Coolant Pressure Tester Procedures:

Checking Your Radiator Cap for Pressure Relief:

Performing a Coolant Leak Pressure Testing on a Chevrolet Silverado:

 

[mrrsm]

I already have the Snap-On Blue-Point Coolant Tester Kit Model #SVT-262 for testing Pressure Caps and Coolant Systems on Large Trucks. But this STANT Kit was much more Up To Date ...and as a Base Kit... I could NOT Pass It UP as it was ONLY $14.00 over on eBay... PLUS S&H.

The Green Adapter depicted in these images (from a separate purchase) Fits my 2000 Chevrolet Silverado Radiator and the Adapters included allow for Testing the Cap Under Pressure using the "5 Gallon Bucket of Water Dunk for Air Bubbles" Method outlined in the previous Videos:



Just take a minute ti look over THIS Dude's Shoulder and observe just how Simple and Useful having a Tool like this can be:

 

[mrrsm]

If you decide to research getting the STANT Model #12270 Coolant Tester Kit ***USED*** Via eBay... You might have some concerns about its "Shop-Wear" and perhaps NOT Sealing after it being used in so many repairs over the decades. Fair Enough...

BUT... Guess What?

The STANT Coolant Tester ***REBUILD*** Kit is available from both Amazon On Sale for around $6.00 ...AND it's available over on eBay (for under $10.00).


Available at Amazon...

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And… Available at eBay...

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=Stant+12703+Head+Repair+Kit+for+(12270)+Cooling+System+Testor+&_sacat=0

 

[mrrsm]

As a Final *Piece* in the STANT Coolant Tester Kit *Puzzle*... The attached Images show what the Kit looks like after rebuilding the Locking Head with that aforementioned $6.00 Kit and after disassembling the Compression Cylinder, cleaning out the Inner Hard Chromed Tube with 2-3 Brillo Pads to remove the Rust and flush out all of the Old Detritus inside and then applying Food Grade Silicon Grease to the Leather Plunger Pad that seals it up and allows for a VERY Smooth Plunger Operation.

The added items here are the Radiator Cap for the 2000 Chevrolet Silverado 1500 5.3L and its particular Green Tester Adapter for Pressure Testing when the Head is submerged inside of a Bucket of Cold Water. EVERYTHING Fits NICELY inside of the STANT Carry Case when the Tester Work is finally done! I LIKE This!

 

[gmcman]

Still weeping. Had zero impact on coolant levels, it's such a small amount, but it's annoying. Went to Ace Hardware, where they have 4 boxes of different sized o-rings.

Found a prospective fatter replacement for the larger diameter o-ring. Could not find a good candidate to replace the smaller diameter o-ring, so I also bought skinny ones to supplement by installing first, then installing the thick ones on top. Basically doubling up.

Initially doubled up both large and small diameter o-rings, but subsequently removed the double up for the larger o-ring. Cap doesn't screw on quite as far, but plenty. Not a single drop.

View attachment 108453


Makes life easier.
View attachment 108452

dry as can be
View attachment 108454

Can you provide a link or description of the o ring you purchased?

 

[sashainwy]

Can you provide a link or description of the o ring you purchased?

I just drove to Ace Hardware with a brand new cap in my hand, and bought a half dozen o-rings that were "close" in size.

Now is probably a good time to mention that even with three, new, "oe" (supposedly) caps, I still would have a drop or three of seepage, when I would park and check under the hood. Even with o-ring mods.

I figured that a massive batch was made wrong, or my radiator opening was stretched, or some other alignment of the sun/moon/stars was happening.

So I figured it might be worth trying a non-oe cap (since the design might actually be different), and I picked up a motorad brand from local parts store, and it did indeed have a slightly different design compared to the other 3. I still swapped out the o-ring (one closest to where you grip the cap to screw it on) on this new motorad cap with the thicker one from Ace Hardware. This combo is the one that has worked for months. No more coolant smell, and no more drops weeping.

You'll just need to experiment is my guess.