I can't solve overheat issue

[jamespjackson95]

Okay guys I can't seem to solve my overheat problem. I have a 1996 bayliner ski challenger with a 5.7 carbed Mercruiser. This boat is an inboard V-drive... After taking the boat out for the first time it ran great... Rode around at all speeds for numerous hours with no problems. Boat ran 170-175ish(right in the middle of my temp gauge). We decided to surf and loaded up about 2k lbs of ballast... We surfed for a few hours with no problems until..... Randomly while wake surfing the boat exhaust started to sound noticably louder (like the boat was running at a higher rpm).... Also there was more white exhaust smoke or steam coming out of the exhaust.... Then we noticed the gauge started warming up and near 200 we slowed down to an idle and it cooled off... Tried to start surfing again and it would immediately do the same thing (sound louder and then warm up)... That ended the day
I went home and checked the transmission cooler and found nothing, checked the Walter v drive for blockage and found nothing... Checked the water pump impeller and it looked fine. No missing blades(owner just replaced it).
The next day we went out to surf and all was fine for multiple hours. Then randomly started getting louder and overheating. At idle it would cool back down. I decide to pull the thermostat and it looked fine... With it out of the boat it ran 100 degrees and we continued to surf the rest of the day with no problems and ride around at all speeds with no problems. (Great I thought I found the problem)
The next day the boat ran 100 degrees for about an hour or so while surfing then just randomly the exhaust sound got louder and the temp gauge rose and we slowed down to idle and it cooled off... Tried to surf a couple more times immediately after that and everytime within about 30 seconds it would start to overheat... Then we pumped the ballast out and just tried to head back. Anything above about 5 mph would cause the boat to warm up... We tried 5 or so times and everytime it would warm up... But slow down to idle and it would drop back to 100...
So today I decide to pull the impeller and its brand new (I'm gonna replace it anyways). Also while the boat is in the water the hose coming from the impeller has 5-6inches of head(or water shooting straight up when removed... So good water going in). I pulled both of the risers off and they both looked pretty good. No major rust and no clog that I can see (although I didn't yet take the manifolds off). One of the down pipes looks like it had once got pretty hot and melted causing some restriction but hardly any for a 4" pipe. Just wanting some ideas of where to go next with this. See pics. I have checked all of the hoses and all seem to be fine with no bends or clog gage when running water though it. I am ordering a new thermostat(140) and a new thermostat sleeve and also new riser gaskets...
I have verified with an IR gun that the boat is actually overheating. Sorry for the long post. Just don't know what to do next.

 

[jamespjackson95]

 

[jamespjackson95]

 

[jamespjackson95]

 

[Fun Times]

You may possibly have a failing water circulating pump at the front of the engine....Or in your case at the rear of the boat.

 

[jamespjackson95]

You may possibly have a failing water circulating pump at the front of the engine....Or in your case at the rear of the boat.

I thought about this. However everytime I have ever seen one fail they have leaked water out of a little pee hole. Do you think my exhaust parts look fine? Is there any way to test the circulating pump? Would there be any down side to picking up an automotive one of it matched up 100%?

 

[jamespjackson95]

 

[produceguy]

I am no pro but I think your exhaust parts look fine. The impeller looks good but I would change it. I had a heat issue and my impeller looked good and I changed it anyway and it fixed the issue.

 

[Fun Times]

I thought about this. However everytime I have ever seen one fail they have leaked water out of a little pee hole.

Not always! While it is rare to read, the water circulating pumps internal impeller does eventually wear down from normal use. Sometimes they become entangled with debris. There is a stainless backing plate that you can remove to inspect the impeller once you remove the pump from the engine. Hope you don't have a head gasket issue but since there was a sign of an over heat at one time in the exhaust hose, you can not rule it out.....You might want to do a compression test with the engine as warm as you can stand it to work on. Leak down test as well.

Some other ideas as well for you, http://www.justanswer.com/boat/57upl-hi-i-mercruiser-5-7-engine-overheating-changed.html#

Do you think my exhaust parts look fine?

They all look good to me. But don't feel bad about checking them the way you did because with exhaust systems, you just never know until you have a look.

