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View Full Version : Worn impeller vs. thermostat?



DJ13
07-29-2005, 10:07 AM
I'm running into a temp problem. I just replaced my water circ pump & serpentine belt in my 7.4l MPI. Now it seems my impeller has failed because I'm experiencing overheating. I just replaced the impeller a year ago. Do they go bad that fast? I thought the thermostat might need replacing as well. My questions:

1) What are the symptoms of a worn/bad impeller? I can idle all day and my temp stays between 150 & 180. Get on plane and after a while the temp slowly works it's way up and above 180 so I shut her down.

2) What are the symptoms of a bad thermostat? It's possible that the same thermo's been in there since '99.

3) When I flushed the engine last, I had a lot of water coming from the starbord exhaust pipe and barely any (just a dribble) on the port side. The boat is on a slight angle but that shouldn't cause more water to come out of one side. Any thoughts?

synack
07-29-2005, 10:55 AM
When my thermostat went out several weeks ago, it would run fine at low speed and at idle. But if you got on it for any period of time, the temp would spike and set off the alarm.

I have since replaced the thermostat and my normal operating range is usually between 165 and 175 on a 160 degree thermostat. The alarm doesn't kick off until 200+.

If you keep going, will it reach 200+?

If any doubts exist, just replace the thermostat. It's fairly easy and quick to do for peace of mind.

Donzi26ZX
07-29-2005, 11:05 AM
Check the oil cooler in the front of the motor. I just had the same problem with my 7.4MPI. Take off the top house and then the bottom hose and back flush the oil cooler, I had a ton of crap in there and now the boat runs perfect at 178 all the time. I replaced everything first before I got to this, new manifolds and risers (probably was due anyway) then I did the impellor and housing, (was due) and then finally I did the thermostat and that is when I realized that I should have checked the oil cooler first! GOOD LUCK!

cobra
07-29-2005, 11:08 AM
The water passages in the exh. may be clogged up, usually rust. If the water can't get out fast enough, new cold water can't get in so it'll raise the engine temp. Makes sence for the low water flow on that exhaust too. Exhaust manifolds can be cleaned of rust by soaking them in muriatic acid, eats the rust but not the iron. You can test this by running it and feeling the exhust manifolds for heat. They should be touchable, if they are too hot to grab with a bare hand they're not flowing enough, also they should be even temps. left & right. Since clogged water passages are a restriction, it'll affect high speed more than low. Hope it helps. Impellers rarely go out in a year unless you put on alot of hours, run in dirty water, or dry-run it. Thermostat it possible, but not likely for what you've described. If you find the exh. water passages to be the culprit, make sure to check all rubber exh. hoses (if you have them) as the extra heat may have damaged them.
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DJ13
07-29-2005, 11:11 AM
When my thermostat went out several weeks ago, it would run fine at low speed and at idle. But if you got on it for any period of time, the temp would spike and set off the alarm.

I have since replaced the thermostat and my normal operating range is usually between 165 and 175 on a 160 degree thermostat. The alarm doesn't kick off until 200+.

If you keep going, will it reach 200+?

If any doubts exist, just replace the thermostat. It's fairly easy and quick to do for peace of mind.

Yes it will reach 200+. I'm planning on replacing the thermostat now. I think I'll have to do the impeller as well or should I hold off?

txtaz
07-29-2005, 11:27 AM
General rule of thumb is to replace the impeller every spring. They will last longer depending on use. If they sit and dry out, it's best to replace it.
Wes

DJ13
07-29-2005, 11:30 AM
General rule of thumb is to replace the impeller every spring. They will last longer depending on use. If they sit and dry out, it's best to replace it.
Wes

I'm going to adopt that philosophy. They're not that hard to replace.

txtaz
07-29-2005, 11:34 AM
Ohhhh hey, I forgot to mention...I used to live in Bremmerton and work on the base there. Great country when it's not drizzling. Loved taking the loop around the pennisula and the ferries to Seattle for salmon. Any chance we can make a deal for some fresh salmon to be shipped down here???
Wes

DJ13
07-29-2005, 11:53 AM
Ohhhh hey, I forgot to mention...I used to live in Bremmerton and work on the base there. Great country when it's not drizzling. Loved taking the loop around the pennisula and the ferries to Seattle for salmon. Any chance we can make a deal for some fresh salmon to be shipped down here???
Wes

Hey Wes,

Yeah it's great country up here. Moved up from Napa California in 1979 and never looked back. Love summers! 80's and sunny!

