5.0 Alpha Gen II overheating at low speed

[Blake05]

I?ve got a 94 20? Searay BR with 5.0 Alpha Gen II with a couple problems. Started to heat up at low speed this year, cools nicely at plane. Pulled it and put an impeller in (old one looked fine) and 140TStat. Housing not plugged, everything else looked OK. On muffs or large bucket of H20, it still gets warm. Gauge says over 200F and IR confirms about 170 at Tstat and 200 at risers. With motor off, muffs don?t push any water up thru inlet to PS cooler but water hose connected in reverse at inlet line at PS cooler does push water out lower unit?????? With engine running on muffs, water is available at PS cooler. First off, should water be able to flow from muffs thru inlet to engine with motor off? I don?t see why not. Especially since it flows in reverse with engine off. I confirmed no flow at transom fitting on muffs with engine off too. I also don?t see water coming out of the prop exhaust on muffs, engine running. Second, could rust or scale clog the engine, water pump, etc. and cause this? I used some rust cleaner (alkaline then acid) for a motor flush and got some rust out of the exhaust water but that didn?t help. Am I just spinning my wheels by trying to do this on land with muffs or big ole bucket of water? Also, my PS is not working, it kicks in when I turn wheel in a quick movement but only for an instance. Any help is appreciated.

 

[Bondo]

Re: 5.0 Alpha Gen II overheating at low speed

I confirmed no flow at transom fitting on muffs with engine off too.

Ayuh,... The Impeller pushes the water,... Without it turning, the muffs will Not move water to the motor...

I also don?t see water coming out of the prop exhaust on muffs, engine running. Second, could rust or scale clog the engine, and 200 at risers.

If the impeller is moving water Into the motor,...
My guess is, the Risers are Plugged....
Water has to be able to get Out of the system, just like it has to get In...

Also, my PS is not working, it kicks in when I turn wheel in a quick movement but only for an instance.

That sounds like the Actuator is Corroded...
Is this a Saltwater boat,..?? Sure sounds like it...

 

[Bt Doctur]

Re: 5.0 Alpha Gen II overheating at low speed

When were the risers replaced?

 

[Blake05]

Re: 5.0 Alpha Gen II overheating at low speed

Ayuh,... The Impeller pushes the water,... Without it turning, the muffs will Not move water to the motor...

Thanks for the response, I'll buy that, but how is it that I can push water in reverse (with a hose connected to transom fitting from inside) out of the lower unit with a static impeller?

If the impeller is moving water Into the motor,...
My guess is, the Risers are Plugged....
Water has to be able to get Out of the system, just like it has to get In...

Does low or no flow out of the prop exhaust support this?
On muffs and running, Water exists from behind bellhousing but not through the prop. Is this normal? I wish I had an exhaust schematic.

That sounds like the Actuator is Corroded...
Is this a Saltwater boat,..?? Sure sounds like it...

Freshwater. the spool slides as the steering is turned but I don't know if it moves enough (I can watch it) and if the actuator was corroded I don't feel I'd be able to manually steer very well, but it does. I can feel the PS kick in just briefly if I quick steer L and R but a noram steer is all manual. I'll chk the pressures, flow is good.

 

[Blake05]

Re: 5.0 Alpha Gen II overheating at low speed

When were the risers replaced?

The risers have never been replaced. hmmm

 

[Blake05]

Re: 5.0 Alpha Gen II overheating at low speed

When were the risers replaced?

Took off risers, all clear, look good.

 

[scutly]

Re: 5.0 Alpha Gen II overheating at low speed

Started to heat up at low speed this year, cools nicely at plane. Pulled it and put an impeller in (old one looked fine) and 140TStat.

did you replace the whole pump kit or just the impeller? i had same problem with hi temp at slow speeds and replaced the whole kit to be sure and shes fine now. my impeller looked good but when i removed it, it was not flexible anymore and permanently "curled"

 

[intrepidvoyager]

Re: 5.0 Alpha Gen II overheating at low speed

Go for a spin..... get up to thermo opening temp ......Check if you can squeeze the hoses going from thermo housing to manifolds/risers ...if they are hard at 2000 RPM you have a blockage in the system past the thermo ...... if you can squeeze them with your hand you have a thermo,hoses,water pump issue/debris in the raw water line.

