1987 5.7L 350XL Fuel Injected

Have twin 1997 Crusader 5.7L 350XL fuel injected engines with 708 hours on them, port engine runs fine with no issues but the starboard engine will not run as it has bad compression on cylinders 3 and 5 nor will these two cylinders hold compression. Both engines power twin V-drives, engines are set in boat with flywheel/output facing forward to the bow. The boat is a 1997 Cruisers 3075 Rogue Yacht, looking for advice as to what I should do with the starboard engine, what rotation would it be and if 708 hours is excessive enough to go ahead and pull both engines for rebuild before this years boating season starts.

Welcome to ME.com!!

A leakdown test will give you insight to the cause of the compression leak. Being adjacent cylinders have issues, could be head gasket....

As far as rotation, the Serial Number Plate is your best source of those details....as long as the engines are original.

700 hours should be ~ 35% of the life of the bottom end, assuming decent maintenance has been done.....the top end typically sees 1000 hours before needing to be reworked.

If Raw water cooled the engine blocks are at the end of their life span for time, not running hours....If they are FWC, Like MakoMark says, do a leakdown test.

I would do a Leakdown on both engines, then you will know their true health.

As far as rotation I thought that by 1997 GM had done away with reverse rotation.

I think the introduction of Gen VI was the end of GM's standard production reverse rotation offeings....that said, there's always some inventory that needs to be consumed before the 'new' products actually make it to the end user....so, I wouldn't be surprised to see a few RH Gen V bigblocks in the 1998 serial number span.....

Leak down test shows leakage in top and bottom of Stbd engine, pulling it for a complete rebuild shortly. Also checked Port engine with same amount of hours and the results were questionalble as to re-build or not. Now pulling both engines to keep them both at same intervals is best decision, both engines pulled and rebuilt in 10 days doesnt seem too long.

Update on starboard engine, one last attempt at diagnosis before pulling engine to save time and labor. Head gasket on 1,3,5 and 7 was bad, had a open area between 3 and 5. Replaced head gasket and engine will start up easily and idle, exhaust manifolds were getting hot 180 range so I shut off engine and allowed to cool for a period of time. Checked coolant at thermostat cap, coolant was not visible so began to fill with 50/50 mixture and it took 1.75 gallons to fill to top. After starting engine again at idle rpm for 5-8 min I noticed the exhaust manifolds were beginning to get hot again. Checked coolant level again and once again its not visible. No evidence of coolant in bilge or in the oil, collected water from exhaust into clear container to see if coolant was escaping through exhaust. Exhaust water was clear after allowing to sit couple min, was kind of white at first. What temp should exhaust manifolds be at idle, using a laser thermal gun to measure. The cooling system is "Full Fresh Water Cooling"

The exhaust manifolds are cooled by the coolant leaving the thermostat....so in steady state, they will be as hot as the temp the gauge indicates. Usually, the outlet (tops) will be hotter as the coolant absorbs the heat in the manifolds.

The riser/elbow is cooled by the water leaving the HX....you should be able to put you hand on them though not for long..

If the coolant isn't going into the crankcase, it has to be leaking out (hose clamp/fitting loose) or it is leaking out the exhaust. I'd suggest a pressure tester on the cooling system and checking all the hoses again. the HX could also be violated and that leak usually goes into the risers..

Collected water from exhaust while engine idling, water looks good and clear. Would a litmus paper test work to see if coolant is diluted in exhaust raw water?

I don't believe litmus paper will give you any indication of the coolant's relative concentration....only a nominal pH value....

a pressure tester with the exhaust hose removed from the elbow is the most definitive test i can define....not easy but very revealing..

how hot should the exhaust maifolds get at idle? all of the colling lines are original 1997 and when I check the larger 1.25" hoses by squeezing them they feel as though there are large areas/sections that feel hard/crunchy. I assume this is because steel reinforced hoses but for some reason feels odd.

If the 1.25"ID hoses are original, I'd think they are ready for replacement.....

The factory hoses are reinforced so the 'hard feel' is normal....the crunchy aspects isn't.

Thanks for the input, my thoughts exactly on the crunchy feeling. Another point I noticed was on the Starboard engine thru hull bearing seal there was water coming out at the thru hull around bottom of shaft. Not so on the Port engine, thinking something was wrong I did some reading and both the port and starboard thru hull bearing are raw water cooled and once I was able to get myself down in between engines I could see the water line on a fitting at the bearing on both port and starboard. So I assume water coming out of the starboard was a good sign but with no water coming out of the port side bearing is this a bad sign?

I think you are talking about the stuffing box...thur hulls are for water.

Typically, on a traditional stuffing box, the packing gland is tightened for a 'slow drip rate' with the shaft rotating......a few drops per minute.....the big thing is to make sure it doesn't get hot with the boat up on plane.....also, there should be no significant drip with the shaft idle.....

The newer 'dripless boxes' dont drip....they typically are cooled via an injection port, usually fed from the raw water cooling the engine.

Mine must be the newer "dripless boxes" because there is a water line from raw water circuit going down to the seal/bearing for cooling according to manual but it doesn't call it "dripless" it still reads that so many water drops per min is normal. Also this is a 1997 no 87 which was a typo, so Port engine not having water flow at this bearing is an issue. Has nothing to do with starboard engine issue but never the less something else that needs attention.

I'd suggest getting the details from the hull maker and then contact the 'stuffing box' OEM to get their recommendations...