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Old 09-12-2009, 18:24   #16
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According to Jabsco Engine Cooling > Support Centre > Jabsco - ITT you need about 15 gpm per 100 hp for heat exchanger cooled engines, so your 4.5 gpm should be OK.
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Old 09-12-2009, 18:37   #17
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Change the impeller because this is a butt simple thing to change and you should be carrying spares anyway. Then the pump should be working as designed and the flow will be the flow. If the engine is assembled to spec - i.e. right pump and the right impeller - you get what you get.
Actually, I've been told recently that even if with a new impeller, it's quite possible for a water pump">raw water pump to pump less efficiently over time. The engine is over 20 years old.

The boat formerly had a 22HP engine; current one is 28HP, and I know of the same boat with this same model of engine. I bought the engine rebuilt, and have a description of the parts replaced on it, or rebuilt, but it's not clear if the raw water pump was replaced (rings, valves, bearings, lots of stuff was done in the rebuild). I mention this only b/c speaking to a marine pump shop today, I learned that raw water pumps do eventually wear out and pump less efficiently, especially after many years, the housings wear down, impeller vanes make less contact, flow is less. Anyway, I'm just making educated guesses, really!

I'm not sure why you say that comparing similarly sized engines for raw water flow specs isn't necessarily useful...I mean, I can't imagine other 27-29 HP engines with similar max. RPMs could be that different? Not knowing how much water is supposed to be coming out of my exhaust, it seems like one needs something to compare it to, no? Just to start with. I mean, a very similar engine to mine (27 HP, 3400 max. RPM) moves nearly 50% more sea water per minute at max...seems somewhat remarkable to me.

But, again, I need to go back to the basics before going deeper into this --b/c the overheating occurs under load, not at the dock in throttle only! A too-tight shaft packing gland...hadn't considered that.
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Old 09-12-2009, 18:39   #18
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Originally Posted by donradcliffe View Post
According to Jabsco Engine Cooling > Support Centre > Jabsco - ITT you need about 15 gpm per 100 hp for heat exchanger cooled engines, so your 4.5 gpm should be OK.
Very interesting --thanks for this information.

I'm still puzzled why similarly sized engines that I have specs for (that I mentioned earlier) move quite a bit more water than mine. Anyway, the Jabsco info is certainly informative...thanks for that!
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Old 09-12-2009, 19:01   #19
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Jud...when you check the impeller...check to see if the inside of the cover plate is worn...it will get a groove in it over time...and be less efficient.....I don't think this is your problem but...it's not a bad part to replace if worn...to maintain optimum performance.
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Old 09-12-2009, 19:13   #20
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Measure your water flow from the exhaust for two minutes into a bucket

Measure your water flow to the exhaust elbow for two minutes.

May tell you if you have an obstructed elbow.

Do you have a hot water heater plumbed into the system?
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Old 09-12-2009, 19:14   #21
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Originally Posted by Jud View Post

I'm not sure why you say that comparing similarly sized engines for raw water flow specs isn't necessarily useful...I mean, I can't imagine other 27-29 HP engines with similar max. RPMs could be that different? Not knowing how much water is supposed to be coming out of my exhaust, it seems like one needs something to compare it to, no? Just to start with. I mean, a very similar engine to mine (27 HP, 3400 max. RPM) moves nearly 50% more sea water per minute at max...seems somewhat remarkable to me.

That comment is because you have to put the water flow in the context of the entire heat exchange process. Your engine could be designed for lower flow and larger heat exchanger contact area. Another engine could have less contact area (smaller heat ex) and higher flow. Dwell time - how long the cool water exchanges with the hot water is a function of back pressure and heat exchanger flow capacity.

The point being that comparing different makes could be misleading.

This is an unregulated system and depends on system design for efficiency.

Not saying this is the issue but I put a 327 chevy in a toyota pick up in my youth. It overheated. I put a bigger radiator and high flow water pump and it still overheated. I eventually went to the radiator guy and he said the water wasn't staying in the radiator long enough to cool down. We put a smaller radiator and a bigger fan on and fixed it.

As a science project you could measure the temperature of the raw water out the exhaust. If the water is "cool" then the exchange process isn't working right. I would have no clue what the spec should be. When my boat gets "fouled" or overworks the raw water gets really hot - until it becomes white steam out the exhaust - this indicates to me the exchange process is "at capacity."