 

[intrepidvoyager]

Re: 5.0 Alpha Gen II overheating at low speed

re my previous post ......past the thermo means manifold/riser/Y exhaust tube as in old flapper stuck in the tube ...

So you'll know how your cooling system should work here is a write-up on a 350 CID Alpha ...... most small block raw water pumps pump around 20 gpm,
we have a 22 gpm in our big block Rinker ....at 65 mph you can put your hand on the riser !

For example the circulating pump on a standard small V8 GM based engine will flow approximately 50 gpm through the engine. The typical raw water supply pump is capable of flowing about 18 - 20 gpm depending on the gear ratio and restriction the system experiences. A standard 300 Hp small V8 engine dissipates approximately 300,000 Btu/Hr of heat into the coolant. To maintain a thermostat temperature of 160 degree F at wide open throttle this engine would need a pump to flow about 8 gallons per minute (GPM) of 70 degree F water into the system to maintain this engine temperature. Since the Alpha raw water pump can flow 18-20 GPM there is significant bypass (excess) water supplied, which therefore has to be dis-charged somewhere.

In a cold manifold system the warm water that flows through the thermostat, as well as this excess bypass water are joined together in the thermostat before exiting and being introduced into the bottom of the exhaust manifold. The fact that your are mixing together a lesser amount of 160 degree F engine water (8 GPM) with 10+ GPM of cold lake water allows the aggregate coolant temperature in the manifold to fall below the 110 degree F threshold needed to prevent the accumulation of condensation in the exhaust system.

 

[Blake05]

Re: 5.0 Alpha Gen II overheating at low speed

Thanks for the write, my take home on that is I shld have plenty of water flowing in but don't know how much is flowing out. Gonna be hard to chk those hoses as you suggest, they are thick walled ~1in dia. I'll run it like you say and try to evaluate. Any thoughts on the steering?

 

[intrepidvoyager]

Re: 5.0 Alpha Gen II overheating at low speed

This is what it should look like ...notice after system fills with water ....water NOT STEAM ...flows out of relief ports on either side ..and the prop exhaust.


http://www.youtube.com/watch?v=holZI181KzM


OK ...at this point its best not to assume anything ...... you may have good gpm flow from your raw water pump but you may not have ideal..... re the squeeze hose test ... this is only to see if you have a pressure build up in the hoses going to the manifolds which indicates a blockage in the manifolds or risers or debris in the Y exhaust tube... see how much you can squeeze the hoses when the engine is turned off .....even if you have to use plyers ...you need only squeeze the hose by 1/4 of an inch cold ......you will able to tell right away if you have a blockage as at 2000 RPM as the hoses will be very hard. If they are hard on muffs go to (INSP)

WARNING ..... do not let your risers get over 200 on your IR thermo or you can start to burn the rubber on the riser to Y tube!

WARNING ...do not attempt to check risers by hooking up a garden hose to the riser hose as you risk getting water in the engine !!!

So if the hoses are hard you have good pressure from the raw water pump BUT maybe not up to spec .....we'll get to that in a moment .

(INSP) So if you find the hoses are hard you got a blockage problem...... first pull the hoses and check for debris at the hose to manifold fitting ..... then pull the risers and check the water jackets for blockage ....check that the gaskets are properly installed and that you have the right gaskets ...... go fishing down the Y tube with a coat hanger wire and mirror and light and make sure there is no debris in the Y tube like old broken shutter ...Get hold of a new riser and compare to yours ...... if you have corrosion build up on the water jacket walls this is enough to block proper coolant flow ..... if the risers have been running hot due to poor impellor even in fresh water they will rapidly corrode .... any pro merc mechanic can tell you or maybe they are so bad its evident that they should be replaced. If there is any scale in the exahust tube itself they should be replaced! the inside of the riser should look like the inside of the tail pipe on your car/truck ...carbon , thats all !!

without a flow bench its very hard to test manifolds ...if the risers are OK then the problem IS the manifolds ....... if the risers are dodgy ..replace them.

