Michigan Sportsman Forum banner

1 - 20 of 26 Posts

·
Registered
Joined
·
539 Posts
Discussion Starter #1
Today we were trolling on Lake Michigan. It was a calm day so the RPMs on the 4.3L I/O where low. Noticed the temp guage was reading 200 degrees and slowly rising. Puting the boat in nuetral and reving the engine imediately lowered the temp to 150 in about 5 seconds. Trolling again, temp slowly raised to 200 again. Same thing. Reving the engine imediately lowered the temp to 150. This happened one more time. We pulled lines and ran in. At the higher RPM's there was no problem. No problem also cruising the channel at 1500 rpm or so. At the ramp in neutral at a slow idle the temp started to rise again. We then shut her down.

Thought this was a classic sighn of a bad impeller. Replaced the impeller this afternoon. The old one "less that two years" looked great. Will try it tomorrow and see what happens.

Any thoughts about what else it could be.

Team "Bustin Caps"
 

·
Banned
Joined
·
4,684 Posts
Hmmmmmm..... Trouble shooting a boating problem... what fun!!!!

I have a buddy that is having the same problem on a 27' Amberjack, same motors. Starboard Motor Runs up to temp (145°), then creeps up to 200. Hit the Throttle and she instantly goes back to 145. We pulled the boat Sat afternoon and dropped the lower. The impeller was new last yr and looks new. We didn't get a chance to get into the 2nd thought (we went fishin'), but gonna inspect thet Check ball near the thermostat. The boat is an 88, so we're gonna take them out and check for rust/debris. Guy helping us was having the same problem on the same boat, but he only had to hit 900 rpm to get the motor to cool. He did the above, cleaning the check balls and he's all good.

If the impeller is good, make sure it is not installed backwards. If it doesn't str-8en itself out, that can cause a bad stream at low RPM. You can pull the inlet line off the power steering cooler and see if the impeller IS pumping a good flow. If it is, then the Next few things might be the culprit. Pull all your drain plugs in the block (manifolds, motor) to make sure there is no junk in there causing blockage. With the plugs out, run the motor and make sure there is good flow everywere. Next would be the Check ball. If that doesn't do it, might be the little flappie thingies (very techincal term) just on the outlet side of the exhaust manifold, near the elbow.


I will defeintly keep in this. I'll left you know what we find out.

BTW, we already did Thermostats......
 

·
Banned
Joined
·
4,684 Posts
It's rare for the circulationg pump on the motor to go bad. Don't get me wrong, they do go, but its not the norm. As a car, you would see water leaking around the pump housing, the pulley will have movement, and will usually have a bit of noise.
 

·
Registered
Joined
·
26,568 Posts
SalmonBum said:
It's rare for the circulationg pump on the motor to go bad. Don't get me wrong, they do go, but its not the norm. As a car, you would see water leaking around the pump housing, the pulley will have movement, and will usually have a bit of noise.
I have seen a couple that sand and crud had built up and reduced flow enough to cause it to get warm.
 

·
Banned
Joined
·
4,684 Posts
Good point Freepop.

Crud can be a problem, expecially on raw water cooled boats, that is why I made the comment above. Again, the pump doesn't go bad too often, but I will agree that if the motor is all crusted up, there could be a blockage in there too. If you have good flow coming outta the drain plugs while running, your circulation should be Ok. If your ports are clear, Impeller is good, check ball debris free, then I would look into the circulating pump.

What yr is the motor? How do u winterize the boat, just drain the block? Do you use anti-freeze? Is it just the -50°? If you goto the -60 or -100, they usually have a rust inhibitor in them that the -50 doesn't. Do you run the boat in shallow water? Was it ever a salty?
 

·
Registered
Joined
·
2,787 Posts
There is a 10 step test procedure to isolate overheating problems on my OMC by the maunual's instruction. I'm currently going through these tests (on my days off) trying to figure out why my engine overheated last year prior to sending it in for a new impellar which may be my next step depending on the results. Check the maint/repair manual and this should send you down the right path. Anything else as you saw in checking your impellar is only a guess. My overheating issues were completely opposite, cool at low RPMs and hot on the high side. So far I repaired the damage that had occured from the overheat, leak down test, rebuilt heads, head gasket replacement and now I'm trying to isolate the issue to one of the many areas that can cause the problem. When you pull your hoses and run at a lower RPM the flow should fill a gallon jug withing the percribed time indicated in the flow chart in the repair manual. There are other tests as mentioned above. It's an elimination by trial deal or vice versa you'll have to go through till you find the culprit.

I would break out the 25 bucks for the manual or borrow one if you can.
 

