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93' OMC 5.0 EFI - Struggling with hot starts, sagging drive and overheating at idle.

C

cameron.oneill92@hotmail.

New member
Hey everyone,

Just picked up a 1993 Four Winns Horizon 210 with the OMC 5.0 EFI. Overall the boat looks solid and the motor runs strong, but I’m chasing a couple issues and could use some advice.

I’ve already replaced the thermostat and anti-siphon valve, and compression is good across all cylinders. The main problem is it overheats at idle — on muffs it’s fine, but in the water it creeps up and I have to rev it while in neutral to bring the temp down. Once it’s moving it cools off okay. I've ordered upper drive unit seals and gaskets.

Also, the drive sags back down to the ground after about 10 minutes whether I’m idling or cruising. The trim pump still works and lifts it fine, but it won’t hold position. No obvious leaks from the cylinders. Ordered new trim cylinder rebuild kits.

On top of that, hot restarts have become a real pain — it cranks forever before it fires, especially after it’s been sitting for a bit. Thinking fuel pressure regulator? But not sure.

Any help is appreciated!
 
Overheat at idle, replace the water pump impeller and see if the pump housing also needs replacing

Drive sagging, means the trim pump or trim cylinders are leaking, need rebuild, most likely it's the cylinders

Hot restarts, do testing. Check fuel pressure, look at the plugs, cap, rotor. What were the compression numbers?
 
AllDodge said:
Overheat at idle, replace the water pump impeller and see if the pump housing also needs replacing

Drive sagging, means the trim pump or trim cylinders are leaking, need rebuild, most likely it's the cylinders

Hot restarts, do testing. Check fuel pressure, look at the plugs, cap, rotor. What were the compression numbers?
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I replaced the impeller and housing. Also cleaned out the power steering cooler and there was a few small chunks of impeller but nothing crazy. Still have the issue.

Will rebuild cylinders and hope that fixes the sagging, parts are on order.

Compression was around 140-150 per cylinder if I remember correctly (cold)

Plugs are all new, rotor cap is new. What am I looking for when looking at fuel pressure and the cap and rotor?
 
I replaced the impeller and housing. Also cleaned out the power steering cooler and there was a few small chunks of impeller but nothing crazy. Still have the issue.
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My guess is your sucking air somewhere

Get some clear tubing from the hardware store, double barbed fittings and hose clamps. Make some short pieces of the clear tubing and place them inline with intake hose to thermostat and other areas. If you see bubbles when in the water your sucking air

Those are good compression numbers if your ,memory serves

What am I looking for when looking at fuel pressure and the cap and rotor?
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Cap and rotor has nothing to do with fuel pressure
What is the fuel pressure when running at the throttle body (TB)?
 
When shutting off a warm engine (as when you expect to have the hot start issue....)....
Remove the flame arresting & look down into the throttle body. Do you see any fuel dripping? If YES, your fuel injector is leaking & flooding the engine. As the fuel leaks, residual pressure drops & leak eventually stops.

Alldodge asks directly above what the fuel pressure is. Check that & watch if it leaks down when shut off.
 
Circulation pumps on engine rarely fail (maybe leak/drip but still pump ok) in fresh water BUT I don't know where he is.
 
Droid said:
Circulation pumps on engine rarely fail (maybe leak/drip but still pump ok) in fresh water BUT I don't know where he is.
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my engine started running hot at idle in water or on hose
changed impelller an did flow tests by passing it.
water pump on engine was original with 860 plus hrs ALL fresh water. in fact the #2 eng gets her new one in fall layup
it was missing several fins and was not moving water very well
at speed on plane the pressure flow from the lower unit feed kept engine cool
its an easy thing to look at with a borescope
 
cameron.oneill92@hotmail. said:
Hey everyone,

On top of that, hot restarts have become a real pain — it cranks forever before it fires, especially after it’s been sitting for a bit. Thinking fuel pressure regulator? But not sure.

Any help is appreciated!
Click to expand...
Open the throttle a bit next time it has a hot start problem. If it starts easily, check the resistance of the ECT (Engine Coolant Temperature) sensor- if the resistance is too high, the ECM will deliver more fuel than needed because the resistance and temerature have an inverse relationship. This sensor has two wires- one yellow, one black. The one-wire sender is connected to the gauge.

