Mercruiser 260 HP OVERHEATING - Im Stumped!

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Just a thought from Meredith Neck. Could the motor be running too lean? That will over heat a motor also. Carb jets could be gummed up. It won't be your idle mixture screws. Are your plugs whiteish instead of tannish?

From what I can remember, the plugs were tan colored. I did look at them when I took them out last year and dont remember seeing anything abnormal. I did however blow out the electrode from the porcelain and the porcelain itself right out of the metal threaded housing last year (all at the same time). Thats when I replaced all the plugs. All the other plugs looked good. I have no clue what caused that. At first I thought it was a lean condition but never happened again and all the other plugs were ok.

That incident also blew the belts right off the motor.

 

[SC_Regal]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

I would try replacing the manifolds and risers. That is an old enough boat to have a problem. I'm in salt water - so a little different but mine started with similar problem- heat at high RPM. My search led me to manifold/risers. After replacement, problem fixed. Now if I could just fix my impeller.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

I would try replacing the manifolds and risers. That is an old enough boat to have a problem. I'm in salt water - so a little different but mine started with similar problem- heat at high RPM. My search led me to manifold/risers. After replacement, problem fixed. Now if I could just fix my impeller.

Im starting to think thats the problem too. I pulled them off and looked inside and they looked clear with a light coating of rust, but no flaking, clogging and caked rust particles. But I don't know what a good riser looks like either. I just assumed that because the risers weren't clogged with rust and had the same amount of opening as the gaskets that they must be good.

The boat is old, but it hadn't been used much. When I got it, the registration was 3 or 4 years old.

Do you think it's worth acid cleaning the risers and manifolds or just replace them?

 

[fraannk]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

oh snap,

You really need to try stretching the springs. I couldn't see how that would help but it has fixed my problem. My overheat was exactly the same as yours and I was resigned to spending the half a thousand dollars on manifolds. I figured I didn't have anything to lose and stretched the springs... viola! No more overheat. I really hope it works for you also!

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

oh snap,

You really need to try stretching the springs. I couldn't see how that would help but it has fixed my problem. My overheat was exactly the same as yours and I was resigned to spending the half a thousand dollars on manifolds. I figured I didn't have anything to lose and stretched the springs... viola! No more overheat. I really hope it works for you also!

Thanks Frank!!
I think you're right. I also think SC Regal is right. In my infinate wisdom (which isn't so infinate), I have put both of the last 2 posts together (it may be the vodka talking) and I think that the risers and manifolds are probably restricting the water flow as SC Regal mentioned. By stretching the springs as you mentioned, you are forcing more water to travel through the manifolds and risers, masking the real problem of the bad manifolds and risers, but curing the symptom of the overheating problem at high speeds. Soooo.... I am going to do just that and TRY to get this summer out of it and save my pennies for the cure next year.

I will let you know if this cures the overheating symptoms and I sincerely thank you (and everyone else) for the advice.

Will post the results as soon as I know. Probably next week (graduations all week this week).

 

[fraannk]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Actually, the manifolds and risers are working just great. The balls allow water to bypass the engine and go straight to the manifolds. If you stretch out the springs it gives the balls more resistance and the cool water doesn't bypass the engine anymore and allows it to circulate in the engine where it should be instead of bypassing because of the weak springs.

 

[fraannk]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

I didn't know any of that until last night when I found it on another post. There is a picture of it on this thread, post #44.

http://forums.iboats.com/showthread.php?t=383270&page=2&highlight=check+ball

 

[SC_Regal]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

don't acid wash the manifolds and risers. New ones are not that bad (all things considered). There are several options and several opinions about which ones to get - I think I got mine from ebasicpower.com. Just do your homework and make sure you have the right gaskets. For what its worth - when I was searching this topic the general consensus was that risers/manifolds needed to be replaced every 5-7 years.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Actually, the manifolds and risers are working just great. The balls allow water to bypass the engine and go straight to the manifolds. If you stretch out the springs it gives the balls more resistance and the cool water doesn't bypass the engine anymore and allows it to circulate in the engine where it should be instead of bypassing because of the weak springs.

