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Donzi Dave
04-22-2000, 05:19 PM
O.K. guys - I'm stumped. Boat is off the lift and on the trailer for it's spring shine (wax on - wax off) and servicing. Having an overheating problem. The facts: Mercrusier 5.7L w/ Alpha 1 drive. Lower unit pump fine. New t-stat working fine. By-pass water to exhaust headers flowing well. As engine begins to heat up, t-stat opens but no engine water flow. Culprit would seem to be the engine water pump, but it is not leaking or squealing (the textbook symptoms). Thought I would try to get some advice before tearing all that crap off the front of the engine. Any ideas? Thanks Dave

kingair
04-22-2000, 06:41 PM
Hey Dave
I take it that the problem is at higher RPMs and under load. Before you go through all the trouble of pulling off the circulating pump, check the exhuast manifolds for proper flow. Any blockage in the riser will starve the engine. Also you may check to see if there is equal flow from both exhuast tips at speed ( a person has to be real fast to do this http://206.150.187.82/ubb/smile.giftake the engine hatch off and find a volunteer (sucker) to stand next to the engine and look over the stern, Also using extreme caution...try to see if one exhuast manifold is hotter than the other).

Later
Philip

Donzi Dave
04-22-2000, 07:25 PM
Phillip - Don't know about under load. This has manifested itself sitting on the trailer at warmup throttle. Higher rpm just heats up faster. Already took water temp at exhaust tips. This bypass water is at normal temp and flow is good and equal both sides. However when t-stat opens water flow is supposed to increase. Not happn' - Dave

Richard
04-22-2000, 08:01 PM
Dave,
Double check the water hose between the drive and transom plate. We found one restricting water flow at certain drive and steering angles. (Collapsed) It drove us crazy finding it.

RickR,GroveCity
04-22-2000, 08:05 PM
Dave
Before you mess with anything put her in the water and see what happens.
Sterndrives tend to heat up when connected to a water hose.
I would be surprised if it was the circulation pump unless it is an automotive part.
A good way to check flow and make sure the seawater pump is not sucking air is to attach a clear hose inline on the seawater intake hose. Check with the boat in the water.

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RickR mailto:riggerb@aol.comriggerb@aol.com</A>

FonziDonzi
04-23-2000, 01:27 AM
Hey Dave,
What year is your boat??? Here's 1 test i would perform on the waterpump just to double check and be sure its not bad...loosen the hose connected to it, have someone start the boat for you, and see if you are pushing water. Hope it works out for ya.

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78 Donzi X18
350 chevy
"Suckin gas & haulin ass"

kingair
04-23-2000, 12:17 PM
I also agree with Rick... My Volvo will not run on muffs.
Later
Philip

AVickers
04-24-2000, 11:58 AM
Mine runs fine on the muff -- no overheating -- but I plug the hole in the bottom of the foot.

Be sure that the water pump on the engine (the circulating pump) isn't an automotive unit. The pumps don't drain completely when you drain everything else and I've heard of the impeller rotting off of these so the point that they don't move any water...

GeneD
04-24-2000, 12:28 PM
Here you go, more fuel for the overheating problem!!!!
I was having a horrible time trying to figure out what in the world my overheating problem was.
Same motor and drive as you got.
One day, I got the bright idea to do exacly what you are doing now. But I still couldn't figure it out.
Finally, in desperation, I pulled off the circulating pump. Stainless steel backing plate like it should have. I was reluctant to do so, but I pulled off the plate. Low and behold there were no fins left on the shaft! They were all rusted off. An auto pump! But the maniac had the forethought to replace the plate.
Now, I wasn't OVERHEATING, just a bit warmer than I cared for, maybe around 175 plus. And under load, high RPM's, the motor would get hot. Remember, us raw water cooled guys can't run a high thermostat, I run a 160.
I was getting water into the motor, no doubting that. But the water didn't seem to want to leave under any kind of pressure.
My next step in your boat would be to remove the themostat housing and check for rust blockage. Remove all plugs and hoses and check for flow.
The circulating pump is relatively easy to remove and once off, just as easy to replace. A standard marine type pump should be around $150 give or take depending on your area.
Good luck.

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GeneD
007
Melbourne, Florida

[This message has been edited by GeneD (edited 04-24-2000).]

kevin
04-25-2000, 10:07 AM
GENE, WHY DO YOU SUGGEST A 160 T STAT, WHAT HAPPENS IF YOU RUN A 190?

AVickers
04-25-2000, 11:15 AM
The water inside the engine is a heat-transferring medium. It takes heat generated inside the engine and transfers it to the lake. In all cases, you want this water to remain in a liquid state because that's the state in which it transfers heat the best.

Thermostats begin to open at their specified temperature and are fully open at about 25 degrees above that. Since raw water systems aren't pressurized, they generally begin to boil at around 212 degrees -- lower at higher altitudes. However, there are some places inside the engine where, because of the movement of the water around them and the resulting lower pressure at that specific location, where boiling occurs at even lower temperatures -- sometimes well below 212 degrees. (Prop Cavitation is a similar phenomenon except that the water is boiling at something like 70 to 100 degrees... Very low pressures allow water to boil at very low temperatures -- Boyle's Law. Cavitation is not the same as getting air around the prop.)