I've never shipped salmon before but I'd be happy to look into that for you. What kind and what amount? ;)

Dave

MOP
07-29-2005, 03:53 PM
You say you replaced the impeller just one year ago, how much rubber was missing?
Point while we were up at 1K Tony developed a temp problem on his 16, I tore his sea water pump back off to find it in perfect condition. We went for a ride while I ran my hands over the engine and mainifolds looking for temp differential stbd manifold was atad hotter but nothing to get excited about, then as he throttled up harder water statred spewing from his risers joints. We went back in and I removed the risers, in the starboard riser there was an almost complete pump blade blocking one passage. He went out hunting gaskets for the Kodiaks but none were to be found so we ended up making new ones out of high temp Velimoid which worked very well. When ever a sea pump poops the bed it is important to find all the pieces, they will cause troulbe along the way. I am wondering if that what may be slowing the flow out of one side of your exhaust, in my yard where I flush I have about an 8" tilt it take my stbd riser 20-30 seconds longer to shoot water out but once wet they both shoot the same amount out.

Phil

gcarter
07-29-2005, 04:06 PM
Here's something to think about.
Since I added the sea water strainer, I've noticed the pump and hoses stay full of water, so the pump never starts dry.
Also the strainer basket in strainer housing catches all the crap and keeps it out of the coolers.

MOP
07-29-2005, 04:33 PM
On target as usual! George I was more then amazed at how much crap I pulled out of my strainer at 1K, 10 times more then at home! I can just imagine how much stuff hopefully went through the raw water cooled boys engines. I had to empty mine atleast one a day and three times on the 103 mile jaunt I took, most all of that run was at 3500 or better. So even at speed you do pickup crap out of the water. Every boat fresh water cooled or not should have a sea strainer.

Phil

joseph m. hahnl
07-30-2005, 10:57 AM
General rule of thumb is to replace the impeller every spring. They will last longer depending on use. If they sit and dry out, it's best to replace it.
Wes
oh my god you fell for that. what a gimick that is. that is a way for the marine shop to get money out of you every year. they told me i had to do that to my johnson out board too. it's had the same impeller since 1988 when i put the new motor on ." yes it's original" have never had any problems with it > "never ever"
it's 8 years old been thru winter summer many hours and no trouble.
"do i have super impeller"?,"i think not" it's just a gimick! one of those safe than be sorry. like don't drive your boat around you might hit a rock. keep it on the moring and it will always look pretty. sound rediculous don't you think!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

as far as the thermostate on this thread real good possibility. but i would agree with obstuction due to the diffrent amounts of water comming out of the exhaust."is it closed cooling" i found with my full cooler. you have to really fill it with coolant . meaning you let it sit a day and fill her up some more. they seem to gat air pockets in the block that you need to let bleed out.


joe

txtaz
07-30-2005, 11:22 AM
oh my god you fell for that. what a gimick that is. that is a way for the marine shop to get money out of you every year. they told me i had to do that to my johnson out board too. it's had the same impeller since 1988 when i put the new motor on ." yes it's original" have never had any problems with it > "never ever"
it's 8 years old been thru winter summer many hours and no trouble.
"do i have super impeller"?,"i think not" it's just a gimick! one of those safe than be sorry. like don't drive your boat around you might hit a rock. keep it on the moring and it will always look pretty. sound rediculous don't you think!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
joe
Uhmmm, Joe...I've owned boats for 35 years. Inboards and outboards. If you don't change your impeller soon, you'll be in the market for a new power head. Trust me, we owned a marina.
BTW, who said I took mine to a shop to have it done? I do the work myself. $20 impeller, a few beers and 30 minutes and I'm good for another year. The theory of "don't fix it if it's not broke" doesn't work here. So when you fry your motor, give me a call, I can tell you how to fix that also.
Ohh and next time you want to slam someone make sure you have your information correct. Personally, I wouldn't want to be out in your boat if the maintenance has not been done. Been there, done that...bought a shirt.
Wes

joseph m. hahnl
07-30-2005, 12:01 PM
Ohh and next time you want to slam someone make sure you have your information correct.


