5.0 Mercruiser sick

[Rolf Latham]

Hi All

First post in desperation

I have a Bayliner 2355 Ciera, fitted with the Original 5.0 Carb 230 hp engine, raw water cooled, running Alpha 1 drive and a 17 prop

Purchased the boat about 7 mths ago, 1996 model in good condition overall.

Just previous to purchase fitted with new manifolds and risers, passed its pre purchase inspection test all fine, good compression, easy start, great running etc .

About 30 hrs use later cracked a head, ok no big deal, tow it home, empty the engine, fit a new head, check out cooling etc all good. Running great again.

5 hrs later ..................crack the other bank's head.

Both Heads had shown signs of valve seat recession and a bit of corrosion, I assume from the old manifolds which may have leaked a little.

Replace the second head with a new one, while out of the water, do the sterndrive impeller, leg service, do the thermostat and general cooling check etc .

Ruuning fine, stronger than ever ..........and very happy .............for an hours running time


Suddenly.....low power, will just get on the plane, though revving ok, with occasional misfire, one manifold running cool to touch, other side noticeabily MUCH hotter.

In addition, temp guage is showing slow flucuations of from 100 to 175 degrees on plane...................

Pulled leg and cooling system to bits, replaced missing shutters, no obvious blockages, compression good, no water in the oil etc

Timing is ok, new leads, new plugs, both barrels on the carby ok, fuel is fresh.

Starts easy, runs at 2000 rpm clean and ok temp, as soon as asked to load up she doesnt want to move to much............

My mechanic and I are both at wits end.

Im close to spending the money on a 4.3 MPI re power, and tossing the old engine out as a boat anchor............BUT just before making that big commitment I thought, hey ask someone else

Ideas please ?

ta
rolf

 

[Don S]

Re: 5.0 Mercruiser sick

IF you put in a new engine, you would probably have the same problem.

Try this before you spend a bunch of money for no reason.
http://forums.iboats.com/showthread.php?t=167561

 

[JustJason]

Re: 5.0 Mercruiser sick

runnin leanie weenie.....

that won't explain the temp fluctuations like you described though....
that's more likely a different problem.

make sure there's no restrictions in the fuel

check the gauge, sender and wiring between the 2 for the temp...

 

[MikDee]

Re: 5.0 Mercruiser sick

That boat sounds Overpropped! I had a 24' Searay Cuddy with a bigger 5.7 350/260 hp, always light loaded, no bottom paint, with thru hull exhausts, and a 14X17" pitch Aluminum prop, and I was slightly overpropped, fully trimmed out at 4600rpm, & 40mph. If you have a Stainless prop on there, it's definitely overpropped! They load up an engine more then an Aluminum prop of the same size. There's only so much a small valve, small piston, 5.0 305/230hp can do! No wonder you're engine keeps breaking down. Granted my boat might have been a bit heavier then yours, but I also had a tried, & true, more powerful 5.7/350. You need to fix your engine, make it strong again, & drop some pitch from that prop, your rpm range needs to be reaching at least 4200-4600 rpm WOT.

 

[Rolf Latham]

Re: 5.0 Mercruiser sick

Thanks

Will run the fuel checks.............certainly could be an easy fix for the power, and will go to a 15 inch prop and I willbe back.

She used to comfy sit on 21 knots doing 3300 to 3400 rpm, would never get over 4000 rpm though even at full throttle with no only one person on board, so that prop is likely a little long using your max rpm figures

ta
rolf

 

[Bondo]

Re: 5.0 Mercruiser sick

replaced missing shutters,

Ayuh,.......

Did you recover,+ remove the Missing Pieces,..??..??

If Not,......
They tend to lay in the exhaust channel,+ cause considerable extra Back Pressure,.......
Which Could cause the Issues you're having......

 

[TilliamWe]

Re: 5.0 Mercruiser sick

would never get over 4000 rpm though even at full throttle with no only one person on board, so that prop is likely a little long using your max rpm figures

ta
rolf

Ding Ding Ding, we have the source of one of your problems! You need those WOT rpms to be much higher. The valve "recession" you saw was cause by "lugging" your engine. This causes very high combustion chamber temps and warps the valves. Get a new prop and that will go away. Try a 15. (on a side note, I looked at a 2355 for sale with a 5.0 and there were 4 different props on board, obviously searching for one that would work!)
Not sure why your manifolds are different temps, but fixing that is critical too. DonS and Bondo are pointing you in the right direction.
After reading my post, you actually need to fix any "power" issues and the cooling problem first. Then tackle the prop.

 

[JustJason]

Re: 5.0 Mercruiser sick

its common and okay for the exhaust manifolds to run slightly different temps. You'll find that 1 side is usually about 10 degrees hotter than the other. The biggest thing is to get a pyrometer and find out exactly what temps they are running.

 

[MikDee]

Re: 5.0 Mercruiser sick

Thanks

Will run the fuel checks.............certainly could be an easy fix for the power, and will go to a 15 inch prop and I willbe back.

