Dissimilar Metals question.

[Newf]

I just installed an oil pressure sending unit and gauge on my D1-30 Volvo Penta. It only had an alarm originally. To facilitate installation of the sending unit I had to use a 90 degree fitting. I used brass and this is screwed into aluminum casting. I've later read that brass and aluminum is a no-no but also read that stainless fittings screwed into aluminum is not much better. I also read that it would be OK and to just paint the fitting and attachment point with a high zinc paint.

What should I have done to reduce any issues associated with dissimilar metal corrosion? The oil port that I used had a carbon steel allen head plug in it originally. Any thoughts on a better solution would be appreciated.

 

[Buckethead905]

If the dissimilar metals are placed in an electrolyte solution (salt water) then you will create a charge, thus creating a battery, which would lead to galvanic corrosion. If it’s an oil pressure sending unit there would be no electrolyte to facilitate the electrolysis. You will be perfectly fine. Many automotive fittings are of dissimilar metals. Maybe @noluck has some more insight into electrolysis within automotive fittings. I can’t see engine oil being a electrolytic solution. Also brass is not very corrosion resistant, bronze is a much better solution. Brass is rather low on the periodic table (given the components it’s made of as brass is not an element itself)

 

[Prfisher]

Even just in a marine environment, brass & aluminum will react. In my experience good quality stainless doesn’t pose a problem. Cheap offshore stainless... no guarantees.

 

[Wild Bill]

STainless that Greggs sells is pretty good looking stuff. DIesel and higher vibration stuff I have had brass snap off when you touch it.

 

[Newf]

Thanks for the replies. Just to be on the safe side, think I'll swap it out for stainless. Not something you want to fail. This engine shakes like a bugger at idle when trolling so it is probably the right thing to do. It's 1/8 NPT and Trotac, which is where I bought the sender and gauge, just had the brass fitting. I'll check out Greggs.

 

[gungadin]

You are going to have to keep close watch on that. If there is as much vibration as you say, there is a fair chance that over time the fitting will crack and break off. That's quite a bit if weight hanging out there. If I may, I would like to suggest that you make a mount utilizing those two brackets to the left of the sending unit. Run a straight piece of pipe up to the mount

 

[Newf]

You are going to have to keep close watch on that. If there is as much vibration as you say, there is a fair chance that over time the fitting will crack and break off. That's quite a bit if weight hanging out there. If I may, I would like to suggest that you make a mount utilizing those two brackets to the left of the sending unit. Run a straight piece of pipe up to the mount

Thanks for your suggestion. I agree, this does look problematic but is what I've seen done on another engine like this and was where I got the idea.

To clarify, what are you referring too as the two brackets? There is a lifting lug to the left and two locations, one with an existing bolt, in the valve cover. Cover is also aluminum. Also you suggest running a straight pipe up, so are you thinking I could then mount the sending unit vertical or still go with the elbow? I didn't clarify in my post but I can't mount it vertical because there's not enough clearance to the underside of doghouse.


Appreciate your input.

 

[gungadin]

The way you have it set up now will cause the sending unit to vibrate considerably. Because it is long and heavy it acts as a lever on the 90 degree fitting. The weakest point of that fitting is where it screws into the oil gallery. That is where it would break. It will leave a short piece of threaded material in the oil gallery that would require an easy out to remove. It would likely be unnoticed for a while, and could cause some damage to the engine internals due to lack of lubrication, to say nothing of the mess and fire hazard. The weakest point of the mechanical connection is always going to be where it screws into the oil gallery. As mounting it vertical would interfere with the doghouse, you might want to consider mounting a bracket in another location on the engine close to the oil gallery and connecting the oil gallery to the sending unit with a piece of flexible stainless (or other material) hose with the appropriate fittings. Most hydraulic shops have the tooling and fittings to make up a hose for you, remember to include a couple of loops in the hose to help absorb vibration, if you go this route.

 

[Prfisher]

The way you have it set up now will cause the sending unit to vibrate considerably. Because it is long and heavy it acts as a lever on the 90 degree fitting. The weakest point of that fitting is where it screws into the oil gallery. That is where it would break. It will leave a short piece of threaded material in the oil gallery that would require an easy out to remove. It would likely be unnoticed for a while, and could cause some damage to the engine internals due to lack of lubrication, to say nothing of the mess and fire hazard. The weakest point of the mechanical connection is always going to be where it screws into the oil gallery. As mounting it vertical would interfere with the doghouse, you might want to consider mounting a bracket in another location on the engine close to the oil gallery and connecting the oil gallery to the sending unit with a piece of flexible stainless (or other material) hose with the appropriate fittings. Most hydraulic shops have the tooling and fittings to make up a hose for you, remember to include a couple of loops in the hose to help absorb vibration, if you go this route.

I did exactly as you said on my sailboat after pumping four litres of oil into the bilge. Those treaded fittings do have a weak spot in the male treaded portion. Bitter experience... I used rubber oil pressure hose to the sender, which I mounted on a nearby bulkhead. You will have to run a ground wire to the sender if it was getting its ground through the mechanical connections before.

 

[Newf]

Thanks for your thoughts. I will look for a solution to support it as is, with a stainless fitting instead of the brass one, or I will mount it somewhere using a flex hose. Always good to get other opinions,,,,,that is why I love this forum so much. So much knowledge and willingness to share. Thanks again.

 

[Prfisher]

P.S. Newf... like yours, my sender didn’t have a ground lug. I sanded off a small spot of the cad plating & soldered on a blade connector. Ran the wire to a common ground point on the block. (Just in case you decide to go that route. )