1784390486250.png
 
Are you using an OEM OMC impeller kit? Did you replace the wear plate? If scored even a new impeller won’t pump right. When replacing the Cobra impeller I like to leave the plastic cover that goes on the rear of the upper gear housing off temporarily when running it on the water hose as a test. There should be no leaks around the impeller housing. If so that oring gasket may have shifted when it was installed. I use a thick grease like OMC Triple guard to hold it in place.
The other thing that can cause problems when you’re up on plane is the plastic fitting in the pivot housing for the hose that goes to the transom. These can crack if not drained or filled with AF for winterizing, then you’d be sucking air. Same with distorted water tube grommets inside the drive. They can get distorted from a past overheat.
Lastly make sure all the passages in the thermostat housing are clear. They get clogged with rust just like exhaust elbows.
 
louc said:
Are you using an OEM OMC impeller kit? Did you replace the wear plate? If scored even a new impeller won’t pump right. When replacing the Cobra impeller I like to leave the plastic cover that goes on the rear of the upper gear housing off temporarily when running it on the water hose as a test. There should be no leaks around the impeller housing. If so that oring gasket may have shifted when it was installed. I use a thick grease like OMC Triple guard to hold it in place.
The other thing that can cause problems when you’re up on plane is the plastic fitting in the pivot housing for the hose that goes to the transom. These can crack if not drained or filled with AF for winterizing, then you’d be sucking air. Same with distorted water tube grommets inside the drive. They can get distorted from a past overheat.
Lastly make sure all the passages in the thermostat housing are clear. They get clogged with rust just like exhaust elbows.
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Sierra kit with housing and plates for the impeller. I'll look to see if it's leaking at all next time I run it on muffs, didnt think of that but that oring was a bit of a pain.

The overheating issue doesn't seem to happen at all on plane or even moving a few knots at 12-1300 rpm - good temps. As soon as I have to dock or idle in to the ramp it starts climbing.
 
jimn said:
Open the throttle a bit next time it has a hot start problem. If it starts easily, check the resistance of the ECT (Engine Coolant Temperature) sensor- if the resistance is too high, the ECM will deliver more fuel than needed because the resistance and temerature have an inverse relationship. This sensor has two wires- one yellow, one black. The one-wire sender is connected to the gauge.

View attachment 37522
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I'll have a look into this, thanks!
 
If all else fails order an OEM impeller kit & housing right on this website; I use them for OMC parts all the time….
Don’t mix and match parts either. If you have a OMC impeller housing use only an OMC impeller and same with Sierra. Mixing one with the other can cause problems
 
Fixed the power steering leak, it was frayed hose at the power steering cooler. Found it using UV dye. Cut about a quarter inch off and no leak since.

Fixed the overheating issue at idle. When I split the upper and lower units, the copper tube grommets were dried out and split. Replaced those as well as the gaskets on the housing for the water intake. Now I have a problem where it's cooling too much at idle but I'd rather have that issue than overheating.

Rebuilt the trim cylinders and they worked for a day but then started leaking down the next day after I took it out for a boat ride.

On my last ride out after fixing the overheating problem, the engine didn't have any issues restarting hot as it was never that hot. Wondering if it was a sensor not allowing the motor to start because it was too hot
 
cameron.oneill92@hotmail. said:
Fixed the power steering leak, it was frayed hose at the power steering cooler. Found it using UV dye. Cut about a quarter inch off and no leak since.

Fixed the overheating issue at idle. When I split the upper and lower units, the copper tube grommets were dried out and split. Replaced those as well as the gaskets on the housing for the water intake. Now I have a problem where it's cooling too much at idle but I'd rather have that issue than overheating.

Rebuilt the trim cylinders and they worked for a day but then started leaking down the next day after I took it out for a boat ride.

On my last ride out after fixing the overheating problem, the engine didn't have any issues restarting hot as it was never that hot. Wondering if it was a sensor not allowing the motor to start because it was too hot
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If you run it normally/somewhat hard and shut t down, wait about 5 minutes before turning the key to ON (not crank). After that wait, check the temperature, but don't freak out when you see that it's around 200°F- it's normal, caused by heat soak (the heat lost by the hottest areas, gained by the cooler areas). If it's higher than 200°F, find out what constitutes 'overheat', according to the ECM's program. It's possible that the programmed 'overheat' temperature IS causing it to not start as a preservation move. If you open the engine cover and turn on the blower to let it cool, it's likely that it will start once the temperature drops below 190-ish.

If the sensor fails, its resistance will be higher than normal, causing too much fuel to be delivered- if its resistance is normal and tells the ECM that it's too hot, it's not a problem. In areas like the Desert SW of the US and other places, heat soak DOES prevent normal starting- if you're in that kind of climate, you have a few choices- let it idle for a couple of minutes before shutting it down, so it will cool. Open the engine cover and use the fan to cool it. It's a good practice to let the engine cool before shut down in any climate, really.

You probably won't find anyone who can reprogram the ECM, but if you do, have the overheat temperature raised- I wouldn't raise it much.
 
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