OMC 5.7 King Cobra overheats at high rpm.

[easter85]

I have a 1990 Four Winns 201 Liberator with an OMC 270 Horsepower King Cobra. The boat runs fine except that lately the engine begins to run hot at wide open throttle. I have had the engine thermostat changed and have had the lower unit serviced and a new raw water impeller kit installed. They have flushed the boat and it was completely checked out by Boat Town in Austin, Texas. They checked the compression etc and everything is fine. I replaced the drive belts thinking that the original belts might be slipping on their pulleys. I bought Gates belts and they sure seem stretchy. My daughter and I have run the boat at our area lake and when it begins to overheat at wide open throttle the boat begins to smell of burnt rubber even though watch the belts at high speed gives no evidence of squeeling or smoke. One problem is that the power steering pump housing covers part of the hole that you are supposed to use to put a 1/2 inch breakover bar in to tighten up the belts. I therefore feel sure that I am not getting the power steering belt as tight as it should be. I have a few questions. #1. Is a marine fan belt any different than a car fan belt? #2. Is there a quality fan belt that you can recommend that isn't as stretchy? Am I on the right track? Any suggestions would be appreciated. I don't normally run the boat flat out; but I am afraid one of my kids might not be so careful and end up ruining the engine. Thanks. Robert E.

 

[louc]

Re: OMC 5.7 King Cobra overheats at high rpm.

Two things:<br />overheating at high rpms is often caused by clogging in the risers/manifolds, this will not show up at lower rpms. So have them checked, and make sure there are no other exhaust system restrictions.<br />burning rubber smell--if not belts, a slipping coupler can cause that. Also if the exhaust system is overheating (can happen even if the engine has not totally overheated yet), the rubber tubes that carry the water/exhaust mixture overboard can get hot and smell. Start with checking the whole ex system, from manifolds to the rubber outlet tubes.

 

[easter85]

Re: OMC 5.7 King Cobra overheats at high rpm.

Thanks for the advice. I am going to have the belts checked tomorrow and then Wednesday I am going to return the boat to BoatTown in Austin for a check out of the items you suggested.<br /><br />Thanks,<br />Robert E.<br /><br />I will post what the fix eventually turns out to be.

 

[easter85]

Re: OMC 5.7 King Cobra overheats at high rpm.

Have the boat all apart right now. Marine shop has removed exhaust manifolds, and elbows. Have removed lower unit. Everything looks good and normal. As stated before we have replaced the engine thermostat 2 times and still overheats. We are in the process of replacing the engine water pump and all hoses. Have disassembled lower unit and replaced impeller etc. Have lower unit apart. Checked all water passages in lower unit. Did a "leak down" test on engine. Everything fine. Haven't been able to locate any problems at all.<p>We are getting all parts, gaskets, etc to go back together again. If anyone has any ideas I would like to know before we put it back together.<p>This boat has always been used in fresh water, stored in a storage building, and is in pristine shape and runs perfect except for overheating at wide open throttle. No smoking gun. Any ideas?

 

[McKenzie]

Re: OMC 5.7 King Cobra overheats at high rpm.

It sounds like everything is good, so the only think i can think is you might not be overheating. I've heard of alternator regulators dying and making all the gauges read higher than in actuality. I'm stumped on this one

 

[akriverrat]

Re: OMC 5.7 King Cobra overheats at high rpm.

raw water cooled engine block water jackets get blocked with silt/sand/rust cement hard crud sometimes. you didn't say but i assume the engine drive coupler was checked.

 

[McKenzie]

Re: OMC 5.7 King Cobra overheats at high rpm.

akriverrat, you could be right, the if engine coupler slips, the impeller in the outdrive won't spin as fast, thus not supplying enough water. Whats your top speed? do you hit a point with the throttle in which the boat doesn't go faster even as the RPMS climb? Those would be symtoms of a bad coupler. If it were a car, it would feel like a bad clutch.

