Mercruiser 260 Running HOTTT!!

[HeyMathison]

I'm at a serious standstill here with my boat running hot! Within a few minutes the boat starts redlining hot... I recently replaced the water pump, hoses, and impeller in the stern drive. Can annnnyone tell me what's going on here please?!?!? This is getting frustrating...

 

[JoLlY_RoGeR_ARRRR!!!!]

Re: Mercruiser 260 Running HOTTT!!

When you replaced the impeller was it in one piece? If not check for pieces throughout the cooling system.

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

For the most part it was. The ends of the rubber blades were missing though. I guess that would be a good start...

 

[JoLlY_RoGeR_ARRRR!!!!]

Re: Mercruiser 260 Running HOTTT!!

For the most part it was. The ends of the rubber blades were missing though. I guess that would be a good start...

Yep, I would bet that you will find those ends once you start looking. I am sure someone will be in here shortly that will give you good details on what to do as far as flushing and possibly "dissasembling". Good look!

 

[HT32BSX115]

Re: Mercruiser 260 Running HOTTT!!

Right after I got my 454/Bravo I asked the previous owner if he had changed the raw pump recently.

He said yeah, he replaced it the previous year......One would think everything was ok, right?

When I took the pump apart, it was "serviceable", but the housing looked a little "cooked" and the impeller, although intact, didn't look all that good either (he probably ran it dry for a minute or 2 .....that won't hurt it huh?)

But downstream of the pump, I found ALL the vanes of a previous impeller failure, literally CRAMMED into the oil cooler.

I'm surprised that it didn't over heat. (maybe it did)

They were large pieces and couldn't get past the oil cooler... so *some* water got past them.

Check your oil cooler, PS cooler (sometimes they are integral) and if you don't have either check the thermostat housing. Sometimes the vanes get crammed into the housing. If they get past the t-stat, they can go into the block and heads.


Regards,


Rick

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

Well yesterday we took it out around the lake for a quick lap to check to see how it was running and you could even smell a little burnt smell. The temperature rose pretty quick. Once we were back at the lift we loosened the thermostat housing to see if it was pumping water through the system. Water was spraying out there so im assuming that there is a decent volume flowing through.

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

I really appreciate all of your responses!

 

[HT32BSX115]

Re: Mercruiser 260 Running HOTTT!!

The water needs to be able to "get in" and it needs to be able to "get out" [FLOW]

If the raw pump is providing enough pressure/flow, and it's making it to the thermostat housing, then the water cannot get out because of {rust} clogged manifolds/risers (or even block/heads)

It's a very simple system. Do your risers get pretty hot quickly? (indication of insufficient water flow thru them)


We don't know what you have. Is it closed cooled or raw water? Power steering, oil cooler?


There's service manuals up above in the "Adults Only" sticky that actually have pretty good trouble shooting sections that address the very problem you have.




Regards,


Rick

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

It's a raw water system, and it's power steered. An oil cooler im not sure. I've had the boat for just a few days. The risers do get pretty warm... I guess the next step would to start taking things apart and cleaning them?

 

[HT32BSX115]

Re: Mercruiser 260 Running HOTTT!!

It's a raw water system, and it's power steered. An oil cooler im not sure. I've had the boat for just a few days. The risers do get pretty warm... I guess the next step would to start taking things apart and cleaning them?

The oil cooler is usually inline with the hose from the transom (raw water inlet)

If your risers (and/or manifolds) are clogged with rust, there's no safe way to clean them. They must be replaced.

 

[Bt Doctur]

Re: Mercruiser 260 Running HOTTT!!

If the large hose from the engine circ pump to the therm housing is hot on the bottom and cooler on the top ,you may have a broken shaft in the engine circ pump. Pull the engine circ pump, remove the back cover and look.

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

The circ pump was replaced Monday... I pulled the thermostat housing appart yesterday and replaced the gaskets due to the gaskets integrity. It was leaking slightly so I replaced the gaskets top and bottom. This boat has been ran without a thermostat for a while. I know on older vehicles it's not a problem at all to run without one. Well I read somewhere this morning that you should NEVER run a marine motor w/o one. I'm not sure if that would cause it to over heat or not...


Anyways, I still have a few questions on the water flow system. I am no mechanic so excuse me while I ask a few silly questions. The water is drawn in through the water inlets on the bottom stern drive with the impeller. It is then pulled through the stern into where? does it go through the water pump directly after? What's all considered to be the suction side and discharge side? Is it discharged through the risers and back out to the water?

If there is a flow chart somewhere that would be great lol...

 

[MikDee]

Re: Mercruiser 260 Running HOTTT!!

The circ pump was replaced Monday... I pulled the thermostat housing appart yesterday and replaced the gaskets due to the gaskets integrity. It was leaking slightly so I replaced the gaskets top and bottom. This boat has been ran without a thermostat for a while. I know on older vehicles it's not a problem at all to run without one. Well I read somewhere this morning that you should NEVER run a marine motor w/o one. I'm not sure if that would cause it to over heat or not...


Anyways, I still have a few questions on the water flow system. I am no mechanic so excuse me while I ask a few silly questions. The water is drawn in through the water inlets on the bottom stern drive with the impeller. It is then pulled through the stern into where? does it go through the water pump directly after? What's all considered to be the suction side and discharge side? Is it discharged through the risers and back out to the water?

If there is a flow chart somewhere that would be great lol...

From the water pump in the drive, the water goes into a special shaped 1" Mercruiser hose that leads to the transom plate (make sure this hose is not kinked at the transom plate under the outdrive) it happens!,,, Next it goes directly to the bottom of your engine water pump (it is the main water supply) if you have power steering, it may go through a power steering cooler first. You can take this hose temporarily off your engine pump while on the garden hose to check for flow, if you have good flow, this is not your problem. The normal thermostat on Mercruisers is 145* almost like no thermostat at all. Running on the garden hose, the temps usually never go above 160* if all is working right. The next things to check is your engine water pump, all the hoses, your manifolds, & risers, (do these get hot when you're running (boat in the water) you should be able to put your hands on the risers without burning them when it's all fully warmed up, & running.