Anyway, once the water begins to boil, it's temperature-exchanging characteristics begin to change and high-temperature steam pockets can occur. (Water changing from liquid to steam is very good at stabilizing temperature at the boiling point, but that's generally too hot for safe operation of the engine. Besides, we're trying for water-cooled engines, not steam-cooled...) Once the water has all turned to steam, it no longer stabilizes -- it just gets hotter and hotter (aka super-heated steam). In no circumstance to you want the water to boil inside the engine!

Given this, the absolute hotest thermostat you could run and not have water boiling in places inside your motor would be the 180-degree unit. But, given the nooks and crannies inside the engine where flowing water can make for low pressure areas and just to be on the safe side, a lot of guys will run 160-degree units. (An area where low pressure would always occur in a running engine is around the vanes of the water pump -- a steam pocket here would prevent the pump from moving any water at all. Maybe that's what's going on w/ DonziDave's boat...)

In salt-water, stuff begins to precipitate out even below the boiling point, so 140-degree thermostats are recommended in these applications, if for nothing else, to keep solidified crud out of the water passages.

Heat exchangers allow hotter thermostats in the engine ('cause you can pressurize them), but they cook a look of junk out in the exchanger tubes and need to be rodded/brushed out regularly.

RickR,GroveCity
04-25-2000, 12:41 PM
That gets us to the oil temp
I am a firm believer in an oil temp gauge and oil coolers.
On my 420 HP 454 the water never varies more than 5 degrees but the oil will go from 145 to 260 (I have an oil cooler).
Your oil needs to get over 212 to boil off moisture but should not exceed 260.
I always let my oil get over 160 before WOT and cool down below 200 before shutting the engine down.
BTW Napa has marine thermostats available down to 140 degrees.

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RickR mailto:riggerb@aol.comriggerb@aol.com</A>

Donzi Dave
04-25-2000, 08:58 PM
Hey Guys! Thanks for all the great feedback.
Some more info to consider: Boat is '86 18 2+3 with the original power plant (5.7 w/ Alpha I). Engine circulation pump is original (never been removed). Fresh water boat w/ raw water intake. T-stat is 143 deg. type (new).
Removed, cleaned, and inspected t-stat housing, hoses, etc. When working, normal engine temp runs around 160 deg. Always has had usual temp increase when coming off a hard WOT run down to putt (up to 190 deg for about 20 seconds, then back to normal). Engine has about 750 hours but runs perfect with no oil consumption, etc.
Before I tear into the circulation pump, I think I will take earlier advice and water test after I finish wax on - wax off.
Keep the suggestions coming...Thanks, Dave

Christian
04-25-2000, 09:26 PM
I have the same year boat and had the same prob! here it is

do the water pump bit since its 700+ hrs BUT:
on the stern there is a h20 hook-up. RIP IT OUT these things are junk when you run in salt water areas. Mine was toast and wouldn't allow water to flow well at all causing overheat probs, infact thats why i got the boat, b/c no1 knew how to fix it. It seems unique i know, but take it from the pros at RoseBudRacingCorp. All it is, is just a small piece of plastic with a spring inside and the spring gets shot and won't circulate water through the entire motor, yes you may get water out the pipes but it still gets hot. Now the boat runs as cool as it looks
Good luck i am sure this will help
christian
RoseBudRacing

Donzi Dave
04-25-2000, 10:18 PM
Christian - Good suggestion - but way ahead of you. I removed that in-line "T" flush connector back in '87 for the same reason as you. Dave

GeneD
04-27-2000, 07:02 AM
The reason I run a 160 thermostat is that the salt in salt water crystalizes at 180(?) degrees. In a restriced flow (thermostat) raw water cooled system, it is important to keep the temp down below that number. If not, the salt begins to build up.
This is a long term thing and not to be confused with any immediate problems.
Did I say that right?
Anyway, any higher and you run the risk of early engine failure (500 hrs?) due from blown out cast iron water jackets.
Another reason to flush.
Still don't explain why the new motors with raw water cooling and fuel injection are running 180's. But hey, they must have a reason.
I just know about my little carburated area in the Mercruiser world.

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GeneD
007
Melbourne, Florida

Donzi Dave
04-30-2000, 07:19 PM
CURED!! Why is it always the last place you look? Found a delaminated piece of the inside of the raw water hose to the engine which had folded down blocking about 50% of of the water flow. Replaced it - lots of water - rock and roll. Thanks for all the great advice. Dave

GeneD
05-05-2000, 09:34 AM
Geez, and not one of us had the forethought to check that.
But...I do remember someone saying that you should check the flow!!!!!
Good job.
Mechanic of the day!

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GeneD
007
Melbourne, Florida