motor over heating? help

[grzzzz]

I have just restored a 66 starcraft Holiday 18'. Have been working on it several years. Finally got to to the lake this year. Been out 3 times. It is a 110 hp Chevy iron duke, Mercurser. That's what the sticker says.... Bored out max, new pistons, machinist enlarged the valve seats, says he put in 302 valves that fit nicely, cam from a duke generator that has a slight "lift". Carb rebuild for elevation, (I fish lakes over 8000') So that is what I am told...and paid for.

So, launch and motor to the fishing spot. Runs about 160 degrees on mechanical gauge. Has a 140 thermostat in it. Drop my rude 9.9 and fish all day. Start the 110 and get about 100 yards and it spikes to 200 and starts cutting out.... sign it is really getting hot.

Taken it to 2 different marine mechanics so far. (plus what I did) They just keep doing the same thing (what I have already done) and charge me 300 bills. Dump it in the lake and ...same thing.

So far between what I have done and have paid to have done;
Thermostat.... twice
impeller ..... 3 times
water pump .... twice
pick-up tube ... once
motor.... less than 3 hours on it. Completely disassmenbed, boiled out.
all new hoses, connecting lines from out drive through engine.

Any ideas?

Grzzzz

 

[boatnut74]

Re: motor over heating? help

Have you checked the oil to see if it was milky? Since you replaced all those other parts I would suspect you have a cracked blocked. Have you hooked it up to the muffs to see if you have water coming out the prop? If not you may have a blockage somewhere.

 

[TheWrks]

Re: motor over heating? help

Mine started to overheat! it turned out that the intake hose from the O/D to the engine (located port side of the bellows in the Gimble housing) was too long and this caused a kink in the hose thus restricting the water flow....

Scott

 

[Pugetsound]

Re: motor over heating? help

Sounds like you found my 120 engine that I spent over $3000 in a period of three years and finally sold the boat. Is the boat raw water cooled or fresh water cooled. If there is a heat exchanger it may be restricted. Or EX. Manifold plugged. Seems strange it ran ok and the all of a sudden acted up. Never able to get my aglasply to not overheat. Some mech say the 120 GMC will run hot and thats ok.

 

[grzzzz]

Re: motor over heating? help

Boat nut
No water in oil. Motor professionally rebuilt 3-5 hours ago. Block boiled and mag fluxed. I cleaned, polished and painted all bolted on parts. Went as far as polishing all the passages in the manifold I could reach. I KNOW all passages are clear. Mechanic ran it for an hour in the shop with muff. I ran it about the same amount with muffs and in a tank. Only heated up after it was shut down for a while then restarted.

Scott
I replaced all hoses and connection when I put on the rebuilt drive. All bellows too. I cut all hoses to match the old ones. But.... doesn't mean the old one was right. Odd though that it will run cool as long as I want till I shut it down on the lake. You would think if it was the hose kinked, it would run hot all the time???? But thanks ... I think I read your thread before and looked at that.

P-sound
Raw? Fresh water? sounds like the same but has no cooler. Sucks right out of the lake, that is in the 60s now in most lakes I go. Blown air through it, sucked water through it. Seems to blow and flow fine. Runs fine leaving .... hates coming home.. Hmmmm just might be the perfect boat after all!!!!

Thanks

 

[CheapboatKev]

Re: motor over heating? help

Any chance you have checked the water passages in the outdrive as well as the water passage at the gimbal where the OD mates to?
When I was putting my OD back on after changing the impeller, I happened to notice those passages were dang near closed from sand and calcium deposits

 

[grzzzz]

Re: motor over heating? help

Thanks Cheapboat

But, motor, outdrive and complete gimbal assembly, has been broken down to the last nut and bolt over the last 3-4 years of restoration. In most cases, not only were the passages/ports cleaned but where I could I polished them. The boat has only been in fresh water, not saying fresh water cannot corrode.

Thanks for your thought
Grzzzz

 

[scoflaw]

Re: motor over heating? help

Not sayin this is your problem but, bored to the max will create more heat. A cam with more lift will increase compression which = more heat. The pistons you used might be giving you more compression as well. Back some timing out of it, and give that a shot.

 

[grzzzz]

Re: motor over heating? help

Thanks for replying with your thoughts, scoflaw. I will try that but, I can run it all day with muffs or tub. On the lake, it has constant 60' water running through it, 140 stat. Leaving the dock, I can run full out endless. But, shut it down for a period and re-start it and ...... within 100yrds spikes to 200 and begins to cut-out?

Thanks again! I'll give it a try.... done everything else!

Grzzzz

 

[scoflaw]

Re: motor over heating? help

sticky stat?

 

[CheapboatKev]

Re: motor over heating? help

Hell....
Run her without a Tstat briefly and see what happens..

 

[grzzzz]

Re: motor over heating? help

I am going to try that this weekend. Without the stat...... what could restrict any flow? The stat i have in there now is the second one, third if you count the one it came with. Could a man be so unlucky as to get the 3 defective stats out of a million made? Silly question..... of course I could!! LOL! A guy off line told me if that does work try drilling a small hole in the stat before putting it back in. The stat will still function but air/steam will not build up behind it and cause a "lock" ????? At this point, trying any suggestion. Please keep them coming!

Grzzzz

 

[CheapboatKev]

Re: motor over heating? help

It is a marine stat right?
Look fwd to hearing what happens

 

[grzzzz]

Re: motor over heating? help

Got it from a marine parts place... Thanks, look for mail Monday!! Wish I could figure out how to attach pics. The boat turned out quite nice.

Grzzzz

 

[grzzzz]

Re: motor over heating? help

Went to the lake..... fixed the over heating problem but not sure how/why!!! Immediately started getting hot pulling from ramp. Started trying things!! Grabbed the upper heater hose with channel locks. I always suspected it was the water by-pass that relieved the pressure from the impeller before the thermostat opened. The temp immediately began to drop. Could actually watch it drop on the gauge. Down to 130!! Duct taped the handles of the channel locks together and the motor ran cool all day!! Obviously the water was going right out the by-pass (if that is what it really is) and not into the engine. Stopped by the boat mechanic and showed him what I did. He said just block off the hose and go for it!!! Not sure I should do that? It was put on there for a reason. Will I blow out the impeller? Something worse?

On top of that "cavity" where the inlet hose and by-pass hose(?) is there is a check valve(?). According to the book, when you remove that there is a spring there. Well, I have no spring in mine. Tried all last Fri and all my regular parts places say it is no longer available.... Could it be that simple....a missing spring? Can I just go without it and block off the by-pass?

Thoughts!!

grzzzz

 

[grzzzz]

Re: motor over heating? help

Narrowed it down to the relief valve on the top of the manifold. Per mercury there were 2 types on the old 110hp motors. A spring and stopper type and the stand pipe riser type (the one I now have). The stand pipe seems to be the newer of the 2 so should be working right. It raises the water level in the manifold above the water pump level inlet so should work under any conditions, but, for some unknown reason the lake water flows right out the by-pass and not through the engine. If I block off that by-pass outlet, the motor cools right down and runs perfectly!! Is it possible I bought the 1 in 100,000 new water pumps that is defective? Certainly I could have!!! I have searched the world over and found all the parts to the old style check valve with the spring and stopper. A more positive check valve. Should I pull off the stand pipe and put the old style knowing that if THAT worked it probably woul not havbe been superseeded. Pull off the water pump AGAIN and verify operation? Anybody ever have any experience with these valves? Ideas?

Grzzzz