HARRISONMIRAGE

To answer your question I would change the bypass and your problem should be solved.I had the same problem plumbing a truck with a remote pad kit.The oil would not go to the cooler due to the bypass valve.The cooler wouldn't even get warm.I ended up using the block ports to get it to flow to the cooler.Extreme heat can also be caused by detonation and other nasty things but I think your problem is the 5$ valve that requires engine removal to install.You should have got a memo when you got this motor from GM.

Wobble

I have been dealing with this issue, Changed the bypass in the block, put everything back together then found same problem. Turns out that some MERC screw on adapters for oil coolers also have a bypass built in. If you have higher than stock oil pressure this thing opens and stays open. Had to take engine back out because Cast Oil pan didn't allow removal of adapter. Decided to plug all bypass valves, block and adapter, put small mech oil guages before and after filter to watch filter condition. This gave dramatic reduction in oil temps. I also have the 3x22 combo oil cooler with 580HP it is apparently not enough for extended hard running. Am looking for economical upgrade for this piece.

Mark

HARRISONMIRAGE

As Mark said that is a sure way to force oil through the cooler and filter by pluging the bypass.Just make sure you monitor pressure on both sides of the filter and use a high pressure filter.

Wobble

I beleive the Adapters with built in bypass were fitted to gen 4 motors. So this is something to watch out for if you install Gen5 or 6.

Mark

Kidnova

HARRISON, Great explanation. I was surprised at how many engine guys are not aware of this problem. A respected local guru offered this; usually marine mechs do a rebuild with an existing damaged marine BB like a 454 or 502. Or if they start from scratch to build a monster they'll buy a new Merlin or Bow Tie block, and go from there. So not many builders run in to the bypass valve situation. Makes sense, but it still sucks.

About the only thing I haven't done yet in relation to the oil temp dilemma is change the impeller in the sea pump. Never a problem with engine water temp, so I assume the impeller is still good, and is therefore pushing enough water through the oil cooler. But to be safe/sure, the impeller will get changed when the valve gets changed.

I'm aware of possible reversion issues with the ZZ cam. To help avoid reversion I replaced the stock Merc exhaust system with Revolution Marine exhaust, and added a 3 inch spacer between the manifolds and risers. With the Rev system as is, the pitch from the riser to the tips is pretty steep. I would guess about 30 degrees. Also, the Rev's have a small "reversion dam" built into the risers just after where the water dumps. Plus, I try and remember to keep the idle up to or over 800 rpm's. Lower when shifting. And I rev the ZZ up a few times before shutting down after low idle times and or docking. If you can offer more on the subject I'm all ears!

Thanks for the input!

Kidnova

Mark, I've read/heard that the Gen IV had a bypass in the oil pad adapter that screws on to the block. My boat is a 1995 and I'm sure the 7.4 that was taken out was the original. So, I think that would make it a Gen V. But thanks, I'll be sure and check for a valve in the screw on, and up at the filter.

Oil pressure at idle is about 45. OP at WOT is about 55 or so. I would consider that to be good oil pressure, but not high. What do you guys think?

Bill

Nordicflame

This has had me wondering about a friend of mines problem.
He just purchased a boat that needed to have one motor rebuilt with a new block.
These are HP500EFIs and when starting out and the motors are cool he has 65 lbs in both motors. When the temp comes up stabilizes the original motor drops to 45 lbs at cruise and the new one drops to 25 lbs. The 25 lbs is abnormal and I’m wondering if they could have made an error when or if they installed the bypass.
I’m not familiar with the 500EFIs oil thermostat or if they even have one but what would be the symptoms be if no bypasses (or maybe the wrong one) were installed in the new block?

Dave

Wobble

I can't answer that question, however, rebuilt blocks often are baked with the bypass valve in place, this can dramaticly weaken them. Do you have oil temp info?

Mark

Kidnova

Heat, I installed my oil temp gauge this spring. I went through last season without a guage, and had a stock 7.4 oil cooler on the ZZ502. After a hard run oil pressure back at idle would sometimes drop to +,-20 lbs. which I've heard is not uncommon. But I'm sure the low oil pressure at idle was due to the oil being too hot. After installing the oil temp gauge and now being able to monitor the oil temp, I back off the throttle when the oil temp gets to 260* or so. And oil pressure at idle is now around 45 lbs. I use synthetic oil. I think the synthetic being better at high temps is what has saved the ZZ from damage. At least any known damage.

Most, or at least allot of people don't have oil temp gauges in their boats. Might be that some would be surprised at their oil temps if they did.

I had a guy tell me "the oil temp gauge is the best $ you will spend on your boat". I believe he was right.

Wobble

Many Boat and Harley owners would be suprised by their oil temps. Hope you have looked at M-1 20w50 thread and all the great oil info by Hydrocruiser.

Mark