1987 OMC V4 Runnin Hot but Why??

Here is the drill: I have twin 1987 OMC 1.6L V4 SeaDrives on a 23' Wellcraft CC. I put it in the water today and futzed around for 20 minutes or so at no wake speed. Go to put it up on a plane and as it is climbing the step the starboard motor reves up to 5000 rpm, the port to 3000 rpm. When it gets up on the step the stwbd to 5500 rpm - the port to 4000 rpm - - after maybe 15 seconds the overheat horn goes off on the port motor. I shut it down and putzed back to the ramp on the stwbd motor (thank God for twins).<br /><br />Now the background - I run pre mix having the VRO removed when I got the boat 9 yrs ago. Water pump was replaced on both motors a year ago - water pressure on both motors at idle is 10 lbs and when on plane (for the short period before the horn went off) both motors were at 20 lbs. Good water flow from the telltale on both motors. Replaced the thermostats on both motors 6 months ago.<br /><br />Spark tested OK and compression tested (110 lbs +/- 5). Timing recently adjusted. New plugs & wires on port motor since last run. Cleaned & rebuilt the carbs on port motor this weekend. SS props with no nicks or bends.<br /><br />I fresh water flushed both motors (I run in salt water all the time) when I got home and nothing seemed out of the ordinary.<br /><br />I called the mechanic I use when I'm stumped & he wants to meet me this week on the water for some tests. He mentioned timing & a leak down test (I don't really understand what that is).<br /><br />Any ideas on what is going on or suggestions?

Re: 1987 OMC V4 Runnin Hot but Why??

Hey SoLittle<br />Except for the overheat, I hope you're 4th was enjoyable.<br />I don't know what you're wrench iz gonna charge you, but for about $80, you can buy a non-contact thermometer and find out if the engine is really hot or not. I bought mine at NAPA and it's one of the best diagnostic tools I have. It'll not only tell ya if the engine is really hot or not, it'll tell you which cylinders are firing or not. You just point the thing, pull the trigger, put the laser dot on the spot you want the temperature of and there it is. You may have a shorted sensor wire, a defective sensor or it might really be hot.<br /><br />g'luck & c/6<br /><br />Hooty

Re: 1987 OMC V4 Runnin Hot but Why??

Hi solittle...<br /><br />Ditto what Hooty said. With the difference in rpm, and if they generally run the same "normally", could be your dropping a cylinder at load on the port engine. With two rigs like this side by side, may be hard to hear if you are. Maybe give the ignition system the once over statically and under power.

Re: 1987 OMC V4 Runnin Hot but Why??

Thanks guys - So far<br /><br />Hooty - Gee I would like to get one of those heat guns but am going to have to think a bit before I lay out $80 for a one time use tool - not sure how I would use it out on the water though. Also I have tested the heat warning buzzer and it is OK. If it were a false positive buzzer that does not account for the difference in rpm.<br /><br />OutboardJim - Interesting dropping a cylinder under load. That might account for the 1500 rpm difference but not the heat buzzer going off. Anyway how would I test the ignition system under power?<br /><br />Catch 22??<br /><br /> Also damn right about trying to listen for what is going on with one engine when both are running.<br /><br />Anybody care to add their pearls of wisdom?

Re: 1987 OMC V4 Runnin Hot but Why??

Twin engines aren't anything I have much experience with but I seem to recall reading here about the necessity of having toe out for the alignment of the twins. You might investigate whether one engine is interfering with the flow on the other. That might account for the overheat as well as the rpm difference. Just a thought.

Re: 1987 OMC V4 Runnin Hot but Why??

are you certain you have an "overheat" ? There are 4 causes of a warning horn. 1) overheat 2)fuel restriction 3)low oil in the reservoir 4)no oil in the VRO pump. You may have a fuel restriction. It only comes on at higher speeds, & may also be the cause of the loss of power. Since you have alreadt bypassed the oil system, its not likely that the horn is related to that.

Re: 1987 OMC V4 Runnin Hot but Why??

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