Is this an SX-M drive, and is it worthwhile to have a water pressure gauge on an I/O?

[kmdigital]

Here's the info for my engine and outdrive, M# 302CPBYC, S# T1307301, drive is M# 3868814, S# T0818545, which I think is the Penta SX-M.

Is there anything special I should know or be on the lookout for regarding this combination? It's interesting that I can't find this outdrive model number in any of the Penta links or literature when looking up replacement parts, which is where the confusion comes from.

After having someone that was borrowing another boat smoke the outboard some years ago, I've always installed water pressure gauges on my outboards since then so that it was easy to verify cooling water flow. I don't know if this would be helpful on an I/O, or if it's even possible to read any water pressure if a gauge is connected to the block, such as on the bottom of the exhaust manifold. I'm not sure which side of the block the thermostat is located, but assume most likely outlet. However, I don't know if there's enough water pressure from the raw water pump inside the block to be read reliably on a 0-30 PSI gauge.

There's no place on the dash for a gauge, but I could mount it underneath or on the side where it's easily visible from the driver's seat, if it's feasible and useful. It already has a temperature gauge, so maybe this is overkill, I don't know.
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thanks

 

[bruceb58]

I think the problem is that you can have good pressure but low flow with a worn impeller. That along with a plugged up manifold, the pressure will look fine.

I am sure many have done it. Just not sure it buys you more than looking at the temp gauge.

 

[kmdigital]

I think the problem is that you can have good pressure but low flow with a worn impeller. That along with a plugged up manifold, the pressure will look fine.

I am sure many have done it. Just not sure it buys you more than looking at the temp gauge.

Hmm, that seems a bit odd "good pressure but low flow with a worn impeller". It would seem to me that pressure is directly related to flow, but I guess it depends on how the water makes it out of the block. Is there some sort of check valve or spring relief that opens when the pressure reaches a certain level? If it's just open out through the exhaust with nothing to impeded the flow, then flow and pressure should be directly correlated. It takes more flow to create more pressure and vice versa.

However, if there's something that requires specific water pressure to be reached before it exits the block, then I can see that there wouldn't be that much correlation between flow and pressure. Just wondering.

 

[bruceb58]

It takes more flow to create more pressure and vice versa.

Measure the pressure of the water system in your house with nothing turned on and you can see how you can have pressure with zero flow.

There is no check valve. The system is wide open.

 

[kmdigital]

Measure the pressure of the water system in your house with nothing turned on and you can see how you can have pressure with zero flow.

There is no check valve. The system is wide open.

As a plumber, that's not a correct analogy. The pressure is highest when nothing's turned on, as there's no flow. For example, turn on all the faucets in the house and then check the pressure. It may be almost nothing, depending on the initial pressure, the source water supply pipe size and the size of the piping in your house. The pressure will be the highest with no flow and will drop the higher the flow.

Anyway, just as a check, I installed a pressure gauge in the exhaust manifold, and even at WOT, it's only about 2-3 PSI, so not worth the effort and doesn't tell you much of anything. This is actually what I expected if there isn't anything that prevents the water from existing the engine essentially as fast as the raw water pump supplies it. The temperature gauge works well, so will just have to rely in it to monitor proper cooling water flow.

 

[bruceb58]

As a plumber, that's not a correct analogy. The pressure is highest when nothing's turned on, as there's no flow. For example, turn on all the faucets in the house and then check the pressure. It may be almost nothing, depending on the initial pressure, the source water supply pipe size and the size of the piping in your house. The pressure will be the highest with no flow and will drop the higher the flow.

Yep, you said it better but that is what I was trying to say as well.