When you are overloading does the exhaust water turn to steam? Is it almost "boiling."

You state that you re-propped and my grandma always told me, "Dan, go back to the last thing you messed up and start from there..."

Regardless what the prop guys say, I personally would be propped so that at WOT I can readily reach governing speed. This allows for fouling and other issues to propogate and I still have plenty of mechanical advantage in the propulsion department.

I do agree that the entire pump housing could be worn but I doubt normal wear could result in half flow.

Don't rule out the pump as I mentioned the sheared key possibility. Remove the impeller and look for wear on the housing and a sheared key.

When troubleshooting - especially over the internet - we never have all the information. So the responses are part troubelshooting advice, part guess and part investigation. If I were "on-site" I would be after this kind of information:

Engine make/model
Prop make/model spec
Pump P/N
Heat Exchanger P/N
Boat displacement/LOA
Recent history - prop change type stuff, bottom paint, prop condition, (stuff you are providing so far)

Then I would inspect the components. The most important being the exhaust system, inlet system, heat exchanger condition and water pump condition.

At this point we don't know the condition of the pump itself and it's a 1 hour job to have a look.
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Old 09-12-2009, 19:19   #22
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Before you replace or rebuild pump check for partially restricted intake, mussels in the thruhull, kinked or collapsed hose. Also look at HXchanger for blockages and don't forget the nipple at injection to exhaust.

My 3 cyl Volvo (2030) gets about 7 gpm at 3000 and 3 gpm at 1000.
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Old 09-12-2009, 20:35   #23
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Well Gang,
It has been a long day....winterizing the late-bloomers/die-hards.
As soon as I come in the door from the boats, this is the first page I go to.

With regards to the water flow issue, here is a link that will tell you what output you should get from your pump at what RPM.

http://www.johnson-pump.com/JPMarine...010_US_web.pdf

Aren't you glad you don't have to pay for this info.......you could always send a small contribution to.........
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Old 10-12-2009, 10:55   #24
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Jud...when you check the impeller...check to see if the inside of the cover plate is worn...it will get a groove in it over time...and be less efficient.....I don't think this is your problem but...it's not a bad part to replace if worn...to maintain optimum performance.
In fact, I did have a look at my impeller pump cover inside (it's a Speedseal --www.speedseal.com). I replaced the stock Volvo cover some time ago after two of the heads of the tiny screws sheared off, and the Speedseals supposedly have a good reputation, and large easy to grasp s.s. knurled thumb screws).

Anyway --I did notice a groove in the inside of the cover. Of course, I stupidly didn't save the stock impeller cover, so I can't compare flow with the "right" cover on it! Duh! The stock impeller pump cover had a paper gasket inside. The Speedseal has a thin groove machined in it, into which a very thin rubber o-ring sits. Who knows, maybe the seal is bad and water is pushing past the pump...another thing to look into.
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Old 10-12-2009, 11:10   #25
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That comment is because you have to put the water flow in the context of the entire heat exchange process. [Etc.]
Thanks --makes total sense...thanks for the very informative explanation. I can see that there's definitely a bit more to raw water flow measuring than just comparing similarly sized engines!
Quote:
Originally Posted by Ex-Calif View Post
You state that you re-propped and my grandma always told me, "Dan, go back to the last thing you messed up and start from there..."

Regardless what the prop guys say, I personally would be propped so that at WOT I can readily reach governing speed. This allows for fouling and other issues to propogate and I still have plenty of mechanical advantage in the propulsion department.
Yes, I agree...the re-propping issue has been an ongoing suspicion of mine. We may be still be somewhat over-propped, and that could be causing the overheating (which happens while in gear underway). Unfortunately, this is harder to test, not having a somewhat smaller prop (slightly less pitch, probably) to put on that would allow us to reach max. RPMs at WOT in gear, so that I could compare that prop with the current prop. But, yeah, you're right --it should remain on my list of possibilities until I'm satisfied it's not the issue. [/QUOTE]

Quote:
Originally Posted by Ex-Calif View Post
When troubleshooting - especially over the internet - we never have all the information. So the responses are part troubelshooting advice, part guess and part investigation. If I were "on-site" I would be after this kind of information:
Thanks a lot of your insights and advice --it's a huge help. I see what you mean --it is hard to troubleshoot over the internet, since I've probably forgotten to add some salient info on the boat/set up/recent bottom paint, etc., so it's hard to troubleshoot completely without being on site, of course. In sum, I'm going to go over everything --including re-testing gauge vs. actual engine temp, then have pump flow checked by a pump shop, who can determine pump make/model and specced flow. I need to look at everything one more time...probably spend a full weekend going over things slowly again. I'll provide an update later on, with fuller info.
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Old 10-12-2009, 11:15   #26
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Well Gang,
It has been a long day....winterizing the late-bloomers/die-hards.
As soon as I come in the door from the boats, this is the first page I go to.

