Plastic Welding lawnmower fuel tank.

DuckyDave

Six Pointer
I am nearing my wits end trying to plastic weld a leaking black HDPE fuel tank on my Poulan 21inch self propelled model PR65Y21MA. This is a clamshell-type tank whereby the top 1/3 of the tank is apparently ultrasonic welded (or solvent cemented?) at the factory to the bottom 2/3 of tank. I got the mower used/free so am unsure how the first crack (3/8 inch vertical/perpendicular to the clamshell seam) developed. As I fixed the original crack I then noticed additional leaks along the factory weld. I am using a Harbor Freight plastic welder tool. I test for leaks by blowing my breath into the tank (fuel line attached to tank drain fitting) with cap in-place, spraying the outside of the tank with soapy water and then visually observing for bubbles. It seems no matter how I melt/move the welding rod/material, I "chase the leak" to another location. Whack-a-mole!!

On youtube (I know--be careful what you believe)I saw a guy whose technique seemed to make sense. First he melts at the leak location, then he adds material from the rod and "mushes around" the melted material at the leak location. Makes sense to me, but is there a better technique?

Also, is my soap bubble testing technique improper (too stringent, i.e. "false fails") for this problem? During my last failed test, there were 3 areas that produced bubbles. I filled the tank to the very top with water and sat the tank in a basin overnight. By morning there was approximately 1 Tablespoon of water in the basin, i.e. the tank leaked but very minimal. I could probably live with this minor leakage--just fill the tank to no more than 2/3 full before mowing, then if tank is filled slightly above 2/3 even with fuel "sloshing around" while mowing there should be little or no leakage/danger. Main caution would be to never store the mower with fuel above 2/3 level.

Any tips or suggestions for fixing this once-and-for-all?
 

pattersonj11

Old Mossy Horns
Chased the same issue last year....finally found a used tank that Didn’t leak from a repair shop.

I tried 3 times. As soon as one leak sealed, another would either be found or develop. My fourth attempt was just to coat the whole thing in the rubber spray off of tv, if it can work on that John boat, it can work on the tank....am I right?

I was wrong. Flex seal does not like gas. I suspected it would not, but tried anyway as. Last ditch effort.
 

bigten

Old Mossy Horns
Contributor
I'm not familiar with the welder you are referencing, but wonder if it is producing enough heat to release areas near the one you are repairing. I've had that happen when soldering radiators and also some delicate brazing situations. When repairing plastics, I use a beaver tail soldering tip on my solder gun and it seems to keep the heat more isolated to the repair spot. I normally use a correct color zip tie for fill material.
 

Eric Revo

Old Mossy Horns
Contributor
Most of the solvent resistant plastics don't take to welding that good..I'd buy a new tank off of Amazon and be done with it. That's what I did for a LawnMan push mower that I still have. I went ahead and bought the lines for it as well as all of that oxidizes at some point. Better to replace it all and be done with it.
 

HotSoup

Ten Pointer
Most of the solvent resistant plastics don't take to welding that good..I'd buy a new tank off of Amazon and be done with it. That's what I did for a LawnMan push mower that I still have. I went ahead and bought the lines for it as well as all of that oxidizes at some point. Better to replace it all and be done with it.
Best advice, especially if its had e10 aka pump ran through it
 

Buxndiverdux

Old Mossy Horns
I've never "welded" a solvent resistant tank. But I have plastic welded a few things successfully. I always use a heat gun to warm up the area before I start welding. Seems to work on sprayer tanks, headlight brackets, etc.
 

nontypical

Ten Pointer
I had a small leak on the plastic gas tank on my old generator. I found some stuff at oreilly's that was an epoxy that could seal up small gas leaks. Been up there for a few years with no problem. If its a bad leak I would do like woodmoose said and find a new replacement tank.
 

DuckyDave

Six Pointer
Thanks to all for the inputs.

Yes I have considered replacing the fuel tank. Thus far I have been unable to even determine a correct p/n for the tank. I have repaired dozens of mowers/blowers/trimmers/chainsaws/outboards/compressors/generators with both Used and New parts but this tank p/n eludes me. If you find the p/n I would love to know what it is. However, my guess on Price is in the $30-$40 range which approaches the Market Value of this mower (I want to resell it for at least $60-70. I need the "mad money" for more hunting and fishing stuff!)).

Thanks also for the tips (other than replacement) . I have already done some but not all of what you suggested. I will try again/differently .
 

Blackwater

Twelve Pointer
Get a tube of Seal-all at Dollar General for about three bucks, four bucks at Wal-Mart.. Used it on a welded seam in my string trimmer tank and she's still holding after 2 seasons. Applied it outside and inside. Inside I used a bamboo chopstick. A piece of bent wire with an eyelet on the end could be bent to reach where a straight tool won't.
 

Weaponologist

Four Pointer
I had a similar issue, However, I didn't try some of what's been suggested here. But trying close to what you did. My Mower tank would get wet in the leak spot by the time I finished mowing. I did as you said and just filled enough to get the job done with no extra fuel in the tank. I finally found a replacement that I could MAKE work. seems its very difficult to get a perfect replacement after a few years on a mower?? ..
 

DuckyDave

Six Pointer
I was able to sell the mower quickly for $80 and multiple Buyers wanted it. If I bought a new tank for it I would have had to price it around $120 to make the same profit I made "unfixed" at $80. I agree that after a couple years good replacement parts at a good price become scarce.
 
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