5.7 OMC Engine Problems

[tom Carlson]

I have a 1988 Four Winns Vista 245 with a 5.7 OMC engine. Last year the engine overheated due to a bad impeller. The impeller was replaced and everything seemed ok. This season I noticed the boat was running hotter 200 degrees when I ran the engine at 3500 to 3800 RPM. Once I slowed down to 1000 RPM the engine cooled to 165. I?m running the boat in Lake Michigan so the water is pretty cold compared to lakes down south. I also noticed that the oil pressure dropped to 20 pounds when the engine got up to 200 degrees. A few minutes after the engine temp drops to 165 the oil pressure begins to go up. I?m assuming the oil is thinning due to the engine temp at 200 degrees. The engine also does not seem to have the get up and go it did before the overheat.

What is the normal running temp for this engine? I checked the oil, no water in the oil. Could this be a blown head gasket(s) or warped head(s)? Any tests I can do prior to ripping down the top end of the engine or worse the hole engine? Would the oil pressure drop due to the heat thinning the oil?

 

[norowing]

Re: 5.7 OMC Engine Problems

Hi Tom,
I'm no expert but I have a lot of hands on with this type of setup, I rebuilt mine myself and experienced the same trouble. My engine does the same thing when it overheats as yours (oil pressure drop). The very first thing I would do is get the boat back in the water and make sure you get a good stream of water coming from the impeller by removing the supply hose from the t-stat housing. If its not good and strong remove the hose at the inlet of the power steering cooler and check again. That little tube is notorious for clogging with crap. If you've got good water presure then I would check and or replace your t-stat. If you have bad water pressure I would recheck the impeller. As you may know never ever run your engine out of the water without earmuffs and don't rev it above 1500 rpm on muffs as this will burn up your new impeller.(don't ask how I know). As far as performance the first thing I would check is cylinder compression. Good Luck.

 

[jtybt]

Re: 5.7 OMC Engine Problems

Pretty sound advice if you ask me.

 

[tom Carlson]

Re: 5.7 OMC Engine Problems

I checked the flow from the outdrive and the water stream is strong. To be safe I changed the thermostat and checked the flow of the cooling pump which was working good. The next step will be to do a compression check.

I'm just happy I have a large area to work on the motor.

Thanks for the help.