Dumb question...why are there engine water pumps?

[F14CRAZY]

Yes, I know, there aren't dumb questions, but this one might be...

Last season the water pump/alternator belt broke on my OMC 3.0L...I could only tell because the voltage gauge was a little lower and I knew the belt was on its last legs. But heck, the engine temp didn't seem to rise at all and even the battery held up fine, and we ran it for like an hour. I've replaced the belt since then but was wondering, if the impeller in the sterndrive can cool the motor, what's the engine mounted pump for? Aren't you screwed if the impeller fails regardless if the engine's pump is operating?

 

[mthieme]

Re: Dumb question...why are there engine water pumps?

Interesting - never thought about it.
However, I'm fresh water cooled, so my system is closed like your auto.
busting a belt would be an issue for me...darn, yet another item to replace come spring. (current belt is original - 1989)

 

[Big Boat Bay Buster]

Re: Dumb question...why are there engine water pumps?

Holy cow man, consider yourself lucky. It should be obvious to you that the engine pump will circulate water throughout the engine.The sterndrive pump gets water to the thermostat houseing on top of the engine. From there it goes PAST the engine and out the exhaust manifolds/Risers. I don't see how it would circulate through the engine When the thermostat opens, the engine water mixes with the raw water and re-enters the motor,at least thats my understanding. With this said, i don't see how your engine didn't overheat. I bet you had some hot spots.
The real question is why didn't you change the belt when you knew it was bad. AND, why did you keep running the engine when it broke? I hope you just idled it and made a b-line for shore. Are you telling us the whole story, something smells fishy!!
Chris

 

[F14CRAZY]

Re: Dumb question...why are there engine water pumps?

Don't know how it stayed cool either, but it did. Temp gauge stayed on 180F, where it normally runs at.

This is what went down...I'm fairly new to boats still, and both my dad and I agreed that it looked really worn out...

Went to the dealer and asked for one...out of stock for a few days.

"The thing looks pretty thin, I don't think its going to last much longer"

counterperson: "yea they come that way though...some people try putting automotive type belts on instead but they don't sit in the pulley grooves right."

mmmkay I'll be back for one anyway.

But my buddy and I had been planning on taking it out to Gun Lake for a while so F the belt we're gonna go scout out some boat chicks...

Would I normally skimp on something on the boat? No. By all means skimping on something could mean my life. And, I should have limped it back to the dock or begged for a tow. But given the specific circumstances I came out okay.

So now you know the story

 

[Big Boat Bay Buster]

Re: Dumb question...why are there engine water pumps?

Thanks kid, You just reminded me I'm getting old. I probably would have done the same thing 20 years ago!
I just used automotive belts on my Merc 350. I figured its a "marinized" motor and the belts would work which they did. Mabey someone will chime in on the "do we need marine belts" question
Chris

 

[fishrdan]

Re: Dumb question...why are there engine water pumps?

counterperson: "yea they come that way though...some people try putting automotive type belts on instead but they don't sit in the pulley grooves right."

Now that does sound fishy...

My Mercruiser 3.0 has automotive pulleys; crank, waterpump and alternator. Heck it's just a marinized automotive engine. I had a bent water pump pulley, took it down to the Chevy dealer, they matched up the P/N stamped into the pulley and ordered me one. I wouldn't think the OMC 3.0 would be different for the pulleys/belt.

 

[chiefalen]

Re: Dumb question...why are there engine water pumps?

What is this a stringer drive, with the half moon gear to raise and lower the drive?

Has a big impeller, very large.

It might be the only thing cooling your motor right now. Even with a belt on the motor.

How you ask, seeing there is a water circulation pump on the front of your motor thats belt driven.

Well maybe, just maybe, theres no vanes on the circulation pump, cause no one has ever took it off to look.

And thats why your running at 180, instead of the 160 your supposed to be running at.

Has anyone ever looked at the t-stat to see if it's working?

Might be half closed and stuck that way.

Or maybe the riser is half chocked up with stuff.

Anyway water moves to the engine bye the drive pump pulling water up.

And the circulation pump moves the water around the water jacket of the head and block, pulling the heat away, out the manifold that is hot and out the riser that has a water jacket.

Now here is a little tip and info for you, the marine belt is a little different, and the belt pulls from the sides not the bottom of the v.

And you should have had a spare belt tied around the front mount, when you do go to install the belt, so when the next one snaps you have one already around the mount, and all you would need is a 1/2 flat wrench and a piece of pipe for leverage against the alternator.

Oh yea had to come back for the last question you asked.

Yea your royally messed up if your impeller goes on the drive, and if you ever see the temp go to 190 shut it down and wait till it cools off.

Never let it get past that.

Oh young man, younger people than you, read this forum PLEASE don't use the word you used in the last question.

Good luck and welcome aboard !

 

[TilliamWe]

Re: Dumb question...why are there engine water pumps?

F14, on some high performance engines the engine mounted water pump (circulation pump only) is eliminated. The raw water impeller pump does all the pumping. But Mercruiser and Volvo Penta have decided not to do that on their regular engines.

 

[abj87]

Re: Dumb question...why are there engine water pumps?

Just go to the auto parts store with the belt and they should be able to match it up watch out for the width some are 3/8 and others are 1/2 in wide.

 

[chiefalen]

Re: Dumb question...why are there engine water pumps?

ok the belt is 41 1/2 inchs's long, 29/64 top. Johnson belt #0910343.

Merc quicksilver # 57-64032Q 1

Both will fit. Both have the same top and length.

