Mercruiser 260 HP OVERHEATING - Im Stumped!

[OhSnap]

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.

Thanks Frank!

I do have the hoses from the stat housing to the elbows and the gaskets with pinholes forward and aft.

Im a car guy, so taking out the stat was just a desperation move to not ruin the engine. I will put the stat back in next week when I do more testing.

 

[carcraze]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Can someone elaborate on running without a stat?

My understanding is that running with or without a stat will not change water path at all. Water still goes where it would normally go when the stat has opened. Running without one will also not cause an engine to overheat or cause a lower temp to be displayed while the engine is overheating.

What the ill effect is the engine takes much longer to reach temp and in fact if the cooling water is enough and cold it may not reach operating temp as it's job is to keep the engine from being too cold which has it's own set of unwanted problems.

This is my understanding of it's job, just wondering if my info is not correct?

Thanks

 

[John_S]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

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.

- Exhaust manifolds are what is bolted to the engine.

- Elbows are the 90 degree part that sits on top, and has a large rubber hose attached to the other end.

- Risers will be between the manifold and the elbows. Common for a 3" or 6" riser, but there are some boats that don't have them.

Center riser manifold means the riser is located mid-way between back and front of the exhaust manifold. If your riser is toward the back of the exhaust manifold, it is commonly called a "log" style.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

- Exhaust manifolds are what is bolted to the engine.

- Elbows are the 90 degree part that sits on top, and has a large rubber hose attached to the other end.

- Risers will be between the manifold and the elbows. Common for a 3" or 6" riser, but there are some boats that don't have them.

Center riser manifold means the riser is located mid-way between back and front of the exhaust manifold. If your riser is toward the back of the exhaust manifold, it is commonly called a "log" style.

ok, I dont have risers, thats why I didn't understand what they were.

The elbows are mounted to the center of the manifolds.

 

[fraannk]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Carcraze,

I know for a fact that it makes a difference with or without a thermostat as far as the temperature indication.

Look at the schematic of the water flow diagram on these thermostat housings. The water takes the path of least resistance. It comes in from the lower port side through a hole into the lower starboard side and out to the water circulating pump. The water then circulates through the engine and comes back into the thermostat housing through a hole in the block right under the thermostat and mixes with the cool inlet water. If the thermostat is open then a metered amount of water is allowed to go out to the exhaust manifolds through the aft hoses on the thermostat housing. The temperature gauge reads the temperature of the water as it comes out of the block. The top forward hoses also send a metered amount of water (metered by the tension on the balls) to the exhaust elbows.

Now, if you take out the thermostat... the water takes the path of least resistance from the inlet side which is a wide open hole right to the exhaust manifolds. It just so happens that the water temperature sensor is right in line with that flow. I guess if you were to put a restriction plate in place of the thermostat that let out the amount of water that the thermostat allows when open then you would be able to see the true temperature of the water as it comes out of the block.

Again, I am not an expert by any means. I have just spent a lot of time on this because my engine was having the same problem.

Frank

Edit: corrected flow to the manifold and elbows and added that water out of block mixes with incoming water.

 

[carcraze]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

ai do not want to hijack here.
I am not sure the set up you have but I was under the understanding tha t with the stat closed once the water leaves the block after the circ pump has pumed it through then some of the warm water is mixed with the incoming andgoes back through th block while some goes out to the elbow via the check ball fittings as they are the forward ports. Once the stat opens water is then directed out through the exhaust manifolds and some through the elbows depending on presure to open the balls???

Mind you I believe the set up I have is that way.

 

[fraannk]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Thanks carcraze, I have edited my post to be correct. I mixed up the manifold and elbow flow. Now I have to head to the lake until Saturday so you guys have fun discussing what else I got wrong.... =).

 

[Bt Doctur]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

The base gasket is installed wrong,easy to miss cause it fits both ways.Found it AFTER the cust said HE changed the water pump assembly.no more overheat.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Carcraze,

I know for a fact that it makes a difference with or without a thermostat as far as the temperature indication.