She used to comfy sit on 21 knots doing 3300 to 3400 rpm, would never get over 4000 rpm though even at full throttle with no only one person on board, so that prop is likely a little long using your max rpm figures

ta
rolf

Hence overpropped! Don't assume a 15" pitch prop will work, or fix the original problem, First you need to get your engine issues fixed, then try a 15" pitch prop, take it out, & run it WOT (wide open throttle) check your rpm's if they're not in the upper part of the range I mentioned, with a light load, back off in prop pitch till you reach that rpm at WOT(4600)! because if you load the boat up with people, & gear, you still want to be at least in the lower end of that range at WOT(4200) for your engine to be able to handle the load, and run efficiently.

 

[sarantis]

Re: 5.0 Mercruiser sick

i have exactly the same problem with the difference that the engine got overheated in the hands of somebody else before buying it and without knowing it.I wish Bond-o had sent me this reply as my boat(gm 305 1978-82)had exactly the same symptoms and the only thing i couldn't imagine and also wasn't suggested to check was the Y-pipe exhaust.i am almost sure that the one side is clogged but i thought it was from a destroyed shutter.Now Bond-o put in thoughts as he refers something about "missing pieces".Can anybody tell me what does he mean?

 

[sarantis]

Re: 5.0 Mercruiser sick

Sorry i didn't notice that you ve changed shutters.But if they are close to the risers (high) you maybe your exhaust is clogged at the botom.my shutters are at the botom where the two chanels are conected.But something else that i haven't checked and i consider it possible and as i saw you haven't changed either is the distributor cap (if your engine has).

 

[Bondo]

Re: 5.0 Mercruiser sick

Ayuh,.......

This is what I'm talking about............

 

[sarantis]

Re: 5.0 Mercruiser sick

Is this a destroyed shutter?!!!
Very kind of you ,thanks a lot.

 

[Rolf Latham]

Re: 5.0 Mercruiser sick

Hi All

Time to report back

15 inch prop has done the world of good

Did lots of test work as suggested .


Engine is now back onto full power ........................something so minor ...........but in desperation you try small things ........when the leads were replaced the coil lead didnt want to fit very well, so the old one was re used..........ho hum.

Well, a $ 9.50 part and we are back at cruisjng at a top speed of about 30 knots ( faster than shed ever be able to go before )

Im not out of trouble yet though, maybe Im just imagining things but something doesnt feel right still about the temps.

Invested in a laser thermo thingie and interesting results

The temp guage is showing slow flucuations of from 100 to 175 degrees on plane...................

Under moderate load the top of one riser is as 165, the other is at 100, remembering these are near new and have recently been re checked when we did new heads.

The Egine temp on gauge NEVER goes above 175.

The outlet temps from the Riser hoses ( the ones from the thermo housing are) about 20 degrees different.

i have used the clear hose idea, and one side does produce some air bubbles, but not a huge amount.

We have also reversed the hoses from the stat to the risers, and this means the HOTTER riser is now on the other side. This suggests its not the mans or risers, but something upstream of the stat.

New shutters, no obstructions, new impeller.

Any silver bullets please

PS

it runs really well, so am I paranoid over nothing ?

ta
rolf

 

[flabum]

Re: 5.0 Mercruiser sick

The thermostat housing may be partially plugged. Water will flow in the direction of least resistance. Pull the housing out and give it a good inspection.

 

[Rolf Latham]

Re: 5.0 Mercruiser sick

Thanks

Shes all clear............... and she has a new stat thats tested to work.

Its the "newer" style housing without the ball valves BTW

ta
rolf

 

[JustJason]

Re: 5.0 Mercruiser sick

the top of one riser is as 165, the other is at 100, remembering these are near new

Is it just the risers that are new, or are both manifold and both risers new?

160 and 100 isn't normal. 110 and 100 would be. or 130 and 120. 160 is about the temp when they get replaced. I don't know what Don will say but for me on a freshwater cooled engine 160 is where I draw the line for manifolds.

Run the boat around a bit and measure the temps of the manifolds in 3 places. Front, middle and back.. for both sides. Then measure the Riser in 3 places. Inside, outside, and front (the back is a little hard to get to). Post your temps then. In the meantime remove the drains on the manifolds and see how much rust you get out. May have to poke around with a screwdriver.

 

[Rolf Latham]

Re: 5.0 Mercruiser sick

Hiya Jason

Thanks

New risers and manifolds.

Will do the 3 diff temps checks on the weekend.. .............if I survive crawling around in the engine bay under full steam

ta
rolf

 

[mcleaves]

Re: 5.0 Mercruiser sick

OK, I'll throw it out there... What brand manifolds and gasket kits are we talking? There have been a number of threads about gaskets not fitting correctly from a certain mfgr. You need to be sure the water jackets are not getting blocked.

At the very least I'd pull the risers and make sure they are clear. You've been digging around in the cooling system and who knows what may have gone downstream.

M

 

[newport dave]

Re: 5.0 Mercruiser sick

We have also reversed the hoses from the stat to the risers, and this means the HOTTER riser is now on the other side. This suggests its not the mans or risers, but something upstream of the stat.

If this is true than it's either a wrong or bad thermostat housing, or more likely low seawater pump pressure. As others have said, it's not uncommon for one side to run a little warmer than the other, and when there is low pump pressure it becomes more pronounced.

On a warm manifold system 165-175 for the manifolds is normal, but the risers should run around 110-120.

You said it had a new impellor, but there may still be some problem, maybe a bad housing or a vacuum leak on the intake side of the pump.