model 888 overheats@ high r.p.m.

[Haut Medoc]

I have a 73 searay model 888 (302 ford) FWC It overheats when over 1500 rpm. Real hot @wot. Will cool back down slowly @ 1000 rpm or less. Pump in OD is good. Elbows clean.( I can hold my hand on them) So I should be getting enough water through them.Took caps off Exchanger, I can see through it. Fluid level good. Oil pressure good. Thermostat new.Engine pump does not leak out of weep hole. Could a blown head gasket do this? Is there a way to check for it ? I really don't want to take it down to the heads to find out. I don't know this engine very well. It runs great by the way, Any input would be helpful.I'm stumped. I miss my Chevy. Thanks, Jeff

 

[achris]

Re: model 888 overheats@ high r.p.m.

Water pocket cover, in the bottom of the driveshaft housing (upper leg).<br /><br />Get a bit of clear hose and put it in place of the water hose coming from the inside of the transom housing to the heat exchanger. You should see solid water, any bubbles and you have a distorted water pocket cover. Have you pulled a leg off and apart before?<br /><br />Chris..........

 

[hondon]

Re: model 888 overheats@ high r.p.m.

Since you are freshwater cooled and have checked your heat exchanger ,you will now have to look at circulation problems after the exchanger.Circ pump, exhaust manis ,t stat.These are very typical restiction symtoms, so I 'd start there.

 

[Haut Medoc]

Re: model 888 overheats@ high r.p.m.

Water pocket cover? In the OD I surmise. I don't know where it is exactly, but I have the manual. I'll look it up. I'll give the clear hose test a shot. Thanks, Chris As I said, the thermostat is new, manifolds are clear, and I don't think the engine pump is bad - ie doesn't leak or make noise.Thanks, Hondon

 

[achris]

Re: model 888 overheats@ high r.p.m.

<br /><br />Item #2 is the 'Water pocket cover'. It's made of plastic and they distort and allow exhaust gas into the cooling system. Unfortunately the bolts are stainless into the aluminium housing and are a complete and utter b*** to remove. Guarantee you will break at least 3 of them. We built a jig for the job. If we managed to get one out without breaking it, we screwed the jig in and drilling the other broken ones out. If we broke all 4 (about 50% of the time) we'd work on getting a drill and 'heli-coil' into one and then go from there. Oh yea, we melted the old plastic cover out with a gas torch.<br /><br />If you haven't got a jig, verify the problem is the cover. Once the leg is off and split you can pressurize the cover and squirt a bit of WD40 on the edges and watch for bubbles, then take it to a shop that has done them before.<br /><br />Chris...........

 

[steve n carol]

Re: model 888 overheats@ high r.p.m.

ACHRIS, RE: Distortion of the water pocket cover, does this seem to present itself a problem w/raw water cooling? thanks in advance, steve.

 

[Blk-n-Blu]

Re: model 888 overheats@ high r.p.m.

J, Just because the circulating pump doesn't leak or make noise doesn't mean its working. My 898 RWC had overheat problems and the "last thing" I did to correct them was change the circ. pump. there was no impeller left in the pump (coroded away) mine didn't leak or make noise either.

 

[achris]

Re: model 888 overheats@ high r.p.m.

Distortion of the Water Pocket Cover will effect both raw cooling and closed cooling.<br /><br />The easy check for it is the clear hose trick. <br /><br />When I was servicing for a living, it was one of the things I'd check as part of the service. It's real easy to check when you have the leg apart to change/check water pump impeller. Just plug the water hole at the front of the leg and put some compressed air in the copper water tube, spray some WD40 at the edges of the cover and if it was leaking bubbles would appear. We used to have boats coming in with these 'weird' cooling problems. Usually took a few hours to get all the busted bolts out, but the feedback from customers (most of the time) was that they been living with the problem and 'nobody' could fix it. Made us feel pretty good. It's an area overlooked by a lot of mechanics.<br /><br />Chris.............

 

[MrBill]

Re: model 888 overheats@ high r.p.m.

J...Often overlooked in your set-up is the closed portion of the cooling system since most of the issues are usually in the raw water side. When the engine is cold (first start of the day..) start up with the closed cooling side cap off and see if there is circulation once the thermostat opens. Obviously you'll want to shut down or cap it shortly after confirming flow. If flow seems acceptable proceed to diagnosing the raw water side.<br /><br />But since your engine cools down when rpm's are brought down, your issue is flow related. <br />1 - How warm is the heat exchanger when engine is hot?<br />2 - If the engine is run on muffs, does it keep the engine cool enough at high throttle, if so, the pressure is providing flow that the impeller can not (for some reason).<br />3 - You should be able to isolate the problem from here to a point past the impeller...exhaust restriction included.

 

[achris]

Re: model 888 overheats@ high r.p.m.