Look at the schematic of the water flow diagram on these thermostat housings. The water takes the path of least resistance. It comes in from the lower port side through a hole into the lower starboard side and out to the water circulating pump. The water then circulates through the engine and comes back into the thermostat housing through a hole in the block right under the thermostat and mixes with the cool inlet water. If the thermostat is open then a metered amount of water is allowed to go out to the exhaust manifolds through the aft hoses on the thermostat housing. The temperature gauge reads the temperature of the water as it comes out of the block. The top forward hoses also send a metered amount of water (metered by the tension on the balls) to the exhaust elbows.

Now, if you take out the thermostat... the water takes the path of least resistance from the inlet side which is a wide open hole right to the exhaust manifolds. It just so happens that the water temperature sensor is right in line with that flow. I guess if you were to put a restriction plate in place of the thermostat that let out the amount of water that the thermostat allows when open then you would be able to see the true temperature of the water as it comes out of the block.

Again, I am not an expert by any means. I have just spent a lot of time on this because my engine was having the same problem.

Frank

Edit: corrected flow to the manifold and elbows and added that water out of block mixes with incoming water.

Thanks Frank!
I wondered if the thermostat played a role in keeping pressure in the right places and I think that answered the questions I have about the tstat.

Do you think if I put the tstat back in the engine will still overheat?

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

The base gasket is installed wrong,easy to miss cause it fits both ways.Found it AFTER the cust said HE changed the water pump assembly.no more overheat.

Hmmm.... ok I get it.

Is there a way to measure the water coming from the lower unit? I would assume there should be an X amount of GPM. When I remove the hose from the lowerr unit and run the engine it appears I have decent flow. I would guestimate about 3 gallons a minute.

 

[dirtyoldman]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Hmmm.... ok I get it.

Is there a way to measure the water coming from the lower unit? I would assume there should be an X amount of GPM. When I remove the hose from the lowerr unit and run the engine it appears I have decent flow. I would guestimate about 3 gallons a minute.

If you have the thermostat out you could put a pair of vice grips on the hoses from the check balls. That would close them off and remove from consideration. What is the water temp going out of the engine? I would start pulling hoses and seeing where the water is coming out, at what volume, and at what temperature.

I went through the overheat at idle and had fogotten to put the check balls back in.


I have heard of the hose getting kinked through the outdrive. I'd look that over very well. It seems mine pulls more than 3gpm through it, but I could be wrong. I think I have 2.5 gpm shower heads and am pretty sure my boat dumps more than that. I'd really like to hear what the temperature of the discharge is, ang the temperature of the two hoses going to the exhause manifolds.

It also might be time to pull the water pump off the engine and see how the impeller works and try to back flush the block, see what comes out and if there is any blockage there. While the water pump is off the block you need to put one end in a vice and see if you can turn the impeller on the shaft. If so, that's your problem. Under higher load (higher RPM) the impeller could be spinning on the shaft and not moving enough cooling water through the block.

 

[achris]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

This is your water flow diagram. From what I can see the restrictor plates may be restricting too much. As a test I would remove them and see how you go. As a long term fix, if it was mine, I'd remove the plates all together, plug the hole in the front of the elbows and join the hoses from the top of the t'stat housing to the hoses that run to the bottom of the manifolds. That will convert the system from warm manifolds to cold manifolds, and allow a much easier flow path for the water, while keeping the manifolds a lot cooler.

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.

Just checked up on the parts listing, and Merc DO NOT list a restrictor gaskets, just a normal one, 27-863724. This is what the gasket should look like.

Chris......

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

If you have the thermostat out you could put a pair of vice grips on the hoses from the check balls. That would close them off and remove from consideration. What is the water temp going out of the engine? I would start pulling hoses and seeing where the water is coming out, at what volume, and at what temperature.

I went through the overheat at idle and had fogotten to put the check balls back in.


I have heard of the hose getting kinked through the outdrive. I'd look that over very well. It seems mine pulls more than 3gpm through it, but I could be wrong. I think I have 2.5 gpm shower heads and am pretty sure my boat dumps more than that. I'd really like to hear what the temperature of the discharge is, ang the temperature of the two hoses going to the exhause manifolds.

