Need some engine help

[Ryno23]

2nd time in a row now. Took the boat out and it over heats at low speed. I took it to the marina the 1st time it happened they changed the water pump and thermostat they told me it was fixed.

So I took it out today...bam right off they bat when at trolling speed the temp shoots WAY up to smoking hot but when I kick it in it cools right down at higher speeds.

Doesn't make sense to me. Going to take it back to the marina but was wondering if anybody else has experienced this that could guide me to a fix.. sucks driving all that way wt friends and end wt an egg.

Its a sport craft fisherman 250. OMC I/O 5.7. First time I've had trouble wt my boat since I bought it 5 years ago.

Thanks in advance.

[blueghost1]

Something in the water intake? Impeller? Zebra mussels can grow in the water systems I have heard. Just a guess, prob get better answers but where I would start.

[Sk8man]

It does sound as though something is between the intake and the pump and at low speed it is being fully blocked and then opening up under speed.

[rolmops]

It is time to completely check the cooling system for blockages. It may also be some crap around the thermostat or the thermostat itself. Personally I think that your water intake is blocked or clogged.  When you go at high speed ,the water is forced in at a greater pressure while at low speed just your pumping created vacuum is not strong enough to suck the water past the blockage.

Edited August 10, 2014 by rolmops

[Ryno23]

Thanks guys. I'm no boat mechanic that's for sure. I will look to see how to take it apart.

Wonder why the marina didn't take it apart when I took it there to see if I had a blockage. Instead of just changing parts to change them.

[bluewater]

I just had a similar problem my engine is an omc as well it ended up being the exhaust elbow after everything else was checked. On mine before the water exits the engine it goes thru the exhaust elbow thru water ports and mine was plugged solid with rust.  Not sure if your engine is like mine but I would check that if it is.

[Sk8man]

I think rolmops might have nailed it....sure sounds like it.

[Firechief48]

I had that exact same problem a few years ago and it was the impeller. Like was said could be blockage at or inside the intake. Either way water is not getting to the pump and should be easy fix.

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Edited August 10, 2014 by Firechief48

[Knotlost Charters]

When you slide the lower unit up its possable to kink the line that feeds the motor. Guess how I know.

[Patriot]

Try replacing the Popit valves too

[Art Benham]

Did they just replace the impeller or did they install a waterpump kit in it? the housing gets distorted and a new impeller isn't always the right answer. there should have been signs of possible blockages, some guys just cram an impeller in it and send it !

[Ryno23]

They said they replaced the water pump and thermostat and told me it was fixed.

[Skippers Trophy 01]

Take it back to them, a reputable shop will make good on it if they missed or F****d something up.

[Knotlost]

You can fix everything and fix it right, then slide the lower to the upper and lip over the soft pipe, you will get flow, that works at low speed, but will cook your motor at high speeds.  You can find the GPM of your motor and rpm that it should be sending to the motor on the internet, with a cold motor do the check and see if its putting the right amount of water in the bucket.

[Xxx]

I would put my bet on either the thermostat housing is clogged or the exhaust elbow is clogged. I had a nightmare on my hands when I purchased my boat and the overheating problems I over came, this has educated me rather well, it also could be the main motor water pump, but like mentioned above to check that you could do a test to see if she is pulling enough water to that point, next would be the thermostat housing it's self there are ports in there that allow water to be discharged directly into the heads this would be the lower lines, to test this get a 5 gallon bucket and pull a line with it running and see how much water is being discharged and try to measure the amount of each hose, as close as possible, if discharge is less than the other 3 lines time for new stat housing, next would be your riser, I was told to use that acid the use to clean concrete, and dilute it and turn the riser up so you can fill it up with the acid and let set for 2 hours and then clean out with a coat hanger and a air hose keep poking in the holes with the coat hanger and blowing into the different holes till you feel as if you got what you can. I also bought a thermal gun so I can read temp. Very helpful to determine where it's hot, as you need to be careful of the rubber boot between the riser and the exhaust pipe itself, I hope it's just a faulty thermostat, which I don't even run, PAP.

Edited August 12, 2014 by pap

[traveling man]

Take the thermostat out and see what happens.

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[blueghost1]

The boys at Seagers did a great job with the trophy .

[Jetsled]

IR Temp gun on the risers & exhaust manifolds at idle & under power.  too hot to hold hand on them for 3-5 seconds? when was last time they were both replaced?  i bet both the manifold & riser are rusted up & clogged.  take risers off & look.  worst case it is just a 10 dollar gasket that goes between the riser & manifold.

 

hope this helps.

 

jetsled

[devoknevo]

Just a thought, but the brand-new 350 motor in my drag car was running a little hot (200-220) at idle so I changed out the 185 deg. thermostat for a 160 and it runs cool as a cucumber now.

You should still  check for obstructions though.

[lily]

No experience with in board motors but my outboard did the exact same thing this spring. The problem was my water pump was not changed with the impeller and the water jacket was not connected to the bottom of the motor. If there is no water coming out of the motor with it at middle but will flow at high rpm you have a flow problem. Check the pump housing. Put the thermostat in hot water if it opens its not that.

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