Warm water in bilge
 

1997 502mpi motors. I have warm water in the bilge and cannot figure out where it is coming from. The port motor pressure gauge hold steady at over 35mph but the starboard Guage will bounce between 30 and 15lbs. If the water was cold then I would say I have a leak but again it is warm so I believe it is from the one motor but I can't locate it. So I have 2 questions does anybody have any suggestions and can I pressurize the motor when the boat is on the trailer?
I have run the motors on the hose in the driveway but can't seem to find any thing and when on the water at lower speed or idle I see no water coming from anything. Any help would be appreciated.

Any chance one of the drain petcocks is leaking?

dont know where you are located but did the blocks get winterized properly ? being warm its aft of the sea pump, there should be block drains both sides just above the pan rail, oil & ps coolers should have drains also

I would say the winterizing is fine because the motors run strong and I have no other issues. Also the water really seems to accumulate faster at higher speeds. Also the water pressure gauge bounces only at higher ram. Almost like there is a pressure relief somewhere.At idle or low rpms it seems like no water is coming in to the bilge.
Do you have any thoughts on how to pressurize the system? I was thinking about hooking up a low pressure pump to the engine flush to see if that would show the leak.

Leaking circulation pump? Lose hose clamp?

I just put 2 new sea pumps on to eliminate that problem and I don't see any water coming out of the circulating pump but I will check again along with the block drains.
You would agree the motor with the fluctuating water pressure is probably the problem?

you may have some blockage in the system did you back flush before putting the new sea pumps on, I think 30psi is a bit much for those motors

Get creative with cell phone vid or GoPro type camera. Mount near warm water sources. Ie: block drains, recirc pump/ exh hoses and drains

No I did not. The impellers in the old one were still in tact. I thought maybe one of the housings was cracked and rather then rebuilding them I chose to install 2 new ones.
Would it be possible the oil cooler has a crack in it that only opens up under higher pressure?

I agree on the go pro idea. Just need about 3 of them I think.
Any thoughts on how to pressurize the system when boat is on trailer

Check you exhaust hoses and clamps. Sometime they will leak at higher pressure/RPM's. Seen it more than one. Had the same symptoms on my own boat, chased that water in the bilge issue. Took a mirror and went around all the exhaust hoses and clamps. One was not even all the way around. loosened it up and moved it even, water leak gone. Rechecked a couple of weeks later and it was about 1 turn loose. .

My 2000 502mpis have high water pressure too. Higher than I like, but its been that way since I bought it 600ish hrs ago. With new impellers, they will peg the gauge at 35+ at WOT.

Ok will check all clamps again. You do agree the leak is from the starboard motor because of the fluctuating water pressure?

Also isn't the water in the exhaust no longer under pressure? Because the gauge is moving up and down I keep looking after the sea water pump but before the exhaust. Am I correct on this?

Bilge doubles as a hot tub , I don`t see what the issue is.

Not quite the answer I was looking for but funny anyways.

Crack in the block? I'd look for rust on the block also.

I need to get back in there and look again. When I changed the exhaust I did not see anything unusual. Also when I run it on the hose I get no water in the bilge but of course I can get the same extended amount of water pressure.

look at the freeze plugs while you're upside down

Crud in the water end of the oil cooler causing the pressure to rise and push water past a hose clamp?

I would lay some sheets of cardboard on the bilge floor and do a very brief run to get the water pressure up. The cardboard will make it easy to see where the water is coming from.

That's a good idea.

Try thread sealant on block drains, check the intake gasket at the rear, check the weep hole on the circulation pumps. Buy a bore scope camera from Harbor Freight to inspect areas you can't see easily.

Camera ordered will be in tomorrow. I will check all of the areas you and the other posts mentioned. Last but not least will be the cardboard run.

I just put EMI manifolds on mine, had a small leak when fired up on hose. Hose clamp wasn't loose either. The hose clamp had sliced the hose, when I wiggled hose leak increased. Trimmed an inch off and re-clamped. Issue solved.

Id go through an wiggle/check every hose connection. Likely a similar issue, especially if warm water.

If you have sea strainer try putting RED food color inside the sea strainer.
That will show you where it it ........

Being not familiar with that engine I just was going by what a 454 has, which is a drain petcock on each side of the block plus one for each side of the exhaust, sometimes an oil cooler or power steering cooler, Cool Fuel, etc.

As others have mentioned, look at the block. High water pressure on a 502 can cause the head gaskets to leak to the of the block. My 502s also pegged the water pressure meter at higher rpm and speed.

Hoping it's just a hose leaking. Let us know what you find.

Do you mean to the back of the block?

Down the sides. The exhaust can hide it from view. They’d have to be really bad to drop noticeable warm water though.

Heat exchanger/oil cooler at the back of the engine maybe. I had to replace mine.

Run your motors with your boat on the trailer with drives down at a launch when it’s not busy… if that’s an option. This will allow you to bring your rpms up and not be dependent on the hose. Another if…put it in gear and put a load on the motor IF you’re not going to destroy the launch. Back in just far enough for your water pickups so your boat doesn’t end up in the back of your tow rig if you do put it in gear.