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Mouse Milk?

DanH

Legacy Member
Mentor
Within the Continental/Lycoming community, Mouse Milk is often prescribed as a standard maintenance item for exhaust system joints. In the Rotax world, an anti-seize compound appears to be more popular.

What exactly is Mouse Milk? How does it prevent seizure of the joint?

I'll stir the pot...I don't see where it does much of anything. The ball joints on my AWI 4-into-1 eventually lock no matter how often the get they Mouse Milk treatment.
 

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Does it soften the various solid buildups in the joint, allowing it to grind away in the first seconds of the next engine start? Dunno.
 
Seen some of the Reno teams use it on wastegate valve stems to keep them smooth. Not sure how well it worked or if it just made you feel better.
 
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In the certified word Mouse Milk is pretty common. Not so much in EXP. I started using it on my Turbo Arrow 25 years ago, on all the exhaust joints. Never had a seized joint or bolt... I have a bottle of it right here in the hangar.
 
Seriously, I'm not seeing anything in there that would survive sitting on a hot exhaust.

https://www.mousemilk.com/Mousemilk_Penetrating_Oil_(USA)_EN_sds.pdf

Perhaps when you want to remove the exhaust and you need it to move a bit, putting some penetrating oil on there will help.

And there is this sales sheet:

https://www.mousemilk.com/MM_Tech_Spec_rev1.pdf

Ingredient list and sales literature says it's a penetrating liquid, like a great many other similar products, and possibly useful in loosening a stuck exhaust joint. Per the above sheet, it would work best if the joint was warm, but below the smoke temperature of the product. There's nothing to prevent seizure. The ingredients evaporate or turn to carbon at red hot temps.
 
Why bother?

I have my exhaust pipes supported by clamps that attach to the engine case, NOT to the engine mount. The engine and exhaust can move as a single unit.

I have the standard Veterman cross-over two-pipe system.

I have never put anything on the slip joints. Go ahead and let them seize.
I have removed them once (at about 500 hrs to install the new SDS induction pipe seals) and it was easy to drop the exhaust pipes off the engine. And they went right back on, in the same position they came off.

Given how much Lycomings shake, it seems like a bad idea to clamp the exhaust pipes to the engine mount. The slip joints seem like a bandaid to reduce loads into the exhaust when it is mounted in a way that puts loads into it. Better just to not put any loads into it at all.
 
I have my exhaust pipes supported by clamps that attach to the engine case, NOT to the engine mount. The engine and exhaust can move as a single unit.

I have the standard Veterman cross-over two-pipe system.

I have never put anything on the slip joints. Go ahead and let them seize.
I have removed them once (at about 500 hrs to install the new SDS induction pipe seals) and it was easy to drop the exhaust pipes off the engine. And they went right back on, in the same position they came off.

Given how much Lycomings shake, it seems like a bad idea to clamp the exhaust pipes to the engine mount. The slip joints seem like a bandaid to reduce loads into the exhaust when it is mounted in a way that puts loads into it. Better just to not put any loads into it at all.

I agree that I prefer to mount everything to the engine, and let it all shake, rattle, and roll together. The only thing that you might be forgetting is that the cylinder heads move considerably relative to one another ( you should see a slo-mo of a Lycoming running sometime), and my experience is that when these exhaust systems get some age into their metallurgy, they become brittle. When a pipe lets go, I frequently don’t see cracks so much as full circumferential breaks, and all at once.

So the slip joints are there to help the pipes move with the cylinders, not just relative to the airframe. As to mouse Milk? I use it, but only because I have a bottle, and Vetterman told me to.... I make no claims for or against it!
 
I use MM on my AWI collector slip joint, and make a loose mix with a nickel antiseize to wet the ball joints more easily. I usually remove the collector and move each pipe (exercise the ball joint) around until the mix gets in the ball joint.

I have to use it for something. I might think the wetting of the slip joints allow the seized spots get a little lubricant, then wiggle loose on first start and return to a dry joint.
 
I agree that I prefer to mount everything to the engine, and let it all shake, rattle, and roll together. The only thing that you might be forgetting is that the cylinder heads move considerably relative to one another ( you should see a slo-mo of a Lycoming running sometime), and my experience is that when these exhaust systems get some age into their metallurgy, they become brittle. When a pipe lets go, I frequently don’t see cracks so much as full circumferential breaks, and all at once.

So the slip joints are there to help the pipes move with the cylinders, not just relative to the airframe. As to mouse Milk? I use it, but only because I have a bottle, and Vetterman told me to.... I make no claims for or against it!

Seems like a good enough reason for me!
 
I have my exhaust pipes supported by clamps that attach to the engine case, NOT to the engine mount. The engine and exhaust can move as a single unit.

I have the standard Veterman cross-over two-pipe system.

I have never put anything on the slip joints. Go ahead and let them seize.
I have removed them once (at about 500 hrs to install the new SDS induction pipe seals) and it was easy to drop the exhaust pipes off the engine. And they went right back on, in the same position they came off.

