Richard Seccombe

Hi Everyone,

This is my first post on this forum. I have a 40’ Trojan with two 496 Horizons (not HO’s). Based on all of the posts regarding the use of the Rinda Diacom software and the Mercruiser PCM 555 manual, I purchased both and spent hours on both engines monitoring every parameter. I have to say, I learned an amazing amount beforehand by beating up this forum reading everything I could find that had either Rinda or Diacom in the text.

All of the engine parameters seem to be well within spec and the only trouble codes (both active and Freezeframe) I could find were the standard ones that get thrown because the sensors aren’t installed.

My main question is regarding the Sea Pump Pressure. A week ago I had the impellers replaced just as a standard maintenance procedure. The old impellers were intact but a bit hardened and there were some fine small circular scratches in the housing. I went ahead and replaced the impellers but not the entire pumps. When I first fired up the Diacom software the pump pressure was reading between 5 - 18 psi. I couldn’t find anything in the PCM 555 manual that quoted what normal is. I shut the engines down and cleaned both raw water strainers. There was very little in the strainers but when I fired the engines back up, I then got between 25 – 40 psi and the pressure isn’t necessarily related to the engine RPM (idle to 2000).

I suppose there could have been something in the water lines that broke free by just pulling the strainers in and out but would like to know what is the normal pressure and if small scratches in the housings can make a big difference in performance. At about $500 per pump I’m hoping to go with what I have for a while. The manifold exhaust temps are between 110 – 120 F. and the engine temps stay between 154 – 159 F.

Any incite or suggestions would be very much appreciated.

Thanks,
Richard

Wally

iTrader: (1)

"normal" will depend on where the sensors are reading the water psi...i have been told that most engine dont like to see more then 20psi inside the engine blocks due to head gaskets failing beyond that point...true/false i dont know. Most boats i have been on that had the psi gauges never read more then 15psi.
I work for a company that makes transfer pumps....we actually did a test on the merc pump just to see if there was anything we could incorporate into a new pump design of our own....the merc pumps can easily generate 45+psi when restricted enough....
So if you got a jump in psi it could very well be bacause something got loose and is causing a restrcition....could be as simple as a piece of rust flaking off and partially blocking a water passage.

BenPerfected

I agree with Wally in that it is mostly about the flow not the pressure. We keep our water pressure with 2-stage KE sea pumps between 12-14 LBS because we have plumbed for exits in two places in the tail pipes and also off the intake manifold. We run little water temp but 218 oil temp.
I am also betting that somewhere you have a restriction that is pushing up your water pressure.

Boat Tech

Are you reading this while on the trailer or while on the lake? If on the trailer then you might be pushing to much water thru the system and giving the sensor a bad reading. You say you have too engines are both engines showing the same psi now or just one? Do you have bravo 1s? and if so are you covering up the low water pick up holes if you are no the trailer with the garden hose hooked up? You might just have a sensor that is just out of range or damaged while doing the new impellers, [just a thought their] also just another thought don't take this the wrong way but I believe the scan tool has too styles of reading info to give out one is standerd and one is metric are you on the right setting. And you are right the normal specks that I am use to seeing is any where from as low as 0.3psi on the trailer up to around 6.0 while reving up on the hose and as hi as 17.5psi on the lake at WOT on stock set up's.

Richard Seccombe

Thanks everyone for your input. The boat is in the water in a slip when I'm doing the testing. It seems strange that both engines ramped up on pressure by just removing and replacing the strainers. One strainer had just a little junk at the bottom of it and the other had nothing.

I checked to see if the Diacom software switched over to Metric and it had not. All of these tests were done with the boat sitting in the slip and in neutral. I plan to take it out and really put the wood to it later this week to see what kind of readings I get.

I'm a little confused on the readings...if there is high pressure, does that mean that there are restrictions in the flow and the pump is working hard to get anything circulating? In other words, if you had a bad impeller and very little water was flowing through the pump, would that show high pressure or low pressure? I am suspecting that a bad impeller would show very little pressure.

Thanks,
Richard