Bill272

HP500's and a milkshake

Boat is a 95 336 with Gen V HP500's. We took the boat out last weekend for the shakedown cruise, put on a total of maybe 45 minutes over 2 days. One engine just had a refresh, and when I checked the oil, we got milk. The engine builder came over yesterday and pulled one exhaust that seemed to be steaming more than the others (on the refreshed 500), and there's a leak around a stud at the top of the manifold. That stud had broken off at disassembly and was fixed with a helicoil. That explains the water in the one.

Now on the other, actually both, the idle was running very low. It was also dropping a lot when I put in gear. We did have to idle for a while both days and I looked down and saw the idle had dropped to around 500 rpm and even stalled a few times (especially when docking, going in and out of gear.)

I did some research and found Teague on Tech articles that address the HP500 reversion problem and Merc's service bulletin that these engines should not idle below 750 RPM in gear because of reversion issues with the Gil exhaust. Is the running at low idle and the idle dropping from 750-900 down to 250 before goosing it back to life a reasonable explanation for the water in the oil?

My thoughts are to do this: Fix the leak in the helicoil, get the idle set correctly, change the oil a few times and run it. My engine guy mentioned throwing 4 new manifolds on, but I'd like to try the fix first before throwing a couple grand at a problem that might not be there.

Does this sound like a reasonable path to take?

OK, I typed this out last week and didn’t post it. Yesterday I put a hose on the older engine to test the manifolds for leakage. There was some water up at the top of the manifold around the flange when I pulled the tailpipe that I would attribute to reversion. No leaks showed up when the system was pressurized, but when I pulled the inlet hose off the front of the t-stat housing, there was a slight oil sheen on the water.

Help, what’s my next step…

WILDTHING TAZ

If These Motors Never Did This Before Your Engine Builder Touched Them. Then I Think He Is Full Of Hot Air. I Run Gill Type On Wildthing With 540's At 600 Hp. All Day Long. I Had Trip 500 Hp In Before For 5 Years. I Say Head Gaskets!!!!or A Cracked Block Or Something Of That Nature. Water Can Only Get To Oil A Few Different Ways. Gill Type Exhaust Has Been Running For A Long Time. I Have Never Heard That They Are The Cause Of Water In The Oil.

Jonas

i had gill on my old 35 fountain and never an issue.. but i have heard that reversion issue many times over, i think it has to do alot with cam selection..
i would check intake maifold too as that is where i had an issue in another boat.

i think wildthing is onto something,,
its scary once oil been there as now u could be looking at other issues... yikes dont want to put a whammie on u,, but i would have the guy yank and check so u dont ventilate the block in 10 hours and he washes his hands with it.. due to time or whatever other excuse they cook up,,

i hate to hear that as season is here good luck hope it works out fast for you

T-N-T Sales

Do you have internal exhoust flappers? The 500 with Gil exhoust must have them. If you do, make sure they are not broken. The flappers disrupt the suck back pulse from cam overlap. I would recomend you start there.

Bill272

Well by the bare post running vertically in the center of the exhaust tip, I'd say that I had internal flappers at one point. A couple don't even have the post anymore. I do have the external Salisbury flappers and took the Silent Thunder platform off before the last run of last year. I wonder if the external flapper sealed better on the silent thunder box, acting more like the internal flappers than the big rubber external ones that kind of hang open due to the negative angle of the transom.

I talked to Rod Dash who rebuilt the one engine last year just before we bought it. He said that the reversion is definitely and issue with the idle that low and can get water in the oil. He mentioned that they pressure test with air so tonight I put 25-30# of pressure each manifold and they held it. There was no gurgleing or hissing or any sound at all from the tailpipes, so I believe that at least the 3 (couldn't test the one with the leaking helicoil) are fine. Another reason it could be reversion is the design of the tailpipes. They're tall and don't have much of a dropl, I assume because the engines sit low in the hull and the exhaust was designed to exit up near the platform for the exhaust box. Here's a pic:

WAGS382

Bill272
I have had reversion trouble on my 311 with 454's that were slightly more radical than the HP500 with the gill exhaust. They would milk the oil in a short time if the idle was low and the mufflers open. The end of the tail pipes were the old style with three holes to mix the water with the exhaust, a friend of mine who worked for gil marine suggested that I have the end of the pipes reworked to the new style so the water would go out the end of the pipe. The reworked pipes fixed the problem and I could even leave the mufflers open when at idle. I recently purchased a 1998 382 and had the pipes on it reworked before I launched it. Did your engine builder change the cam profile from the original HP500? Also mufflers will lessen the pulse going both ways helping to prevent reversion and defiantly keep that Idle up around 700-800 rpm in gear. Change the oil and take it out for a long run to chase the condensation out of the motor. Good luck. Jeff

Scott

"The end of the tail pipes were the old style with three holes to mix the water with the exhaust, a friend of mine who worked for gil marine suggested that I have the end of the pipes reworked to the new style so the water would go out the end of the pipe. The reworked pipes fixed the problem and I could even leave the mufflers open when at idle."

Can you give more specific details or pictures?

T-N-T Sales

Bill 272,
Get the internal flappers. At first I had a hard time believing that a disruption in the back pulse from the flapper would do anything, (I was told to do this by the people who make the Black engines) however after fixing several boats with this same problem I am convinced. Your Tailpipes stop inside the transom and connect to the tip with a rubber hose, so the water mixes with the exhaust closer to the engine (the water does not have to travel so far to get in the motor) As suggested, you could extend the tail pipes thru the transom and put the water outlet holes at the very end of the pipe. The draw back is the expense and major increase in noise. The external flappers will not do the trick. Try this before you beat up you engine builder, it probably has nothing to do with his work.

WAGS382

I was not talking about lengthening the pipes and putting the water holes outside the transom. The tail pipes I am talking about were wet gil offshore pipes with the rubber hose inside the transom connecting the pipe to the exhaust tips. If you look in the outlet end of the old style pipe the inner and outer pipe are swedged together all the way around with three hole in the inner pipe, causing the water to shoot to the center of the pipe. If you look in the end of a new style pipe you will see that the inner and outer pipe are not swedged all the way around, leaving gaps so the water shoot out the tail end of the pipe helping the reversion problem.

T-N-T Sales

Wags382,
Interesting, is there any flapper in your system? Did you new boat have 500's?