Given how much Lycomings shake, it seems like a bad idea to clamp the exhaust pipes to the engine mount. The slip joints seem like a bandaid to reduce loads into the exhaust when it is mounted in a way that puts loads into it. Better just to not put any loads into it at all.


The lengthening of the pipes due to thermal expansion is considerable, and they warm up a whole lot faster and a whole lot more than the cylinder heads/crankcase assembly. I can see the scuff marks/witness marks of about .200" on the telescoping joints of the crossover pipes.

The thermal expansion coefficient for SS is somewhere around (6E-6)in/in/*F. If the pipes get to an average of 1200 degrees in this segment, and assuming it is about 24" long from side to side, it generates a length change of about .160". My guess of the observation to be .200" might not be far off. The crossover slip joints, if not allowed to telescope, would cause badness to happen very fast.
 
Like many other Vetterman customers here, I began using Mouse Milk over twenty years ago because Larry recommended (insisted) I use it. Until a few years ago I had no real data point that Mouse Milk was any different or better than any other penetrat or anti-seize. I now know, at least in part, why Larry recommends Mouse Milk.

Owners of aircraft with a Rotax power plant are well aware that broken exhaust springs are a regular occurrence when using the high carbon steel (Rotax supplied) springs. Subjected to high exhaust temperatures, the springs also become covered with a light brown heavy rust almost immediately after first use. Humm... if Mouse Milk is the cat's meow for Vetterman's exhaust, it surely must be good for a Rotax. Applied Mouse Milk to the springs and ball joints. The springs immediately took on a nice dark wet color. Well, I thought, we'll see how long that lasts.

Been using Mouse Milk on the Rotax exhaust springs for over seven years now; springs retain the dark wet look between oil changes (no more rust) and spring breakage events reduced 80% or better. For those that are surely going to ask, yes, I've used the stainless springs supplied by ACS but they don't provide the same tension as the steel springs. There ya have it... repeatable results demonstrating the magic contained in a bottle of Mouse Milk.
 
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I agree that I prefer to mount everything to the engine, and let it all shake, rattle, and roll together. The only thing that you might be forgetting is that the cylinder heads move considerably relative to one another ( you should see a slo-mo of a Lycoming running sometime), and my experience is that when these exhaust systems get some age into their metallurgy, they become brittle. When a pipe lets go, I frequently don’t see cracks so much as full circumferential breaks, and all at once.

So the slip joints are there to help the pipes move with the cylinders, not just relative to the airframe. As to mouse Milk? I use it, but only because I have a bottle, and Vetterman told me to.... I make no claims for or against it!

Yes, adjacent cylinders move quite a lot. A surprising amount.
But two adjacent cylinders are on separate exhausts. So no load occurs from that.

There may also be some relative motion between the diagonally opposing cylinders that are on the same exhaust. But since the piston motions are out of phase, the cylinder motions may also be, so the relative motion across a diagonally opposite pair may be fairly small? There is quite a lot of length of pipe between them too. So, I don't know - maybe my slip joints move more than I think. Either that, or there is just some flexing in the higher temperature, lower modulus portions of the pipes.

Anyway, 600+ hrs with no apparent issues (yet).
 
The lengthening of the pipes due to thermal expansion is considerable, and they warm up a whole lot faster and a whole lot more than the cylinder heads/crankcase assembly. I can see the scuff marks/witness marks of about .200" on the telescoping joints of the crossover pipes.

The thermal expansion coefficient for SS is somewhere around (6E-6)in/in/*F. If the pipes get to an average of 1200 degrees in this segment, and assuming it is about 24" long from side to side, it generates a length change of about .160". My guess of the observation to be .200" might not be far off. The crossover slip joints, if not allowed to telescope, would cause badness to happen very fast.

I think there are some flaws in your assumptions. Certainly the first several inches of pipe sees a 1200+ delta T. Those sections of pipe are vertical and parallel between the two pipes on an example. So they just elongate together. The portions of pipe where the bends are, and then more horizontal run toward each other, are lower delta-T. Still significant, no doubt, and must produce some bending stress at the flanges where the pipes attach to the cylinders. I don't see how the spherical joints do anything to relieve that load anyway. My Veterman system does not have any longitudinal slip joints - those joints have lugs that are bolted together across the joint. they don't move.

I'll definitely update these posts if I ever do have a failure.
 
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I think there are some flaws in your assumptions. Certainly the first several inches of pipe sees a 1200+ delta T. Those sections of pipe are vertical and parallel between the two pipes on an example. So they just elongate together. The portions of pipe where the bends are, and then more horizontal run toward each other, are lower delta-T. Still significant, no doubt, and must produce some bending stress at the flanges where the pipes attach to the cylinders. I don't see how the spherical joints do anything to relieve that load anyway. My Veterman system does not have any longitudinal slip joints - those joints have lugs that are bolted together across the joint. they don't move.