2 - If the engine is run on muffs, does it keep the engine cool enough at high throttle, if so, the pressure is providing flow that the impeller can not (for some reason).

Don't ever run the engine above about 1200 rpm on muffs! A standard hose can't supply enough water from the pump and they 'run dry', burning the impeller.<br /><br />Chris............

 

[Haut Medoc]

Re: model 888 overheats@ high r.p.m.

Chris, the clear hose test did not show any signs of bubbles, clear solid water,so I think I can rule that out. Good idea though.Thanks for the heads up though. Mr.Bill, I have never run this motor with muffs, only in the water. The thermostat does open. I visually inspected the engine pump, The impeller looks real clean. I completely unhooked the exchanger and flushed out both sides. It doesn't seem to have any restrictions at all. I replaced starboard manifold this spring, and cleaned out the riser, I did the port the other day.The exchanger does get real hot. There is no restriction beyond the risers, right?Thanks for your input. Jeff

 

[Haut Medoc]

Re: model 888 overheats@ high r.p.m.

Is it possible for the od to pump with impeller backwards? how much water should come out with the inside boat with the water tube disconnected? I only looked at impeller condition, not position. Thanks, Jeff

 

[achris]

Re: model 888 overheats@ high r.p.m.

Jeff,<br /><br />It's normal for the exchanger to get really hot. The water is being heated by the exhaust gases. When you checked withe the clear hose, did you run it at the speed that the problem occurs , or just at lower speeds? Have you checked the ignition timing?<br /><br />Chris.......

 

[Haut Medoc]

Re: model 888 overheats@ high r.p.m.

Chris, No I only checked it at the dock. I had it tuned up by a mechanic, because I didnt want to set the points, I havent checked the timing, but it runs well, real well. Is it posible that the impeller is backwards? Will it deliver enough water in that position? At idle or @1500? It really feels right except for when it gets hot. Even then it doesn't feel bad, but i think that if I stayed on it it would get way hot. I will try it as you say , but @ 2000 rpm it didn't show it. Is it wise to run so many rpm even if it's in the water? In Neutral? J. Thanks

 

[Haut Medoc]

Re: model 888 overheats@ high r.p.m.

Chris, No I only checked it at the dock. I had it tuned up by a mechanic, because I didnt want to set the points, I havent checked the timing, but it runs well, real well. Is it posible that the impeller is backwards? Will it deliver enough water in that position? At idle or @1500? It really feels right except for when it gets hot. Even then it doesn't feel bad, but i think that if I stayed on it it would get way hot. I will try it as you say , but @ 2000 rpm it didn't show it. Is it wise to run so many rpm even if it's in the water? In Neutral? J. Thanks

 

[achris]

Re: model 888 overheats@ high r.p.m.

Jeff,<br /><br />You'll need to check it under actual operating conditions. The reason is that the exhaust gas only get into the water under pressure. That pressure is generated by LOTS of exhaust, like when you're at high rpm. It's a bit of a fight between the water pressure and the exhaust pressure, whichever is higher will run into the cooling system.<br /><br />If an old impeller was installed backwards the blades would fold back over to run the 'right' way. The problem that causes is the blades will eventually break off. I usually avoid that problem by replacing the impeller everytime. Cheap insurance.

 

[Haut Medoc]

Re: model 888 overheats@ high r.p.m.

Chris, It doesn't have get bubbles at operating temp. either. I'm convinced that the problem lies elsewhere. I was looking at some of the Mercruiser manuals from my old Chriscraft . In the mechanical over-heat section it says that a blown headgasket will cause overheating at high rpm. I really think I've done all I can with regards to circulation and need to look elsewhere. Thanks for your input though. Jeff

 

[achris]

Re: model 888 overheats@ high r.p.m.

Jeff,<br /><br />You have closed cooling. If the head gasket was blown you'd see bubbles in the 'radiator'. Or if it's blown across 2 cylinders, that would show up on a compression test.<br /><br />Please keep us informed, you've got my curiosity up now <br /><br />Chris............

 

[steve n carol]

Re: model 888 overheats@ high r.p.m.

J.kopec, <br />"you will now have to look at circulation problems after the exchanger"<br />Sounds good to me. <br />today, I located a cooling hose that was de-laminating, on the inside. <br />Don't think you mentioned actual temp. at WOT. <br /><br />Gauge correct? Touch method? wish you the best. sl<br />have a great 4th "only in America!!"

 

[Haut Medoc]

Re: model 888 overheats@ high r.p.m.

Chris, There are a few bubbles at idle. I never took the cap off when its real hot / 185 degrees, I know that this is not super hot, but I can tell that it would just get hotter if I stayed on it. And I ain't gonna go there. I will certainly keep you posted. Thanks, Jeff