Thanks Frank!

I do understand that. I did some internet research and saw how they worked but there is some contradictions between whether it causes an overheat problem at idle or at high speeds... what do you think?

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

don't acid wash the manifolds and risers. New ones are not that bad (all things considered). There are several options and several opinions about which ones to get - I think I got mine from ebasicpower.com. Just do your homework and make sure you have the right gaskets. For what its worth - when I was searching this topic the general consensus was that risers/manifolds needed to be replaced every 5-7 years.

Hmmm.... 5-7 year eh? Well, I bet we're a bit over that. lol. Thanks for the advice. I guess those risers may be bad even though they look ok to me. I am a car guy, not a boat guy, so the little bit of rust in there that I saw must be more than I thought.

 

[achris]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

4-6 years for elbows (incorrectly called 'risers') and 8-10 years for manifolds, if the engine is flushed after each use in salt.

The check balls ensure that the engine block (and heads) have priority for any cool water entering the system, after which any excess is directed to the exhaust manifolds/elbows, depending on the hosing of the system. Some use 'warm' manifolds which only get cooling water as a result of the thermostat opening and the water leaving the block will flow through the manifolds. 'Cold' manifolds have any cool water not going into the block directed to them, hence there usually run cooler, particularly at low engine speeds/loads.

Check balls stuck open could cause a low speed overheat by not forcing hot water out of the engine when the t'stat opens. Usually the water volume at higher engine speeds would provide enough water to keep the engine cool, even with the check balls open.

Just my 2c worth....

Chris..........

 

[Bt Doctur]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

It`s a long shot but you may want to check the impeller base gasket closely to see if this happened.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

4-6 years for elbows (incorrectly called 'risers') and 8-10 years for manifolds, if the engine is flushed after each use in salt.

The check balls ensure that the engine block (and heads) have priority for any cool water entering the system, after which any excess is directed to the exhaust manifolds/elbows, depending on the hosing of the system. Some use 'warm' manifolds which only get cooling water as a result of the thermostat opening and the water leaving the block will flow through the manifolds. 'Cold' manifolds have any cool water not going into the block directed to them, hence there usually run cooler, particularly at low engine speeds/loads.

Check balls stuck open could cause a low speed overheat by not forcing hot water out of the engine when the t'stat opens. Usually the water volume at higher engine speeds would provide enough water to keep the engine cool, even with the check balls open.

Just my 2c worth....

Chris..........

Thanks Chris!
I understand what you're saying but do you think that if the check balls were operating as intended and there was a restriction in the engine or manifolds (I believe I have the "cold" manifolds you refered to), the cool water could be pushed out at high speeds due to the increased pressure from the restriction?

I don't believe the check balls are getting stuck, I think the water is being pushed past them...

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

It`s a long shot but you may want to check the impeller base gasket closely to see if this happened.

Thanks! I looked at the photo and couldn't see anything. Maybe I need to check my glasses.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

One thing I should add is that the though hull exhaust pours out water heavy on one side and light on the other, but then changes sides. One of the reasons I suspect water is being forced past those check balls.

 

[achris]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

One thing I should add is that the though hull exhaust pours out water heavy on one side and light on the other, but then changes sides. One of the reasons I suspect water is being forced past those check balls.

Water IS suppose to be forced past the balls. But only when the t'stat is closed. When the t'stat is open the new cooling water goes into the block and the 'old' hot water runs past the t'stat and into the manifolds. When cool water makes the t'stat closed the excess cool water now not allowed into the block is forced past the balls and into the manifolds.

