260 Mercruiser not cool enough- why?

[allyolds68]

Been watching this site and using the search function for years and I finally have a question that I can't quite pin down to one that's been previously asked

I've got a 83 245 Sea Ray Sundancer with a 260 Mercruiser (350 chevy). SEI SE106 drive. I've owned the boat since 1998. When I bought it it had a blown motor so I had a local guy put a remaned long block in it.


In 2006 I blew the motor. It had been running a little hot but never going into the the red. The day it blew I had a boat load of people and got it up on plane. The temp was slowly creeping up so I backed off and the temp immediately shot into the red so I shut it down to let it cool down. When I tried to start it it was hydrolocked (Didn't know it at the time and with a bunch of guests at the house I didn't have time to screw with it). Got towed back to my mooring. It was two weeks later by the time I got the boat towed to a launch and pulled it. There was water in pretty much every cylinder. It's raw water cooled and I was in salt water so the motor was junk.

I had a well known local shop do me a new stock motor. Everything in the motor was new, heads block, pistons, everything... I put on new risers (they were old and clogged, I thought this was why the motor blew) and cleaned out the exhaust manifolds (they were 2 years old) with acid and rodded them. When I got it all back together it was still running hot. I changed out the recirculating water pump and it ran fine. I have no idea why it made a difference because the water pump I pulled out looked fine. (I pulled the back plate off and the impeller was fine). I chaulked it up to a bad batch of water pumps and figured that contributed to blowing the motor. I ran it all that year (2007) in salt water but probably put less than 10 hours on it. I didn't put the boat in the water in 2008 or 2009. I ran it in 2010 in our new place in Upstate NY (fresh water) and it ran fine. Last year (2011) it seemed to be running hot again about 3/4 on the temp gauge as opposed to straight up middle, similar to what it was doing the last time the motor blew.

I've spent the last three weekends changing crap out and troubleshooting the "problem". It's got a new 160 degree thermostat, new drive water pump, new recirculating water pump, new "T" ball valves. A little more than $200 in parts but i've spent a lot of time on it.

I've run it with no thermostat (runs cool at all speeds). I've checked water flow from the drive pump, changed out the drive pump, removed the outdrive and ran direct to the motor (still at 3/4), Changed out the recirculating pump (still ran at 3/4).

Finally sick of throwing money at it and basically out of easy options I bought an infrared thermometer. With no drive on and water directly to the motor the temps seemed fine but the gauge is still at 3/4. It was 158 on the starboard side of the intake manifold, about 165 on the port. The problem appeared to be a bad sender and I never thought to run it up to 3000 RPM to check high speed. I put the drive back on with a new Sierra waterpump in it, put water to it and it runs the same temps at idle (right around 160). Then I ran it up to 3000 RPM and it runs at 160 on the Starboard side and 200 on the port side of the intake. The temp gauge moves slightly higher than 3/4... WTH.

Now it could be the waterpump in the drive isn't keeping up, but I doubt it. The sender is located on the starboard side, which apparently is the cooler side. My hose puts out 8 gallons/minute through the muffs. The old water pump was only putting out about 2 1/2 gallons/minute at any RPM which was too low. It's a two year old SEI SE106 drive. They have had issues in the past so that's why I put a brand new Sierra waterpump on it (plus it's not a bad idea to change at least the impeller every year anyway).

My gut tells me it's a head gasket but I pulled the plugs and there's no sign of water on them. there's no water in the oil so it's not leaking into the galley. For all I know 200 degrees is no big deal and it still might be the sender and I should just run the damn thing.

I've owned the boat since 1998 & know it pretty well but this has got me stumped. It's got the new style brass T ball thermostat housing. When it was running at 3000 RPMs (and 200 degrees on the port intake location) the exhaust manifolds and risors were less than 110 degrees anywhere on them (the manifolds were both about 110 aft and 90 fore, the risors were less than 100 degrees everywhere)

Opinions??

 

[achris]

Re: 260 Mercruiser not cool enough- why?

If you're running it at 3000 rpm on the hose you will be getting limited water flow. Engines should never be run more than about 1500 on muffs. Have you put a section of clear hose in the water line from the transom to thermostat housing? That will tell you a lot and either say where the problem is, or isn't. (Finding out what is not a problem is part 'n parcel of good troubleshooting)....