Wes: lets not have a moment. but i was not slamming you. my information is correct. and i don't need you to fix any thing for me. as a matter of fact i got you beat i've been on the water for 39 yrs. i was almost born on my fathers 1965 trojan 31. you can beleive what you want. that is the beuty of indipendant thought. but you should know i only speak fact from expierence.
Being a machinist i never ever base any thing on theory or conjecture. but actual physical fact on what it can due and what it has done. and WES if you don't want to come out in my boat. i can go out in yours. like i said i dont want to have a moment but i apologize if you thought that i was being hostile towards you.

joe

BUIZILLA
07-30-2005, 04:26 PM
I just bought a 302 Scarab with twin 1997 year 225 Johnsons, built in late 1996....

I just replaced the almost 9 year old starboard water pump kit this week, everything was ORIGINAL, dated 11/96, with 394 hours so far, and the impeller looked perfect, not even a stress kink anywhere. I was actually VERY surprised...

Just for grins, i'm going to do the port engine lower unit next.

I also just completely rebuilt the starboard lower unit myself with all new gears and bearings, due to some moisture, at some point b4 me. I will NEVER pay someone else again, after seeing how damm easy this was, even my Alpha bearing carrier puller worked. Ridiculously easy.

JH

cobra
07-31-2005, 01:50 AM
I hope not to fuel the fire here. New impeller every year is generally overkill, but it does make it safe. Kinda like jiffylube's 3 month/3k mile deally. Opps, may have started a new war now. I don't think I'd just ignore it for 10 years though. I check mine frequently cuz it's easy to get to and it's my time, not a billion $$$ to a mechanic who will tell me whatever makes him more dough. If I had to pay someone to do it I'd probably do the first one at 1 year like recomended, inspect the old one removed, & judge it from there. If you never suck sand, run in real dirty stuff, log a ton of hours, or dry run it, most would agree that it'll last WAY longer than a year, but not forever. And obviously, a few impelers are cheaper than a tow + rebuild.

txtaz
07-31-2005, 04:16 AM
Joe, Come on man...Let's have a moment. I haven't had a moment is such a long time. :biggrin: :biggrin:
The misses pointed out I was a bit touchy yesterday, so if my post was offensive, I appologize.
Now as far as maintenance on single engine boats. My philosophy is to do it every spring. It doesn't cost much and you'll have a reliable boat all season. On twins, you can run it till it breaks and limp home on one motor. I've seen water pumps last years also. I've also seen them break after 1 season. I prefer not to trust them when it comes to my enjoyment of off time especially when travel and expenses are involved. It is also important when boating is less traveled waters. Nothing like being stuck for 14 hours with no food or water waiting for someone to realize that your late getting home.
It's funny you mentioned a 31 Trojan. The first boat I learned to drive was a 31 Trojan. My Dad had one in late 60's early 70's. Great boat.
You are welcome on my boat any time.
Wes <<----- Moment over

Donzigo
07-31-2005, 08:58 AM
I would agree with all that's been posted. I have always replaced my waterpump impeller & housing once a year, sometimes twice. I also do all the other things mentioned here; and I've never had a break-down due to water overheating issues. These seems seem reasonable, prudent, easy to do, and is frankly "cheap insurance".

To: joseph m. hahnl.............great to read a post from a true professional. We don't get enough of that on this forum.

joseph m. hahnl
07-31-2005, 09:58 AM
To: joseph m. hahnl.............great to read a post from a true professional. We don't get enough of that on this forum. May we have another.[/QUOTE]

hey: are you mocking me?:eek!: any time buddy glad i could add alittle fuel to the fire.:splat:

you guys are way to easy. HA HA HA HA!!!!!!!!!!!!!!!!!!!!!!!!!!!!:hyper: :hyper: :hyper: :hyper:

ps: i allways love it when a parts replacer tries to tell me how it should be done.
joe

boatnut
07-31-2005, 12:36 PM
Back to your corners guys :biggrin: I have you both beat in time in boats, however I would like to be a lot younger and lose this race. I'm not a politician but I think the answer is the middle ground. Eight years is too long to go without changing an impeller and one year really is overkill with normal recreational usage. Of course, as has been mentioned, if you run in sandy conditions or run the impeller dry you can shorten the life quickly. I recently changed an impeller after 9 years of usage (although one week per year) and 3 flutes were missing and two others damaged. A cooling failure time bomb.
My rule (if anyone cares) is 3 or 4 years max unless I see a noticable reduction in water flow sooner. Ed

