Dirthead

I hope you might be able to provide some advise. I have a 1995 272 Islander Baja with a carbureted Generation V Merc 454, with a Bravo 1. Rebuilt the engine 2 years ago (got hot and cooked it). While rebuilding it, we put Aluminum heads, Lighting headers, roller cam, bigger carb, good pistons, rods, ect. The bock was magniflexed, and everything was fine. Basically built some more power, but with the real intentions of improving the reliability.

I have had the boat out twice this year. Each time when I am at WOT for about 2-3 miles, 62 MPH, 4900 RPM, the water temp climbs to 210. Water pressure is at 22-25, Oil temp at 140, Oil Pressure is 60 PSI. The water temp may limb more, but when I see it at 200, I idle down and watch the temp drop back to 160. In an attempt to fix the problem, I replaced the seawater pump housing and impeller (there is no circulation pump and this is in fresh water only) and did not find any missing rubber pieces. I also replaced the 140 marine thermostat for a 120 marine thermostat. These changes did not fix the problem.

2 year ago, I replaced the water inlet hose that goes over the top of the lower unit and back into the boat (this had a kink in it and is what caused the first engine to cook) so this hose is fairly new. The oil cooler is not plugged and at idle I have plenty of water dumping out my water bypass. When the engine gets to 210, the Lightening headers are still cool to touch. The oil has no water in it. The lake water temp in Iowa has only been 72 degrees.

Where would anyone start to look? I have thought about removing the thermostat and plugging the crossover hose (the hose that goes from the old circulation pump to the thermostat housing) but have not done that yet. I am just afraid of cooking another engine! Please any advice would be appreciated!

Bajapred

iTrader: (1)

I think on that year motor there are two oil coolers...MAKE SURE THEY ARE OPEN....you will have to remove them and dig any debris out of them..it will not just fall out and prob not even backflush out, this is my first guess for your problem...however, you could be sucking air through your transom hose if it is not properly sealed...this type of symptom you are describing is typically a water flow issue..works fine at low rpms but when engine is running hard you have a high heat problem....btw..I would not run it for 2-3 minutes anymore @ WOT until you have found and fixed this problem...basically you need to track from your seawater pump all the way around and clean anything the water goes through all the way to your front crossover, you say you changed your t-stat so that area is already checked I guess...good luck

Dirthead

This boat only has and I am pretty sure that it only came with 1 oil cooler. I can not find any retrictions in it.

hoozeyurdaddy

you and I need to talk and compare, I a'm running a 622 naturally asperated with CMI big tubes and a crossover, I a'm having very simular problems, 10psi at idle and 35 at 4000. with a standard 160 thermo it will over heat, Does your crossover dump into the top of the thermo housing?
as of right now I have drilled 4 1/8" holes in the thermostat so the water could pass, it's keeping the engine cool but is not the awnser to the problem, I think the water coming into the top of the thermo housing is cool enough to not let the stat open properly. feel free to call me. 435-820-0377
larry

Dirthead

Larry,

I will try to give you a call later today. Yes, my crossover dumps into the top of the thermostat housing. I have never thoguth of that, but at the thermostat housing having the crossover inlet, two outlets to the lightening headers, maybe the thermostat is not opening up.

Whaqt are your thoughts on plugging the crosover hose that feeds the thermostat housing and removing the thermostat?

NightHawk

Check the inlet hose adapter that attaches the inlet hose to the inside gimbal ring for debris or restriction. Comes off with two bolts. This has been know to cause similar problems in the past on that motor.

Dirthead

I can get the adapter off of the boat, but see no way to be able to look into the fitting that comes through the gimble adapter while the engine is in the boat. Any suggetions here?

baronbob

Perhaps I am confused here but my crossover has eliminated the circulation water pump like I assume yours has and therefore my cold water inlet is plumbed into the block at this point. I have no cold water into the thermostat housing as you describe. The cold water is forced into the block through the crossover, then travels through the heads, through the intake to the base of the thermostat, where Procharger calls for the drilling of three 1/4" holes to allow for minimal water passage while the thermostat is closed. My cold water inlet does not pass through the thermostat housing. It direct connects to the crossover, as without the circulation pump, pressure is needed at this point to force cold water through the block. In the stock system you always had water going through the block as a result of the circulation pump (no longer there). What might be happening to you is that if you are passing the cold inlet through the top of the thermostat housing while the thermostat is closed the water is in fact forced through the crossover into the block but has no outlet until the thermostat opens or has a couple of holes. once the thermostat heats up there is no pressure differential to effect flow and no circulation through the block therefore no significant cooling. Solution!! plumb the inlet through the crossover and drill (3) 1/4" holes in the thermostat these handle overflow to the headers/dump during warm up. I will bet this will work as it does on my 500+HP application. If you are not as confident, direct connect to the crossover, take the thermostat out prior to drilling the holes and she should run so cool the gauge may never lift off the peg. Oh yes and do plug the current inlet on the top of the thermostat housing. My Mercruiser service manual has a flow diagram to support this idea. The small hose connection previously returning to the circulation pump from the top of the engine should have been eliminated with the initial crossover installation. You can call if the above has totally confused you Bob @ 530 587 4700

hoozeyurdaddy

if you called yesterday, sorry I missed your call, I will be in town all day today, so try again. 435-820-0377 or 435-637-3304, from the way it sounds we are having the same problem. I tried removing the thermo, your engine will build up no temp and thats not good.

baronbob

If you are refering to my suggestion of temporarly removing the thermostat, the next step is to drill the holes and put it back in. Does what I suggested make sense for Hoozeyurdaddy?