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

Originally they were getting hot, before we changed the impeller and water pump. Now they are just warm. I am going to get a tempgun and shoot all parts and get a few readings at different rpms... When the boat is docked out of gear running at 3krpms it stays around 3/4 hot. If you drop it back down to idle it start's redlinging again. If you undock the boat and take it for a spin, it immediately redlines. It almost seems like in gear it's not getting water. This afternoon I will check that hose for a kink.


So where do the risers sit in the system? Suction or discharge side? I put a screwdriver between the boot and the pipe to see if there was any flow to that point. I couldn't really tell exactly how much volume was going through at that point but there was water spitting out.


From the water pump in the drive, the water goes into a special shaped 1" Mercruiser hose that leads to the transom plate (make sure this hose is not kinked at the transom plate under the outdrive) it happens!,,, Next it goes directly to the bottom of your engine water pump (it is the main water supply) if you have power steering, it may go through a power steering cooler first. You can take this hose temporarily off your engine pump while on the garden hose to check for flow, if you have good flow, this is not your problem. The normal thermostat on Mercruisers is 145* almost like no thermostat at all. Running on the garden hose, the temps usually never go above 160* if all is working right. The next things to check is your engine water pump, all the hoses, your manifolds, & risers, (do these get hot when you're running (boat in the water) you should be able to put your hands on the risers without burning them when it's all fully warmed up, & running.

 

[HT32BSX115]

Re: Mercruiser 260 Running HOTTT!!

The cooling system for a raw water cooled marine engine is pretty simple.

Think of it in terms of an engine that is full of water. The circulation pump is just that. It circulates water around the engine all the time.

The raw pump pumps fresh water to the engine and the manifolds and risers (where it exits with the exhaust.

If the thermostat is completely closed, the "raw" water just bypasses the engine and goes to each manifold and riser (under pressure) It fills each manifold and riser and then exits from the boat with the exhaust.

If the engine needs to cool a little, the thermostat will open and allow some of the water to enter the engines circulating stream to cool it......

What goes in must come out though(you cannot compress water)

The manifolds and risers are cast iron so they slowly rust internally. Eventually the rust begins clogging the passages in the manifolds and risers to the point where they'll restrict (water) flow. If you use it in salt it happens faster.

Manifolds and risers can last many years in a fresh water only boat. I think about 7-10 years max in a salt water boat that is flushed every time.


The risers are exactly that. they're mounted on the exhaust manifolds to be well above the engine ("rise") and waterline so they'll prevent any water from actually getting back into the exhaust system (into an open exhaust valve and hydrolocking your engine)


Exhaust gases and discharge water are "mixed" right where the large rubber hose connects to each riser and either goes to a "downpipe" or the thru-hull exhaust in the transom.

 

[MikDee]

Re: Mercruiser 260 Running HOTTT!!

Good info HT! By the way Mathison, the water supply hose in the outdrive, you have to turn the outdrive (the wheel hard right), & get down under, and look closely, to see anything, but up at the top of that hose, is a sharp bend into the transom plate (towards the motor), this is where you'll be able to see if it's kinked, & needs replacing. The Next item to check is the power steering cooler, (as was mentioned before) make sure it's not blocked, you can tell by taking the hose off, and checking flow like I said.

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

I now know exactly in what order the cooling system works. Thanks! The first thing I will do is check the hose to make sure it isn't kinked. Then place muffs on and make sure im getting water all the way through the system and back out through the exhaust. And thennn we will be taking the risers off checking the walls to check how corroded they are and how much wall is gone. After that, we will be removing the manifolds to check the conditions of the manifolds also. Wish me luck! If there is any good advice prior to taking any of this apart, or links feel free to givem!

Again Thanks For ALLLLL of the help and advice!

Water is compressible at high pressures and stabalized temperatures... Just figured I would let you know that.

I will give an update after this weekend. I will also post pictures of the risers and manifolds after they are apart.

 

[HT32BSX115]

Re: Mercruiser 260 Running HOTTT!!

Water is compressible at high pressures and stabalized temperatures... Just figured I would let you know that.

Well, I seem remember that from a Thermodynamics 1xx course I took many years ago..... but at the pressures we're talking about it's not significant! Your raw water pump is not capable of very much pressure....


By the way, riser gaskets are a real weak point in a marine exhaust system. You should pull the risers every few years and inspect them as well as the manifolds. You of course, then replace the gaskets too!

 

[HeyMathison]

Re: Mercruiser 260 Running HOTTT!!

OOOOKAY... Dissassembled the risers and looked in the manifold and the risers and they actaully looked to be in pretty good shape! Ran through everything that could possibly be wrong in the cooling system. Well we eventually figured out the problem @ 10 pm friday night and I almost feel like a big frickin dummy! The guy at the parts store sold me the wrong water pump! It was configured for ccw rather than cw... changed that and it ran cool as a cucumber. We went from one problem to another... I guess when we were running it hot we blew a head gasket and had oil coming out!!! So now we are busting all of that loose and changing gaskets on both sides. Besides being real careful and marking everything b4 we take it apart, is there anything else that we need to look at/for or keep in mind?

 

[MikDee]

Re: Mercruiser 260 Running HOTTT!!

I'm confused? Looking at the front of that engine 350/260hp it runs counterclockwise. Which is normal rotation for most small block Chevys, Or from the back of the engine it would be a clockwise rotation. Wouldn't a counterclockwise rotaion water pump be the right one to use?