OK ...about manifolds ....... basically they have an average life expetancy
of 6 to 8 years .....just had a friend ruin his 3.0 engine with 7 year old manifold ...... up to you

lets say for the sake of "how to test your GPM flow" that you fix above problem and elliminate the blockage .....

You got a bin to stick the leg in ....excellent ...... so mark down from the top of the bin 10 gallons of water ..... remove any hose refilling the bin and start the engine at zero seconds ........ watch the level of the water in the bin ...after 30 seconds your raw water pump should have picked up around 9 gallons. If not you have a pump issue as I gather you have backwashed any debris out of the cooler line. KEEP IN MIND this test is useless until you have free flowing manifolds/risers.

Based on the fact you have checked the impellor odds are risers/manifolds are the issue .....GOOD LUCK

 

[intrepidvoyager]

Re: 5.0 Alpha Gen II overheating at low speed

OK ....so if your hoses to manifold are not rock hard at 2000 RPM , boat moving , then you probably have an impellor issue that is causing overheating at low speed RPMs ..... like was said before .... impellor can look good but is fin soft so pump does not function properly at low RPMs ..... get a new impellor.

re STEERING ....appears you got fluid blowby ..... when you turn fast the fluid does not have enough time to leak past the steering cylinder pistons . turn slow it does ........ apart from servicing the unit you can try draining out all the old fluid , including what's in the cooler, resevoir, etc and replacing ..... old fluid may have been viscosity compromized .

 

[Blake05]

Re: 5.0 Alpha Gen II overheating at low speed

Intrepid, thanks for your input. I?ve got the "newer style" control valve, says it's not serviceable like the older one???

I like your idea of fluid change out, I kinda thought it could be a "hydraulic" issue. When you say fluid blow by, do you mean the fluid is sneaking past the spool valve to other ports when I turn fast? Hmmm...

I disconnected the actuator to the stern and manually pushed the control valve from neutral to left and right. Actuator moves with full power both ways! It seems my spool valve is just not traveling far enough with steering cable force only. Tried to lube it up (spool valve) but not much better, maybe a bit though. This leads me to believe the spool valve is sticking. At this point it seems to draw a little pressure when I turn slow (indicating the actuator sees some fluid pressure) and I wonder if I just don?t know the steering system like I thought I did.

It?s not too terrible to drive w/o power steering or maybe I do have the system working but I expect too much. It?s just that I do feel it kick in when I turn hard and the steering is smooth and effortless for an instance. Is that the way they are designed?

I wish I knew if there was a pilot portion and a full bore portion to the spool valve. I wish I knew a steering expert.

The fluid changeout may be the trick, I thought that maybe my spool valve was seeing too much drag indicating lack of good lube so I thought maybe a friction modifier. But everyone says tranny fluid or P/S fluid, it doesn?t matter, so I haven?t given it much thought. Does one tranny fluid have better props than another i.e., mobil 1 synthetic, Dextron II, III, Type F or P/S fluid, how bout some thicker synthetic motor oil?

Has anyone taken apart and cleaned a ?newer? control valve spool? Why do they say it is not serviceable? 94 20? Searay BR with 5.0 Alpha Gen II

 

[intrepidvoyager]

Re: 5.0 Alpha Gen II overheating at low speed

OK .....open this up ......could not find a schematic url for boat steering but the concept is the same

http://www.2carpros.com/forum/automotive_pictures/12900_steeringpowerrack_1.jpg

see the piston ...ok ...so what I mean by blow by is probably better described as leak by .....quick wheel movements do not allow time for fluid to leak by the piston, but slow ones will ...

never pulled one apart so can't help there.

re type of fluid ...... use GM type clear PS fluid ....... same as original Mercruiser ..... have heard but not pos that some ATFs can damage seals over time.

 

[intrepidvoyager]

Re: 5.0 Alpha Gen II overheating at low speed

oops ...just remembered due to a new PS issue over here in Hawaii.....ya ...had a sit with my wife's turbo saab long ago ......anyway it's got a Saginaw rack but Saab said DO NOT USE ATF ....you can probably find stuff on the web about this ...
Also remebered PRESTONE makes a clear PS fluid with some kind of stop leak additive .....maybe worth a try.