Chris...

 

[Cj7jeepoffroad]

Re: 260 Mercruiser not cool enough- why?

I've run it with no thermostat (runs cool at all speeds)

Sounds like a low flow issue, are you sure the thermostat is installed in the housing corectly?

 

[jopes]

Re: 260 Mercruiser not cool enough- why?

My engine was running warm and I found out the impeller was sucking in exhaust gas and not pumping enough water to the engine.

With you replacing so many parts and a new impeller make me wonder, did you do a whole pump kit or just the gaskets and impeller?

 

[BonairII]

Re: 260 Mercruiser not cool enough- why?

Sounds like a low flow issue, are you sure the thermostat is installed in the housing corectly?

I would also check for obstructions that could be limiting water flow.

 

[achris]

Re: 260 Mercruiser not cool enough- why?

I would also check for obstructions that could be limiting water flow.

That's the next step once a good water stream in the clear tube is established... At exactly 1000 rpm you should be pumping at least 4.0 qts in 15 seconds... This test MUST be done on the water, NOT on muffs...

 

[Failproof]

Re: 260 Mercruiser not cool enough- why?

If the infared thermo said 165, and the gauge said. "3/4" what temp is "3/4"? Go buy a 15 dollar mechanical temp gauge at auto parts store, and see what temps really are! If your current gauge says hot, but mechanical says not, then adios old lyin electric, hello new electric waiting to lie!

 

[allyolds68]

Re: 260 Mercruiser not cool enough- why?

First of all, thanks for all the quick responses. I know when someone new comes into a forum there's a tendency to not take as much time with responses as someone who's contributed in the past, that's clearly not the case here.

Sounds like a low flow issue, are you sure the thermostat is installed in the housing corectly?

Thermostat is mounted in the new style housing with the brass retainer above it. The o-ring is in place above it and the cork seal below. I cleaned out the thermostat housing of rust and scale although there wasn't much. And no, the thermostat isn't upside down.

Have you put a section of clear hose in the water line from the transom to thermostat housing? That will tell you a lot and either say where the problem is, or isn't. (Finding out what is not a problem is part 'n parcel of good troubleshooting)....

Chris...

My engine was running warm and I found out the impeller was sucking in exhaust gas and not pumping enough water to the engine.

With you replacing so many parts and a new impeller make me wonder, did you do a whole pump kit or just the gaskets and impeller?

That's the next step once a good water stream in the clear tube is established... At exactly 1000 rpm you should be pumping at least 4.0 qts in 15 seconds... This test MUST be done on the water, NOT on muffs...

You guys are all missing the fact that I've run it by bypassing the outdrive and running water directly to the motor with the same results. I've flow tested my hose directly (9 gpm), through the muffs (8.25 gpm), and the drive was originally only putting out 2.25 gmp (all at 1000 rpms). I know 2.25 gpm is too low and I replaced the entire drive pump assembly including the base with the Sierra unit. The pump I removed was in great shape. The impeller was fine and the housing was fine. I've backflushed from the motor back through the gimble housing with the drive off. There are no obstructions. I removed the power steering cooler, no obstructions. The only funky issue I have is in my outer gimble housing, directly after the face that the drives mates to, there's a significant cavity where the housing has corroded. It's not corroded through so water can escape but it could cause turbulant flow. But like I said, I had similar results on the gauge with the drive off the boat and the water connected directly to the motor.

If you're running it at 3000 rpm on the hose you will be getting limited water flow. Engines should never be run more than about 1500 on muffs.

If they motor shouldn't be run over 1500 rpms that makes sense. I guess the next step is to put it in the water and see how it runs. I thought that running direct to the motor at 9 gpm would be enough. I didn't mention that before replacing the T balls I did that too and it still ran at 3/4 on the gauge at 1000 rpms and creeped up higher when it was at 3000 rpms. This was before I bought the IR thermometer.

If the infared thermo said 165, and the gauge said. "3/4" what temp is "3/4"? Go buy a 15 dollar mechanical temp gauge at auto parts store, and see what temps really are! If your current gauge says hot, but mechanical says not, then adios old lyin electric, hello new electric waiting to lie!

I agree the gauge may still be an issue. The IR is a lot more accurate than a gauge that only measures in one spot.

