Outboard overheating, but not all the time.

[BM]

Hmmm...... Ok Dave..

Can you take it for a run at 4000rpm minimum, preferably at full throttle for say 15 minutes and observe the temp gauge activity?

See, when outboards have temp issues they become very apparent above 4000rpm as this is when the engine is producing big power and therefore big heat.

I'm keen to hear the results of the above test mate. I'm asuming 2000-2800 is sub-planing and is also a time of high load but not high revs. What boat is this on (sorry if you have already mentioned it) and is the cav plate more or less level with the bottom of the hull for a glass boat and the bottom of the extruded keel for an alloy boat? And while we are at it, what is your WOT rpm and what type of prop are you running (no. of blades, pitch)?

Its not much of a surprise that your water galleries were pretty clear. Merc and OMC typically had large water galleries and as such salting up happens a bit but not much. As opposed to Yamaha, which have lots of salting up issues when they get a bit of age on them.

I gather when you refitted the heads you flatted them off first on an emery sheet and fitted new head gaskets?

Cheers

[davez104]

I have never had the heads off BM, it's only the water galleries that I can access elsewhere that I can see are clean.

The motor is on a Haines V17L, it's a 1990 model 135 Merc. It never used to have this problem, or not that I noticed anyway. I only had it out on maybe 3 trips before it started. WOT is about 5200rpm from memory, a bit low I know. Top speed is just over 40 knots with an alloy 19" prop.

If the water is smooth enough that you can hold it above 4000rpm, it doesn't get hot. Below about 15-1800 it doesn't get hot either. It just seems to be when the boat is not quite on the plane yet or when it's just on the plane. This is how it behaved before I parked it in the shed last anyway. Couldn't really test it the other day as it was too rough to keep a good speed. It's a 200km drive to the nearest boat ramp too, which makes it real easy to keep checking things and going for a quick test run

We are really trying hard to pay off all our debts at the moment so we can buy a house, but I am so close to trading it in and financing an optimax or an etec. I know both the missus and the bank manager would scream though.

Dave.

[lunchcutter]

yeah same prob when i first bought my outboard previous owner said not many hours done after last service he said he had a few overheating probs before the service so i buy the motor put it on the back take it out the first time next thing you know overheating alarm was going out yaeh so this happened a few times that day. take here home take out the thermos put in hot water they open fine take it out again same thing happens so the first thing i think is yeah i have just bought a lemon so been told it could be the water galleries in the heat maybe a saly build up of some sought the water flow was fine out the tell tail so dont know take it to the mechanic and he tells me the wrong thermos were put in the motor so i thought yeah yeah yeah never had a prob since travel out 80-90 ks not a prob so what im trying to say is verything may be so simple

[davez104]

Thanks mate,

I've run it both with and without the thermostats in and the problem is still the same. I'm pretty sure it's only going to be something simple that is causing it, thats what is so frustrating. Might take it for a run today or tomorrow and see if it's any better.

Dave.

[davez104]

Just got off the phone with the mobile marine mechanic in Mackay, he seems to know what he's on about and I've heard plenty of good reports about him. I'll take the boat into him on monday and pick it up about two weeks later, hopefully he'll have it sorted by then. He insists that it sounds like a water flow issue although could be head gaskets, will have to wait and see what he comes up with I guess.

Thanks everyone for your help, although I wasn't able to solve this issue by myself this time.

Dave.

[captain rednut]

hi dave the lower water pump housing is my guess
thanks jim

[FNQCairns]

hi dave the lower water pump housing is my guess
thanks jim

Almost without a doubt as best guess and as I initiated up near the top of the thread, one thing for sure once a mechanic gets to it (hope you are not one) it may then once working be 3 different areas and the repair cost will reflect it.

IMO Fully overhaul the pump yourself and the probability is high you may find yourself spending the money saved on a fishing trip or possibly 5.

cheers fnq

[davez104]

Geez, I hope it's not going to be that expensive to replace the water pump!! I did the impellor myself and didn't think it was that big of a job, the whole pump shouldn't be much more.

I'll still get the mechanic to give it a thorough going over as I'm sick of not being able to use the boat and being a 400km round trip to the boat ramp, I've probably spent more money on wasted trips to the ramp than what its going to cost to fix.

Thanks.

Dave.

[FNQCairns]

Dont think it would be as expensive as you think dave to d o the water pump, the expense will come from all of the other bits investigated + the labour to do it.

Possibly to save your self the extra expense and time re-investigate your pump and/or install a full kit through it.

A water pressure gauge can give an indication as it needs both flow and pressure to give a good reading -even at idle on the muffs, this doesn't need a ramp and is a very useful addition to the boat.


cheers fnq

[davez104]

Well, turns out it was just the impellor. He replaced that and put two new thermostats in at my request, and it's as good as gold. The only thing I can put the problem down to after I replaced the impellor, is that the sealing around the water pump chamber had something to do with the continued overheating.

Looking back though, I thought of another possible contributor. I was living in Emerald at the time and after I replaced the impellor I took the boat out to Fairbairn dam and went chasing redclaw, as you do in Emerald The dam was fairly low at thet point and there was a fair amount shallow water traveling happening. Is it possible that the sand, dirt etc chewed out the impellor straight up? The mechanic said it doesn't take much on these old mercs for them to start getting warm, the water pumps are a bit touchy.

Anyway, she's all good now and it cost me about $260, so not too bad I don't think, considering they had to check a few possible causes.

Thanks everyone for your input, I should have taken it to the mech straight up.

Seems it's allways the simple things that bring you undone.

Thanks,
Dave.

[FNQCairns]

Good news Dave, bet you cannot wait to get it on the water again. Not much worse than a boat sitting dry because it's broken.

cheers fnq

[davez104]

Got the call that the boat was ready at 10am on Friday, I was on the water at 5:30 that afternoon. I live about 2 hours away from Mackay and had nothing prepared, so yeah, I was a little keen. Got back to the ramp a bit after lunchtime yesterday

Dave.