Is there any way to test the circulating pump?;

Not really without pulling it apart. Could try feeling the big hose for some pulsing of remove the big hose. Or here's what happens when you don't have the circulating belt connected,

Ok so here is the wierd, to me thing.
I decided to check water flow from all the hoses. Started at the transom water suply. diconected, started engine and watched for flow. had a good fllow of water comming out. disconected the suply at the Tstat housing and had good flow there. Disconected the hoses from the Tstat housing to the bottom of the exhaust mannifolds and had good flow there. Diconected the jumper hose from the exhaust Manifold to the riser, started engine and it took about 15 seconds before any water came out, but once it did there was good flow.
Now here is the wierd thing. i diconected the large hose from the Tstat housing to the engine water pump, there was very little water comming from the hose, still attached to the Tstat and alot of water comming from the engine water pump. How ever the temp did not climb and stayed at 150*. Hooked the the hose back up and the temp quickly rose to 180-200 then shut it off.
Its as if the water is going the wrong direction at the engine water pump? is this the result of the Tstat housing, or am i thinking of it *** backwards?
I disconected the suply at the tstat and no water was coming out either the engine waterpump nor the hose. alittle water was comming out of the exhaust tips at the transom . reconected the hose and then was getting a lot of water out the tips, but it was hot water, not warm.
http://forums.iboats.com/forum/engi...at-housing-tstat-and-gaskets-i-have-questions

Would there be any down side to picking up an automotive one of it matched up 100%?

Marine pump impellers are brass/bronze that hold up much longer running through any type of body of water you boat in. Auto pumps use a weaker material and will fail much sooner...Especially if you find yours to be bad.

 

[Richmond2000]

As a mechanic the comment the exhaust gets louder IMHO rules out cooling and my first thought is ignition timing going way retarded and the combustion is going down the exhaust causing a heat spike
beg-buy-borrow a timing light and take to the lake with you and check timing the next time it plays up

a different thought I know on a friends Jacuzzi jet boat the through transom exhaust had these flappers in the pipes to prevent sea water coming back into the engine
in a quick decal / throttle off condition and if one of yours has come loose maybe it is restricting the exhaust flow and that to would cause the exhaust to change noises and a heat spike as the hot gases are staying in the engine / exhaust system longer

 

[NHGuy]

Could be a timing issue is caused by the heat too. Overheat and load cause preignition /detonation. The knock retard system will hear clatter and pull out timing.
In fact there's a chance that a throttle chop with that load of ballast could have caused your original issue. If the lake water got to the engine it causes internal stuff to fail. Things like valves, head gaskets and who knows what else.
I'm not saying it's that for sure, but do the leak down and compression tests.
I hope it's only the engine water pump.

 

[jamespjackson95]

I must add the motor was rebuilt by jasper a few years ago because the manifolds leaked in the cylinders. They were replaced as were the risers.

 

[Scott Danforth]

Also while the boat is in the water the hose coming from the impeller has 5-6inches of head(or water shooting straight up when removed... So good water going in).

5-6" is nowhere near 20 psi

you should be able to fill a 5 gallon bucket in 16 seconds while at 1000 RPM.

 

[Scott Danforth]

also, the picture of the rubber boot shows the inside hide is burned away. this would be the result of less than adequate water flow. what you were hearing is probably parts of the hose coming loose while burning themselves and heading out your exhaust.

 

[jamespjackson95]

I will put everything back together and take it on the water today to check if it can fill a bucket... If I cannot fill the bucket do I replace impeller and re-test?
The wierd thing is it can go hours without overheating then randomly it decides it will overheat.

 

[jamespjackson95]

I was not able to lake test the boat today. I want to put the new impeller, thermostat and thermostat sleeve on(it broke when removing)....
When I removed the hose from the impeller that connects to the thermostat not only did water come forcefully out of the hose, it also came forcefully out of the thermostat housing where the hose was removed. This is probably normal but was just unsure if this would get us anywhere.
My boat is carbed however there is a safety system that will begin to alarm when the temp reaches about 200 degrees, and will not allow it to start until it cools back down....
Also everytime the boat overheats I have noticed the thermostat housing is extremely hot... Would this indicate a lack of water getting there in the first place?
I read some of the above recommendations and one was to remove air from the system... Does that apply to my engine?
i did a compression test a few weeks back and it was 165 on all 8 (like perfectly 165). Also I'm not sure how a leak down test works. Is it sort of the opposite as a compression test but put 15 or so psi into each cylinder? The oil has not went milkshakey or went down or up in the level on the dipstick. Not sure if this eliminates something.
The boat does not ever overheat until a few hours of riding around.

 

[dpoff]

Try pulling the engine circ pump and have a look at the blades?

 

[NHGuy]

So without starting the engine there was pressure in the cooling system?? That's a flag to check for clogs.