Now what auto belt is exactly the same?

So i can write it down, save my money also.

 

[a70eliminator]

Re: Dumb question...why are there engine water pumps?

I don't know exacly what the difference is but the alt-w-pump belt on my omc is narrower along with the pullys than any automotive belt I've seen, it's an OEM belt says omc right on it, I have not yet tried to match it up to a semetrical V belt.

I have one of those emergency belts that I took with me on a family vacation, it's a round extruded, strechy piece of heavy tube with a connector works like a chineese finger tourture, you just cut it to size pull it around the pullys and put it together. It looks like it would really work and no need for tools other than a knife to cut the tube to size.

Today we have serpentine belts on our cars, I never had to use the instant belt, If I ever come across another one like it I may consider it for mt boat. If anything it may let someone else (guinea pig) going.

 

[F14CRAZY]

Re: Dumb question...why are there engine water pumps?

Got it. All of it (language included)

Before I put it back in the boat I'll check out the T-stat, or just replace it, and inspect the water pump

 

[JustJason]

Re: Dumb question...why are there engine water pumps?

Every engine setup is a little different (ie 2.3ford, 3.0GM/Merc 4.3, 5.0, 5.7, 6.2, 7.4, 7.5, 8.1 etc etc)
But for the most part... the engine circulating pump really isn't needed. It definitely helps at low rpm when the flow from other water pump is minimal. And if definitely helps if you have a warn impeller where flow is reduced yet again.

 

[chiefalen]

Re: Dumb question...why are there engine water pumps?

Why hasn't others jumped in.

The engine mounted water pump is absolutely needed.

It's the pump that gives you the pressure.

It with the oil combines to help dissipate, the heat that the motor, and cylinders put out.

He is fortunate that the impeller in stringers are over sized way big compared to other impellers.

People over look the part oil plays in carrying away heat in motors.

Thats why oil breaks down,is cause of the heat.

Thats why oil needs to be changed, the heat carrying abilities are compromised when it breaks down.

I know i strayed from the original intent of the question.

However in closing the engine mounted water pump is imperative, in the correct operation of these motors, the way they are designed.

 

[JustJason]

Re: Dumb question...why are there engine water pumps?

It's the pump that gives you the pressure.

Not gonna agree with ya on this one alen. The circulation pump is just that, a circulation pump. It does not in any way generate positive pressure.
An flexible impellar type pump, wether it's in the drive or engine mounted, is a positive pressure pump.

 

[HT32BSX115]

Re: Dumb question...why are there engine water pumps?

Thats why oil breaks down,is cause of the heat.

Thats why oil needs to be changed, the heat carrying abilities are compromised when it breaks down.

I am gonna disagree with this also. Marine engines run VERY cool. Using the above logic you would never have to change the oil.

You have to change the oil because of the increase of contaminants ( combustion products from blowby) and water which produce acids.

The thermodynamic (heat transfer) properties of oil are largely unaffected by using it in an engine. [ Ya see? if we work at it we can turn any thread into an oil thread!!]


TilliamWe is right. There are several racing/high performance engines that have a bypass manifold in place of the circ-pump.....it's very common. They're called Cross-over systems

CP performance is one company that sells Crossover systems for just about every V-8 out there...


Merry Christmas y'all! (can we still say that? )

 

[F14CRAZY]

Re: Dumb question...why are there engine water pumps?

I am gonna disagree with this also. Marine engines run VERY cool. Using the above logic you would never have to change the oil.

You have to change the oil because of the increase of contaminants ( combustion products from blowby) and water which produce acids.

The thermodynamic (heat transfer) properties of oil are largely unaffected by using it in an engine. [ Ya see? if we work at it we can turn any thread into an oil thread!!]


TilliamWe is right. There are several racing/high performance engines that have a bypass manifold in place of the circ-pump.....it's very common. They're called Cross-over systems

CP performance is one company that sells Crossover systems for just about every V-8 out there...


Merry Christmas y'all! (can we still say that? )

Based on my knowledge I would agree that at least my 3.0L runs cool. I mean a 160 degree stat? Automotive engines usually have a 190-195f with the cooling fans turning on at like 215f (GM 3800s)

Regardless, I'll be replacing my stat for good luck and inspecting the water pump, and the impeller in the sterndrive since I have it off anyway

 

[Don S]

Re: Dumb question...why are there engine water pumps?

I've seen inline engines run fine without the engine circulation pump, but never a V engine. That belt goes, and they seem to overheat, maybe not 260? overheat, but it will go up to around 200 and level off.
The circulation pump does just that, makes sure you have water circulating thru the block and head, nothing to do with the manifolds.
Even if they weren't necessary in all cases, many engines are fresh water cooled with a closed cooling system.

 

[chiefalen]

Re: Dumb question...why are there engine water pumps?

Raw water cooled marine engines run cool cause they are using cold water coming in and not recirculating.

The water entering is probably around say 50 degrees, no need for a radiator as on a auto. Also there is no need for the extra heat cause no heat is bleed away for the indoor car heat.

The t-stat is needed to allow the water to heat a little other wise you would always have cold water hitting the water jackets and maybe cracking them.

The Bravo has no impeller in the drive, why cause it's designed differently in conjunction with the motor.

Some volvos have this setup also. But i don't know these new volvos well, i stay away from volvo posts.

But i am enjoying this post more than most, thats what is great about this forum, we are free to discuss different opinions in a gentleman manner.

 

[F14CRAZY]

Re: Dumb question...why are there engine water pumps?

I would have been done for if I had a closed loop system