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2022 Hisun Sector 750- Oil drain plug leaking


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My drain plug is leaking at a slow pace but enough to be leaving oil on floor. Talk to dealer and I replaced o-ring and checked mating surfaces and all good. Still leaking but at a slower pace. Now dealer is calling Hisun to see what’s up. I’m thinking the recess in the drain plug was cut to deep and when installing o-ring it just doesn’t seem to leave enough rubber above the flush/crush portion of sealing surface. Maybe a defective drain plug, that would be my guess. Wondering if anyone has had this issue with there’s. Dealer said this is a first for him. Waiting on reply from dealer.

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Not sure on that one.

My UT400 has a copper crush washer on the bolt rather than an O-ring.

Can you try putting just the o-ring (no bolt) in the groove and see how much it sticks up past the face. IIRC orings are supposed to compress 30-40% for proper sealing. So it should stick 30%-40% of its thickness past the face. If it doesn't you could try a thicker o-ring with the same diameter.

They are sold in diameter as well as material thickness so you should be able to measure and order one. Keep in mind it is probably metric. Grainger is a good place to buy random weird size metric o-rings in my experience.

Edit: had one other random thought. I had a plug on my oil tanker that was a perpetual leader. It was gaskets internally. Anyway long story short after much frustration the issue was the hole was not tapped perpendicular with the deck it was going thru causing it to never seal tightly on both sides.

I wonder if your drain plug is tapped slightly crooked causing it to not seal on one side when the other side is tight?

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10 minutes ago, aefron88 said:

Not sure on that one.

My UT400 has a copper crush washer on the bolt rather than an O-ring.

Can you try putting just the o-ring (no bolt) in the groove and see how much it sticks up past the face. IIRC orings are supposed to compress 30-40% for proper sealing. So it should stick 30%-40% of its thickness past the face. If it doesn't you could try a thicker o-ring with the same diameter.

They are sold in diameter as well as material thickness so you should be able to measure and order one. Keep in mind it is probably metric. Grainger is a good place to buy random weird size metric o-rings in my experience.

Edit: had one other random thought. I had a plug on my oil tanker that was a perpetual leader. It was gaskets internally. Anyway long story short after much frustration the issue was the hole was not tapped perpendicular with the deck it was going thru causing it to never seal tightly on both sides.

I wonder if your drain plug is tapped slightly crooked causing it to not seal on one side when the other side is tight?

I’m thinking I’m only getting a 20% crush. That’s why I’m thinking that the drain plug groove was machined to deep preventing the proper crush. Will see what the dealer says. I’d rather get a new drain plug instead of bastard sizing with thicker o-ring. If that’s even what it is. Thanks for jumping in on this.

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On 8/10/2022 at 7:45 AM, aefron88 said:

Not sure on that one.

My UT400 has a copper crush washer on the bolt rather than an O-ring.

Can you try putting just the o-ring (no bolt) in the groove and see how much it sticks up past the face. IIRC orings are supposed to compress 30-40% for proper sealing. So it should stick 30%-40% of its thickness past the face. If it doesn't you could try a thicker o-ring with the same diameter.

They are sold in diameter as well as material thickness so you should be able to measure and order one. Keep in mind it is probably metric. Grainger is a good place to buy random weird size metric o-rings in my experience.

Edit: had one other random thought. I had a plug on my oil tanker that was a perpetual leader. It was gaskets internally. Anyway long story short after much frustration the issue was the hole was not tapped perpendicular with the deck it was going thru causing it to never seal tightly on both sides.

I wonder if your drain plug is tapped slightly crooked causing it to not seal on one side when the other side is tight?

Dealer is getting a new drain plug with matched Oring to go with it. I’m curious to see how deep the groove is on the new plug. Hopefully there will be a difference so I know I found the root cause, will see

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  • 2 weeks later...
On 8/12/2022 at 8:20 PM, Roadstar515 said:

Dealer is getting a new drain plug with matched Oring to go with it. I’m curious to see how deep the groove is on the new plug. Hopefully there will be a difference so I know I found the root cause, will see

Well got new drain plug and oring and looks identical to original and same crush distance. So what I did was Teflon taped threads being carful not to have any excess that would enter oil reservoir. Even though there is a strainer which would prevent that. Anyway, problem solved but would have liked to know why that was leaking in the first place. I still say it didn’t have enough crush to properly seal it the correct way as designed. I don’t like fixing symptoms, I’d rather fix root cause.

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It's unlikely that the teflon tape did anything useful. Teflon tape doesnt seal, and almost every pipe dope sold dosent seal either (there are a few specialty exceptions).

The concept of teflon tape is that it allows the threads to slide more easily. It is only needed in a tapered fitting. In a tapered fitting, such as NPT the further you thread the fittings together, the tighter the seal. This is why you use teflon/dope on say piping in your house.

The drain plug bolt, in this case, is a straight thread so tightening further doesnt cause the threads to seal any tighter. This is why the o-ring is there in the first place. The o-ring is the only thing that really seals, as oil can seep right past the threads, it will seep past the teflon too.

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Your 100% correct. It is used as a lubricant for threads. I wrapped the threads and we will see what happens. Most likely I will have to get a thicker o-ring if it starts leaking again. Just don’t understand why it is like this and nobody else is leaking seeing they use the same setup. I don’t get back to side x side to October, so I’ll see if it leaked just sitting there. My fingers are crossed.

thanks for your reply

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Its very possible there was a slight imperfection causing the issue too.

Orings are very sensitive to leaking if nicked or if it just doesnt sit right. Or could be a slight imperfection in the old bolt that caused it to sit just a little off.

Fingers crossed and let us know how it looks in october.

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