It also might be time to pull the water pump off the engine and see how the impeller works and try to back flush the block, see what comes out and if there is any blockage there. While the water pump is off the block you need to put one end in a vice and see if you can turn the impeller on the shaft. If so, that's your problem. Under higher load (higher RPM) the impeller could be spinning on the shaft and not moving enough cooling water through the block.

Thanks!
I did check the hose from the outdrive for kinks and didn't see any problems. I also checked the hose from the hull to the engine and that looked ok as well.

I measured the water temp coming out at idle and it was around 100 degrees at the end of the pipes. I cant measure it when there is a problem (high speeds) for obvious reasons.

The water pump is new. Last year when the problem started. I did hear a metal squeeling noise that sounded like metal spinning on metal and thought it was the water pump. When I took it off it seemed fine though... replaced it anyway.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

This is your water flow diagram. From what I can see the restrictor plates may be restricting too much. As a test I would remove them and see how you go. As a long term fix, if it was mine, I'd remove the plates all together, plug the hole in the front of the elbows and join the hoses from the top of the t'stat housing to the hoses that run to the bottom of the manifolds. That will convert the system from warm manifolds to cold manifolds, and allow a much easier flow path for the water, while keeping the manifolds a lot cooler.

Just checked up on the parts listing, and Merc DO NOT list a restrictor gaskets, just a normal one, 27-863724. This is what the gasket should look like.

Chris......

Thanks Chris!
That is the same gasket I installed on the elbows for sure. Looks just like it and I even checked the part number on my receipt.

Thanks for the idea of converting the manifolds. Do you think this is just the manifolds/elbows getting hot? If I send cooler water to those parts will the engine itself run hotter? Also, just to be clear, are you talking about using the the hoses with the check balls for the bottom of the manifolds?

 

[achris]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Thanks Chris!
That is the same gasket I installed on the elbows for sure. Looks just like it and I even checked the part number on my receipt.

That's good.

Thanks for the idea of converting the manifolds. Do you think this is just the manifolds/elbows getting hot?

No. the temp gauge is not lying

If I send cooler water to those parts will the engine itself run hotter?

Agina, no. The temp of the manifolds has no bearing on the temp of the engine

Also, just to be clear, are you talking about using the the hoses with the check balls for the bottom of the manifolds?

Close off the fitting in the elbow. Then have both the hoses from the t'stat housing (including the ones with the balls) go to the bottom of the manifold.

This is what I'd do.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

That's good.



No. the temp gauge is not lying



Agina, no. The temp of the manifolds has no bearing on the temp of the engine



Close off the fitting in the elbow. Then have both the hoses from the t'stat housing (including the ones with the balls) go to the bottom of the manifold.

This is what I'd do.

ok, I will try that as well... Thanks for all the help

 

[dirtyoldman]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

ok, I will try that as well... Thanks for all the help

I really thought it was the water pump. I would start removing hoses nd timing how long it takes for the water to fill a five gallon bucket. I'd start at the pump from the lower unit and time that, then pull off each of the four small hoses coming from the thermostat housing and take the same data. I think this will help tell you where the restriction is, or whether the water is just bypassing the thermostat housing and engine block all together.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

I really thought it was the water pump. I would start removing hoses nd timing how long it takes for the water to fill a five gallon bucket. I'd start at the pump from the lower unit and time that, then pull off each of the four small hoses coming from the thermostat housing and take the same data. I think this will help tell you where the restriction is, or whether the water is just bypassing the thermostat housing and engine block all together.

Yep, me too.

I did plan on measuring water volume next week if we have decent weather.

 

[OhSnap]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

Yep, me too.

I did plan on measuring water volume next week if we have decent weather.

Still scratching my head on this one....

I messed with it today and would like to add that the belts tend to slip and squeel at anything above an idle also. So now im wondering if anyone knows what the possibility is that there might be a blockage in the engine block somewhere, causing excess pressure to build up at the circ pump, making the pump work harder and making the belts slip.

Is this possible???

 

[NHGuy]

Re: Mercruiser 260 HP OVERHEATING - Im Stumped!

So pull off the belts and give the circ pump a spin. In fact spin everything, if there are any pulley driven devices holding things back it can interfere with your water flow. They should turn smoothly and quietly. If not, investigate.