 

[easter85]

Re: OMC 5.7 King Cobra overheats at high rpm.

Thanks for the replies. The boat still runs the same top speed exactly 50 mph. As far as the boat smelling hot but not being hot; it is getting hot. After the boat gets hot, when you bring the boat back to idle the oil pressure almost drops to zero even though the valve lifters remain quite. As the boat cools down the oil pressure comes back up. We are just doing everything including replacing all hoses in case a hose is delaminating internally and blocking water flow. If you think of anything else please reply. Maybe when we put it all back together we will have fixed it; but, I would really like to be able to say "aha!, here is the problem".

 

[Lou C]

Re: OMC 5.7 King Cobra overheats at high rpm.

Are you sure that the impeller housing is completely sealed so that it does not suck air in??<br />Also, is it possible to flow test the manifolds and risers to make sure there is no internal blockage??<br />did the mech check the water flow from the outdrive to the t-stat housing?? <br />Are they using an OMC OE manual to troubleshoot, they are very detailed and comprehensive.

 

[easter85]

Re: OMC 5.7 King Cobra overheats at high rpm.

Lou C.<br /><br />Thanks for the e-mail. Yes, they are using a Factory Service Manual; but I know they haven't had the manifolds flow tested. I know a company here in town that has that capability. They did some work for me on an airplane once. I will suggest it to them. The lower unit is definitely sealed properly with all new gaskets etc. Thanks, I will give that a run.<br /><br />Robert E.

 

[Lou C]

Re: OMC 5.7 King Cobra overheats at high rpm.

One more thing, on my OMC there is a power steering cooler in the hose that goes from the outdrive impeller to the t-stat housing, I've heard that debris can collect in these, restricting flow, so it may be worth checking.<br />About the manifolds, if the shop has any new ones that are for your engine lying around, could they just rig up a hose to the intake nipple on the new ones,see how much flow they get for a given water pressure setting, and check yours the same way to see if yours flow the same??

 

[easter85]

Re: OMC 5.7 King Cobra overheats at high rpm.

Thanks,<br /><br />I am going to print all of this out and take it to them. Maybe it will give them some idea.<br /><br />Robert E.

 

[easter85]

Re: OMC 5.7 King Cobra overheats at high rpm.

Just wanted to thank everybody for their help. Found the problem(s).<br /><br />#1. Long water hose that goes from lower unit to engine had somewhat of a "kink" in it. When removed we could see a "kink" mark. This kink would collapse in the same spot when slightly bent.<br /><br />#2. The lower unit had a loose gromet which was allowing air to be sucked in instead of water. Between these two things they caused the problem.<br /><br />Just got back from a week on Lake Austin in Austin, Texas and everything worked perfectly. Tim Harp of Victoria Marine here in Victoria, Texas took a real interest in the boat and went from stem to stern to solve the problem. I told Tim to replace everything he took off since it was all 13 years old. He replaced the thermostat, all belts and hoses, both exhaust elbows, both water pumps and several gromets, clamps etc. He also took the lower unit off and traced every water passage. $1,480 later it does work. I didn't mind the expense since the problem is fixed.<br /><br />Just as a side note. If you haven't been to Lake Austin in Austin, Texas you really are missing something. Lake Austin is like a river in that it is about 20 miles long but has a dam at both ends. The water is clear, clean, and about 68 degrees. <br /><br />There are many beautiful homes and some excellent restaurants on Lake Austin. Lance Armstrong, and Sandra Bullock have homes on this lake.<br /><br />There is an excellent RV and camping park which is owned by the City of Austin. It is called Emma Long Park or Austin City Park. The RV spaces are about 50' from the waters edge and carpet grass runs from your RV site down to the water. The bottom is sandy. I have been going there for over 20 years. It is mostly excellent except this time there was a bunch of "rednecks" in a couple of camp sites. The best time to come is before June (when school lets out for the summer)or after September the 1st when the Rednecks and their dogs and kids are back in school.