At this point in time (you've been looking for a while now) I would start thinking about putting a pressure gauge on the incoming water line. When the engine is idling you will see the t'stat open and close (pressure will be higher when stat closed, as the water must be forced past the balls). Run the engine faster and you shouldn't see any significant rise in pressure. A little is ok, but a lot will be indicating a blockage, like a manifold or elbow.

You need to do this on the lake, not on the flushers.

Chris.......
(EDIT.... I have just had another look at a water flow diagram for your engine. I am looking at Service Manual #9, page 6A-23. This would indicate you have warm manifolds. It also shows restrictor plates between manifolds and elbows. Now, if you have warm manifolds and the plates are missing, then that could force 'old' hot water being pushed out the elbows back into the engine and not allow the 'new' cool water in. Conversely if you do indeed have cold manifolds and the restrictor plates are in position, then you will definitely overheat at anything but idle.)

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Water IS suppose to be forced past the balls. But only when the t'stat is closed. When the t'stat is open the new cooling water goes into the block and the 'old' hot water runs past the t'stat and into the manifolds. When cool water makes the t'stat closed the excess cool water now not allowed into the block is forced past the balls and into the manifolds.

At this point in time (you've been looking for a while now) I would start thinking about putting a pressure gauge on the incoming water line. When the engine is idling you will see the t'stat open and close (pressure will be higher when stat closed, as the water must be forced past the balls). Run the engine faster and you shouldn't see any significant rise in pressure. A little is ok, but a lot will be indicating a blockage, like a manifold or elbow.

You need to do this on the lake, not on the flushers.

Chris.......
(EDIT.... I have just had another look at a water flow diagram for your engine. I am looking at Service Manual #9, page 6A-23. This would indicate you have warm manifolds. It also shows restrictor plates between manifolds and elbows. Now, if you have warm manifolds and the plates are missing, then that could force 'old' hot water being pushed out the elbows back into the engine and not allow the 'new' cool water in. Conversely if you do indeed have cold manifolds and the restrictor plates are in position, then you will definitely overheat at anything but idle.)

Thanks for all the info Chris!
Just an fyi: I currently have the tstat out but I havent tested it to see if water is still being forced past the check balls with it out.

I will do some testing next week with the information you gave me.

On your EDIT note:
I am not sure which manifolds I have. But I do have gaskets between the elbows and the manifolds that have a pinhole opening restricting the rectagle water flow port.... hmmm.

 

[John_S]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Thanks for all the info Chris!
I am not sure which manifolds I have. But I do have gaskets between the elbows and the manifolds that have a pinhole opening restricting the rectagle water flow port.... hmmm.

Not sure if your older engine has center rise style exhaust, but this is info that will help if you do have them. It was provided by Don numerous times in the past: http://www.boatfix.com/merc/Bullet/99/99_10.pdf

 

[fraannk]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

If you have a hose going to your exhaust elbow then you should have the small holes on two of the four holes on the gasket. The small holes go forward and aft. If you didn't have a hose going to your exhaust elbow then you would have the bigger holes in order to get cooling water from the manifold.

If you are running your boat right now without the thermostat you are just masking the problem. The engine is getting just as hot with or without the thermostat. When you take the thermostat out you are just allowing cool water to get to the thermostat without going through the engine. All you are doing is making it look like you aren't overheating but it is exactly the same as far as the temperature inside the engine.

I am not an expert. I was running without a thermostat and just figured out how bad it was for the engine. I hope I caught it in time. It never got so hot that it smelled hot so I think I am okay.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Not sure if your older engine has center rise style exhaust, but this is info that will help if you do have them. It was provided by Don numerous times in the past: http://www.boatfix.com/merc/Bullet/99/99_10.pdf

Thanks John!
I have the 863724 gaskets with 2 holes and 2 slots. I am not sure (even after reading that PDF if thats the right one for this engine. I think what confused me is that it talks about manifolds, risers and elbows. I thought risers and elbows were the same thing.

The engine serial number is the only number missing on this set up (of coarse) so when I order parts I dont have much confidence im getting the right parts.