·
Banned
Joined
·
4,684 Posts
Hey Dan,

When you changed out the Impeller, did u change out the wearplate? I know on my old OMC I had an overheating problem. I had the mechanic put a new impeller in the fall before, so I thought it was something different. After pulling my hair out for 2 weeks, I bought a new one just to try. I found that he didn't change the wearplate and the grooves in it was leaking air, resulting in a low suction. New wearpalte, all was good.
 

·
Registered
Joined
·
26,568 Posts
Good point Bum. When changing the impellar, the housing should also be replaced. Most of the ones I've done had melted impellar on them and sealing would definately be comprimised.
 

·
Registered
Joined
·
2,787 Posts
SalmonBum said:
Hey Dan,

When you changed out the Impeller, did u change out the wearplate? I know on my old OMC I had an overheating problem. I had the mechanic put a new impeller in the fall before, so I thought it was something different. After pulling my hair out for 2 weeks, I bought a new one just to try. I found that he didn't change the wearplate and the grooves in it was leaking air, resulting in a low suction. New wearpalte, all was good.
Havent changed it yet... things just went from good to bad in a heartbeat. I launched over at that private launch on Muskegon. it was very shallow there and really should have gone out using the kicker. I may have just sucked up weeds & mud cuz I felt vibration shut down raised and lowered the drive and when I picked up speed, then no vibration leaving me to believe I slung the weeds off. I got up on plane and to the campground there and to the beach to pick up the family, through the channel and into the lake in about 2 to 3's about 4 miles out and noticed I was Hot hot. Temp said 190 :16suspect (yeah right) damn valve cover grommets melted and I cooked the valve guide seals. needless to say temp sending unit was tested,failed and changed. anyway I slowed it down and all was ok and it cooled right down so I shut down and checked things out, oil was ok and since it ran good at low R's continued to stay out monitoring everything. valve guide took most of the hit and the back of my boat was sooty but the engine none to worse for the wear and still ran great. Figured if it passed the leakdown it was worth fixing which it did and I fixed the damage, new head gasket and rebuilt the heads, shaved off 9thousanths off so there was some warpage. Now on to why it over heated. it runs ok on the hose but you cant get a true flow like that so I'll do the flow test using a big plastic tub for livestock trickling fresh water into it (beats launching it) and if it passes in the flow test then in the water it goes, if all is well then thats that, if not, then it goes to coldwater for the dinosaur mechanic to deal with. ie, probably a new impellar. I'd think the impellar or housing would be an issue but all along it ran 140 til I used the launch from hell. Anyways like I said earlier trial by elimination.
 

·
Registered
Joined
·
539 Posts
Discussion Starter #11
Its a 1994, so no checkvalve in the thermostate housing. Its my friends boat and he has had it only 2 years. Its never been in salt and it has always been drained by him (no crud in the block last fall) and antifreeze
put in by the marina (dont know what type.) Its never run in shallow water. That is if you dont count the St. Joe river channel in the spring.

Impeller didnt fix the problem. So went looking at the thermostat. The thermostat seemed stuck closed and the O ring on the bottom side was blown out and leaking past. Thought we had the problem solved. The over heating was not as bad though.

We are able to troll at slow speed now. Anything above about 700 RPM and the temp holds at 150 at the guage (thermostat is 140) Below 700 RPM and especialy at about 600 RPM the temp starts to climb slowly past 175.

I realize this is very slow, and below recomended operating RPM. But is this normal when the engine is running this slow?

appriciate your help

Eric
 

·
Registered
Joined
·
296 Posts
At those temps, is there really problem? Does the manual indicate a normal operating temp range? The 150-175 doesn't strike me as that high, but I'm no expert.
 

·
Registered
Joined
·
2,278 Posts
Try taking the thermostat out and run it, and see what happens. Test the thermostat, in a pan on the stove in water and a thermometer, make sure it opens when its supposed to. I have bought new thermostats that didnt work. Just a thought.
 

·
Registered
Joined
·
281 Posts
BUGBOAT said:
Today we were trolling on Lake Michigan. It was a calm day so the RPMs on the 4.3L I/O where low. Noticed the temp guage was reading 200 degrees and slowly rising. Puting the boat in nuetral and reving the engine imediately lowered the temp to 150 in about 5 seconds. Trolling again, temp slowly raised to 200 again. Same thing. Reving the engine imediately lowered the temp to 150. This happened one more time. We pulled lines and ran in. At the higher RPM's there was no problem. No problem also cruising the channel at 1500 rpm or so. At the ramp in neutral at a slow idle the temp started to rise again. We then shut her down.

Thought this was a classic sighn of a bad impeller. Replaced the impeller this afternoon. The old one "less that two years" looked great. Will try it tomorrow and see what happens.

Any thoughts about what else it could be.

Team "Bustin Caps"
I just had that same problem last week on my boat, it was the impeller, it now runs at 140 to 150.
 