With regards to the water flow issue, here is a link that will tell you what output you should get from your pump at what RPM.

http://www.johnson-pump.com/JPMarine...010_US_web.pdf

Aren't you glad you don't have to pay for this info.......you could always send a small contribution to.........
This is helpful info --thanks! Volvo Penta tells me I probably (but not for sure) have a Johnson pump --I need to verify.

In reply to your earlier post above --no, I don't have water heater plumbed into the cooling system, so no issue there (fortunately!)

I sure am glad I don't have to pay for this info! But, seriously, I hope to be able to provide advice and help to others (and do on other forums; I'm a newbie here). One of the things I love about boating is the community-mindedness of it --getting advice and info from folks, and being able to pass along my own advice/experience/help. Good karma. I appreciate your help! I'll definitely be way better informed the next time (I can't believe I said it!) I buy a boat with a diesel engine!
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Old 10-12-2009, 11:51   #27
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CHANGE THE IMPELLOR!

Don't ask, don't look. Just put in a new one!

Sometimes you can't tell from a quick look. They get worn, stiff, cracked etc.

My engines are bigger but the impellors get changed every year, no matter what. No problems.

The fastest way to send your engine to the grave is to overheat/overload it on a regular basis
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Old 10-12-2009, 11:53   #28
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Oh, is that the Big Johnson?
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Old 10-12-2009, 13:29   #29
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By passing 1/2 the exchanger

HI just a possibility I have an older Volvo MD30 which has a heat exchanger that is different than the Internals pictured by Volvo any way the raw water should normally enter at one end through ¼ of the tubes when it reaches the other end it is open to ½ the tubes so the water must travel back through the 2ed ¼ of bundle allowing more surface area, it then reaches the end and not able to escape so it travels back the length of tube ¾
Turns and travels through the last ¼ of the tube and out to exhaust elbow. My boat has a flat rubber washer at the opposite end of the heat exchanger entry which when the end cap is screwed in it causes a seal on the end of tubes to force water around. If this gasket is damaged it is possible to have the water travel through the 1st ¼ bundle and leak straight up to 4th ¼ and out the exhaust which would make your heat exchanger working only at 50%.
Note the models I have seen depicted in the Volvo parts do not have this 1/8” flat rubber plate but have achieved the directional flow through a Brass end cap.
Your Exchanger may be totally different. Just food for thought.
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Old 10-12-2009, 14:18   #30
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HI just a possibility I have an older Volvo MD30 which has a heat exchanger that is different than the Internals pictured by Volvo any way the raw water should normally enter at one end through ¼ of the tubes when it reaches the other end it is open to ½ the tubes so the water must travel back through the 2ed ¼ of bundle allowing more surface area, it then reaches the end and not able to escape so it travels back the length of tube ¾
Turns and travels through the last ¼ of the tube and out to exhaust elbow. My boat has a flat rubber washer at the opposite end of the heat exchanger entry which when the end cap is screwed in it causes a seal on the end of tubes to force water around. If this gasket is damaged it is possible to have the water travel through the 1st ¼ bundle and leak straight up to 4th ¼ and out the exhaust which would make your heat exchanger working only at 50%.
Note the models I have seen depicted in the Volvo parts do not have this 1/8” flat rubber plate but have achieved the directional flow through a Brass end cap.
Your Exchanger may be totally different. Just food for thought.
Thanks for the description/explanation. By any chance, does this diagram (exploded parts diagram of Volvo 2003 heat exchanger, which I have) look anything like yours? Thanks for your insights! (Click on "Heat exchanger" below.)

Heat exchanger

(I had to post the picture on a blog b/c this forum wouldn't allow me to upload the image...it's a .gif format pic, not a .jpg, and I don't know how to convert it.)
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