joseph m. hahnl
07-31-2005, 01:49 PM
Back to your corners guys :biggrin: I have you both beat in time in boats, however I would like to be a lot younger and lose this race. I'm not a politician but I think the answer is the middle ground. Eight years is too long to go without changing an impeller and one year really is overkill with normal recreational usage. Of course, as has been mentioned, if you run in sandy conditions or run the impeller dry you can shorten the life quickly. I recently changed an impeller after 9 years of usage (although one week per year) and 3 flutes were missing and two others damaged. A cooling failure time bomb.
My rule (if anyone cares) is 3 or 4 years max unless I see a noticable reduction in water flow sooner. Ed


i was exagurating: did i spell that right: any way if you do the math i've had the motor for 17 yrs. and it is on it's second impellor. and now thanks to all of you cursing me i will have to replace it because of all the bad karma you sent my way. but if I was running in the salt and running port to port in open sea with out a ship to shore : i most likely wouldn't not have let it go so long. but i run in fresh water and frankly the lakes aren't that big that i couldn't paddle back or ask for a tow. and i am allways watching to make sure
there is a steady stream of water> so as not to dwell on this subject i will shut up now> but the whole point that i was making is that it is doubtfull the problem is the impellor most likely the water would not even make it to the engine water pump> and thet there is obstuction some where > probably iron oxide in the outlet to the manifold : but as mop said about a broken piece he is usually right as is george is also so those are most likely the avenues i would follow> eneough said by me i shall never speak of it again>>>>>>>>>


joe

Donzigo
07-31-2005, 04:21 PM
joseph.............just teasing you a little. Hey dude, everybody on this forum is an expert...........including me........everybody thinks they do it right. Got any pictures of your engine/boat? ..................all those years on one impeller, you must be doing something right, for sure. I'm envious. HMMM......."parts replacer"......never heard of that term.

FYI: I run my boat over 250 hours a year & I'm running in salt, in an environment that's very shallow; so, I'm subject to lots of sand and muck. And, then there's this other thing. I love to work on my boat. Except for Scott Pearson, who paints his engine nuts ORANGE, I'm as excentric as they come.............anybody got a picture of those orange nuts to prove a point?

joseph m. hahnl
07-31-2005, 04:39 PM
joseph.............just teasing you a little.



i know you are!!!!!! beleive me i didn't take it the wrong way. if i couldn't take it i wouldn't dish it> so bring it on. a little tobasco in the omlete gets it going.

and remember you can never have to much water in a nuclear reactor!!!!!!!



joe

gold-n-rod
07-31-2005, 08:51 PM
......anybody got a picture of those orange nuts to prove a point?

Ahh yes, the downside of eating Cheetos and watching porn!!! :shocking: :shocking: :shocking:

DJ13
08-01-2005, 06:35 PM
You guys really crack me up! 2nd only to the knowledge offered up on this board is the sheer entertainment value of the wit and banter exchanged!

Well, I went ahead and replaced the thermostat, which was probably a good idea anyway, after all it's a '99 and most likely original...plus a cheap part. Then I back-flushed from the power steering cooler, to the oil cooler to the rear-most inline cooler (don't know what that one cools) and found out what was up. The obstruction ended up existing in that line and it was a big pile of sand, rocks and shells I must have picked up on the Columbia River a couple weeks ago. Made a nice big pile about 1&1/2 inches deep and now I recall how it happened.

Needless to say, the water started flowing again out the starboard exhaust pipe and I left the impeller alone. I have a new circ pump, thermostat and serpentine belt so things are good and THANK YOU for all your suggestions and guidance. :yes: I'm also keeping a spare impeller on board in the tool kit just for insurance purposes...

Hope there were no hard feelings or fueds started due to this post!! :shocking:

Donzigo
08-01-2005, 08:51 PM
Hard feeling or fueds............nah............this is kid stuff. Now you want to start a "blood fued", start asking those age old questions that we ALL got opinions about.................

Oil
Windsheilds or no windsheilds
Trailer tires
oh, and there's so much more.............

You bring up the srong subect, and you're on your own, dude.......if you can't take the heat, stay out of the kitchen.

PS: I'm glad you got your boat fixed............now, go replace that impeller
The "parts replacer" has spoken

thriller
08-02-2005, 12:32 AM
:beer: :pizza: :beer:

Wes,

Your Salmon delivery will be travelling with your Maple Syrup:)

MM