·
Banned
Joined
·
4,684 Posts
Have you tried it since the new impeller install? Sounds like you may just be running the R's too low. The impeller only spins as fast as the motor rpm's, so if you’re too low, the thing might not be able to pump enough water. In a car you have a Fan kick on to simulate the wind if your stuck in traffic. A boat has nothing to help. Did u run the boat that low in the R's before with no problem? Maybe you running it that low for the 1st time to try the spring slow trolling? If you have not usually run that boat that low before that would be my guess, especially if everything is fine @ 700 or over. Regardless if this is the solution to the cooling issue, it’s not good to run that low of RMP's anyway. R's that low may not be able to keep safe oil pressure, on top of spline chatter, thought that is more of a concern with big HP V8's.

If you plan on trolling that slow, I would look into going down a pitch size on the prop. If you have a 17" now, go down to a 15. A quick way to explain it is a 17" should theoretically push your boat 17" forward per revolution of the prop. A 15 would push you 15". In return, you go slower with the motor working the same. My old boat would run 3.2 at idle with a 17. Switching to a 15 got me down to 2.0, with not adjustment in rpm.
 

·
Registered
Joined
·
5,111 Posts
SalmonBum said:
Have you tried it since the new impeller install? Sounds like you may just be running the R's too low. The impeller only spins as fast as the motor rpm's, so if you’re too low, the thing might not be able to pump enough water. In a car you have a Fan kick on to simulate the wind if your stuck in traffic. A boat has nothing to help. Did u run the boat that low in the R's before with no problem? Maybe you running it that low for the 1st time to try the spring slow trolling? If you have not usually run that boat that low before that would be my guess, especially if everything is fine @ 700 or over. Regardless if this is the solution to the cooling issue, it’s not good to run that low of RMP's anyway. R's that low may not be able to keep safe oil pressure, on top of spline chatter, thought that is more of a concern with big HP V8's.

If you plan on trolling that slow, I would look into going down a pitch size on the prop. If you have a 17" now, go down to a 15. A quick way to explain it is a 17" should theoretically push your boat 17" forward per revolution of the prop. A 15 would push you 15". In return, you go slower with the motor working the same. My old boat would run 3.2 at idle with a 17. Switching to a 15 got me down to 2.0, with not adjustment in rpm.
Good points on the low RPM equating to low oil pressure and high temps. It's best to stay within the manufacturers specs for idle RPM. As SB has stated changing to a lower pitch prop, will slow you down with out lowering the low end RPM. You must also be aware, that too low of a pitch will raise your WOT RPM. Stay within Specs. You do have to know your boat. If I'm going to be doing a lot of running I use a 17 pitch prop on my boat, and drop a drift bag to slow the troll down. I use a 15 pitch when I'll be trolling more than running. Those pitch numbers SB put out there, just happen to hit what I run.:)
 

·
Banned
Joined
·
4,684 Posts
Priority1 said:
You must also be aware, that too low of a pitch will raise your WOT RPM. Stay within Specs.
Yeah... forgot to type that. I know I was thinking of it when I was typing.....Thanks for catching that!

I think that motor WOT RPM's are 44-4600, but not positive.
 

·
Registered
Joined
·
2,470 Posts
For what it's worth, I have a 1986 Crestliner with 4.3 ltr i/o.
I can troll all day at 600 rpm without any overheating problems.
There has to be some other problem, it's not idle speed.
Rich
 

·
Registered
Joined
·
3,596 Posts
you should be looking at the inlet lines there will be one on the out drive going to the transom and then another inside the boat about 1 1/2' diam. they may have a pin hole in them. easy way to check is to get a clear piece of hose and put it in place of the inlet hose inside the boat. than run the motor u should see no air bubbles in this line. if you are seeing air it will tell you the problem is inlet side and you'll need to check impeller, housing and hoses.
only reason i mention this is for i have seen a clam tear a small hose in a line before and it was only a pin hole and i lost money that week working on that boat. and now with all the zebra up in the area i will bet they are going to cause mechanics and boaters alot of havoc
 

·
Registered
Joined
·
339 Posts
ok i may be making this too simple but what of the water intakes in the lower unit before the impeller, i believe you said all your problems started at the "launch from hell" is it possible that you have plugged the screens or the water inlets? mud weeds?


another possiblity that can cause a over heat problem is if your engine timing has been changed? possibly during a tune up by mistake?sometimes the hold down clamp for the distributor doesn't get tightened as much as it should then when someone changes a cap and rotor the accidently turn the distributor and knock out timing.
lastly i am a auto mechanic so i'm not sure if this will apply but the older 350 chevy engines had coolin water orfices in the intake gaskets if you put them on the wrong side it would over heat.hope i helped
 
1 - 20 of 26 Posts
Top