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Hylomar and sealant choices

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TomMull

TomMull

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I'm working on a ZF10M Marine transmission. The case is in 2 halves machined to high (supposedly) tolerance and gasket less. From what I gather, the recommendation is to use Hylomar sealant on the surfaces. My usual source, NAPA, doesn't carry it in stock. Would Permatex be a good substitute? If so, which one? My usual is Permatex Aviation but I know that's old school. After a quick Google search, I am overwhelmed by advertising hype and "branding" of sealants but find little of substance.
One thing to consider is to minimize the film thickness. I do not see evidence of sealant on the original assembly, so I assume that filling the gap with goo would not be a good thing.
Tom
 
Hylomar is good stuff and can be spread very thinly. If you can't find it locally, Amazon is your friend. And you can often receive orders in as soon as a couple days.
 
A sometimes available substitute for Hylomar is Permatex Permashield. It is of similar chemistry and performance to Hylomar Blue. Sometimes you will find it at places like Advance Auto. I have typically ordered it from Amazon.
 
I use this on my farm equipment, tractors etc. I've used it mating fuel tank sending units with no leaks. Has worked perfect for me for years, of coarse everyone has their favorite, I use what has worked for me and this is it. PJ
View attachment 51246
 
I have used both - one question I have (especially regarding things like the ultra copper and the like) is this.

I have typically used Permatex to llay a fairly thick bead - using it more like glue I suppose to either actually make a "gasket" or to adhere one. OTOH hylomar wants to be used as a very thin coating (as apparantly does the shellac)

Paul - do you use the ultra copper as a very thin coat and if so, how do you spread it? (Likewise other permatex products, thick or thin?)
 
In advance of Paul's reply I offer the following comments.

RTV in general should not be used on any fuel related systems. Regardless of what success others may have, RTV is attacked by gasoline. It will swell, ooze out of the joint, and cause problems elsewhere... like plugging fuel filters when it breaks off.

The Permatex Permashield product is like Hylomar. It is applied in thin coats and is made to be compatible with fuel.

I restrict my use of RTV to applications like valve cover gaskets where I use it to both bond and fill the irregular surfaces. I place the gasket on a very flat surface (like a sheet of MDF), apply RTV to the valve cover, then rest it on the flat gasket. When the RTV cures it both bonds the gasket to the cover and fills the voids where the valve cover is distorted.

EDIT: See the link below from the Permatex website about using RTV on fuel systems.
https://www.permatex.com/faqwd/can-use-permatex-ultra-blue-rtv-seal-gas-gauge-sending-unit-gas-tank/
 
JPSmit said:
I have used both - one question I have (especially regarding things like the ultra copper and the like) is this.

I have typically used Permatex to llay a fairly thick bead - using it more like glue I suppose to either actually make a "gasket" or to adhere one. OTOH hylomar wants to be used as a very thin coating (as apparantly does the shellac)

Paul - do you use the ultra copper as a very thin coat and if so, how do you spread it? (Likewise other permatex products, thick or thin?)
Click to expand...

JP, I spread it very thin with my finger and wearing mechanics throw away gloves. Saying that, I let it set for about 10 to 15 minutes before putting the part on. PJ
 
thanks for these replies - very very helpful!
 
Taking the unusual approach of reading the service manual for the transmission, I find the manufacturer's command that you must apply Loctite #574 to the mating surfaces and no mention of Hylomar although I know it is used extensively. No other options considered either.
Since the thing has never leaked even a drop in the past ten years, I decided to follow the command.
Of course, that stuff is not available locally so I ordered it from Staples for pick up in store. Unlikely source it would seem and not cheap but the best deal I could find.
Here's some product info:
https://na.henkel-adhesives.com/product-search-1554.htm?nodeid=8797713760257
Thanks all for the informative replies.
Tom
 
I like to use Permatex high tack gasket sealent. I use it on bare surfaces and it's fine.
 
number6 said:
I like to use Permatex high tack gasket sealent. I use it on bare surfaces and it's fine.
Click to expand...

Hey Tom, good to hear from you. I know I'm overthinking this, but my mind is back in the time when I had a can of Permatex Aaviation in my toolbox and that was it. Now I have a drawer full of various cans, sprays, and tubes of different goos and never seem to have the right stuff.
Tom
 
I've had good results with using Loctite 574 on many cast metal housings. Specifically with Porsche 911 and 930 engine cases. The Porsche sealant is even more pricey and the Loctite works just as well.

As for using any RTV compound for sealing any joint in contact with fuel, strictly a no-no for me. As Doug says, it softens the RTV and makes it "slime". I won't chance it getting into some small orifice and dealing with all the heartburn that would cause. RTV has its place, just not around fuels or other high evaporatives (xylol, acetone, lacquer thinner etc.).
 
DrEntropy said:
As for using any RTV...
I won't chance it getting into some small orifice and dealing with all the heartburn that would cause.
Click to expand...

There are so many bad places to take that.

Regardless, my first bad experience with RTV is when a very young and naive Doug used it (unnecessarily) on a BMW 2002's Solex carb lid gasket. I drove the car fine for a day... then it just died on me. Fortunately it did not take me long to find the strand of RTV goo in the carb's main jet.
 
My most recent bad experience with RTV was when a professional shop used it for the water pump gaskets on my Buick wagon. A few months later, a friend and I drove to Grand Teton national park so he could take photos of the sun coming up over the mountains. There is just a moment where the valley is still in darkness, but the sun peeps over the mountains on one side and lights up the snow on the tops on the other side. Truly a spectacular view!

But, it was about 5F when we got there (over an hour before dawn of course), and the heater just didn't work at all! The heated seats were the only saving grace and we were still both shivering from the cold. To add injury to insult, his camera didn't work right due to the cold.

Turns out that model has a restriction in the line to the heater, which according to the book limits the pressure inside the core at high rpm. The restriction was clogged with, you guessed it, RTV from the water pump.

FYI, this is the view he was trying to capture.
Grand%20TetonNPRobertBumanSTE%201200.jpg
 
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