I'll definitely update these posts if I ever do have a failure.

Steve, I didn't know some crossovers didn't have telescoping joints. Here's a crummy picture I dredged up of the front crossover on mine:

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One can see that the relative motion is about half the hex dimension on the hose clamp. Those are 5/16" IIRC, so the motion appears to be in the neighborhood of .150". If I remember, I'll put a caliper on that the next time the cowl is off. The other crossover has the same witness scuff marks as the one in the photo.
 

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One can see that the relative motion is about half the hex dimension on the hose clamp. Those are 5/16" IIRC, so the motion appears to be in the neighborhood of .150". If I remember, I'll put a caliper on that the next time the cowl is off. The other crossover has the same witness scuff marks as the one in the photo.

Alex, that relative motion could easily be the result of start-up shake.

I use MM on my AWI collector slip joint, and make a loose mix with a nickel antiseize to wet the ball joints more easily. I usually remove the collector and move each pipe (exercise the ball joint) around until the mix gets in the ball joint.

Nickel anti-seize makes a lot of sense.
 
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The slip joints on my turbo Subaru exhaust show similar movement to what Alex posted- around .150 in my case. Yup pipes move within slip joints. That's why you should have them if there is differential movement. Tremendously reduces mechanical stress and the chance of cracks. I've seen lots of exhaust systems crack over the last 40 years because they didn't have slip joints- some in only a handful of hours.
 
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Dan - from left to right side of the engine? I can't imagine that.

Maybe not. Easy to check. When cold, stick a strip of aluminum tape across the joint, crank it, and shut it down right away. If it's shake, it will tear the tape.

Returning to Mouse Milk, does anyone have reason to believe it has any property other than being a solvent? Or that it offers any lubricant or anti-seize effect after the first time the pipe reaches operating temperature?
 
mouse milk. it's got to be good because mice use it all the time. mix it with some Marvel Mystery Oil and you have mystery mouse milk, even better.

I apply it every chance I get. Never a problem.

850 hrs on exhaust system and I haven't touched anything since new.
 
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Seems like this subject kind of faded away. Had Vetterman repair my 20yo exhaust last year and I'm adding Mouse Milk wondering if this is doing anything. The anti seize does seem like a good idea. Any new info?
 
The first time I heard of using this Mouse Milk on the exhaust, I couldn't have laughed more.
I told the guy he was crazy as a Loon. He says he was taught that way.
Ain't no way it is going to help anything at exhaust temperatures.
Slip joints= good Ball joints= good.
Mouse milk is pure and simple a joke and of no help for life cycle as far as I can see
If your disassembling something it will help free it up, But, there are far better lubes for that.
We use it in milling machines and drilling, But, not on exhaust systems to keep them free. Cause it's cheap and works there.
Exhaust systems move a lot during the high heat cycles on there own and need joints in air cooled engines like we run.
I just laugh every time somebody thinks they need it and tell them to just look at the proof.
Now Nickel seems to help quite a bit.

My three cents worth Art
 
What technique are folks using to apply the Mouse Milk? The angle of the exhaust joints make applying the Mouse Milk with the supplied bottle difficult.

Turkey baster?
Syringe?
 
What technique are folks using to apply the Mouse Milk? The angle of the exhaust joints make applying the Mouse Milk with the supplied bottle difficult.

Turkey baster?
Syringe?

You can stick a straw in the tip, but I like to just put some in one of those need-tip squeeze bottles. That said, I don't think it does much. If anything, maybe dissolves some carbon...maybe.
 
What technique are folks using to apply the Mouse Milk? The angle of the exhaust joints make applying the Mouse Milk with the supplied bottle difficult.

Turkey baster?
Syringe?

Just dip a small flat screwdriver in the container (allow it to stop dripping) and touch to top of joint. Do this several times and you will see it suck right into the joint.

Does it help the joint?? It is cheap and easy to apply. I apply it every time cowl is off and have never had ANY problem with my exhaust.

It is not designed to lubricate a hot exhaust joint. It is designed to dissolve carbon buildup in a cold joint, to keep it form building up and locking the joint. A clean joint will expand at the same rate. When carbon builds up in the joint, it does two things.... it reduces the designed space needed to move, and it insulates the the two parts so the inner part expands more than the outer part and with the space filled with carbon, it locks up.

By design, the stainless joint would not seize if only clean hot air was passed through the joint. But when you add all of the by products of combustion and some lead, it will leak into the joint and over time, clog (seize) it up if not removed. Look at the buildup on your exhaust valve, exhaust port and even the tip of of the exhaust pipe.
 
MM Application

I use a syringe from Tractor Supply with a curved metal tip.
I use it cuz Vetterman said to.
It’s too cheap not to and Nearing a 1000 hours and trouble free exhaust. I use MMO in my gas for the same reason.
 
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