No one has responded whether the 200 degree port to 160 degree starboard is an issue or what would cause this. If it's a bidirectional water pump equal amount of water should be delivered to each side of the motor. I assume even if the motor is starving for water, the temps should not be significantly different from side to side. I realize one side of the pump may be more efficient than the other so until it's in the water i won't know for sure.

Is there any simple was to check for a bad head gasket?

 

[Cj7jeepoffroad]

Re: 260 Mercruiser not cool enough- why?

The only funky issue I have is in my outer gimble housing, directly after the face that the drives mates to, there's a significant cavity where the housing has corroded. It's not corroded through so water can escape but it could cause turbulant flow.

Is it possible theres a hole in the intake side of cooling system? If it's sucking air it will cavitate the pumps at higher RPM's causing overheating.

Just shooting in the dark....

 

[coopin87]

Re: 260 Mercruiser not cool enough- why?

I've run it with no thermostat (runs cool at all speeds). I've checked water flow from the drive pump, changed out the drive pump, removed the outdrive and ran direct to the motor (still at 3/4), Changed out the recirculating pump (still ran at 3/4).


Opinions??

Why not just leave the thermostat out then. If you pulled thermostat and guage seemed to function correctly its not the guage or sender. If it runs cool 120' or so on muffs then just leave it out and drive the boat. Just my personal opinion but since the boat is raw water cooled I wouldnt run a thermostat anyway. Or If you want to keep the thermostat in it then buy a new one that opens up at a lower temperature. Thermostats dont particularrly like salt water. Just an idea.

 

[Scott Danforth]

Re: 260 Mercruiser not cool enough- why?

you have a blockage somewhere.

the Alpha raw water pump will top out at between 19 and 20 gpm (I assume the SEI 106 is similar) it wont take much to block the flow.

if your exhaust manifold is warmer on one side than the other, you have an issue there as well. Since your in salt water, I suspect the manifolds are shot

does your cooling system have an oil cooler? if so, check that as well for fouling.

do a leak down test to check for leaking head gasket. you can also pressure test the block.

 

[allyolds68]

Re: 260 Mercruiser not cool enough- why?

you have a blockage somewhere.

the Alpha raw water pump will top out at between 19 and 20 gpm (I assume the SEI 106 is similar) it wont take much to block the flow.

if your exhaust manifold is warmer on one side than the other, you have an issue there as well. Since your in salt water, I suspect the manifolds are shot

does your cooling system have an oil cooler? if so, check that as well for fouling.

do a leak down test to check for leaking head gasket. you can also pressure test the block.

I agree the original waterpump wasn't putting enough volume out. I haven't checked the new one yet but apparently I shouldn't run it over 1500 rpm on muffs so I won't be able to check it until it's in the water.

My exhaust manifolds are fine, at 3000 rpms my INTAKE manifold is 160 on one side and 200 on the other just before the thermostat housing.

I'm not in salt water now. The boat was only in salt water for one season (2007) and the manifolds only had two seasons in salt water on them. The exhaust manifolds and risers are all under 110 degrees

I'll look into a leak down test. I've never done one.

I'm not sure how easy it would be to pressure test the block. It's not a closed system so I envision a lot of fittings and block off plates

 

[Scott Danforth]

Re: 260 Mercruiser not cool enough- why?

also, you mentioned you bypassed the outdrive and ran the motor directly from the hose to the motor. this in turn fried your impeller without water running thru it.

I suspect you have something awry with your thermostat housing. your exhaust manifolds should be warmer than the engine itself. the fact that you have a temperature change from one side of the t-stat housing to the other would lead me to believe you have a blockage between the head and t-stat on that side.

 

[bobkat1864]

Re: 260 Mercruiser not cool enough- why?

Ya say she runs cool without the thermostat in place? Hmmm. I wonder, do you still have the temp imbalance that way? What about trying a cooler thermostat maybe?

 

[allyolds68]

Re: 260 Mercruiser not cool enough- why?

Why not just leave the thermostat out then. If you pulled thermostat and guage seemed to function correctly its not the guage or sender. If it runs cool 120' or so on muffs then just leave it out and drive the boat. Just my personal opinion but since the boat is raw water cooled I wouldnt run a thermostat anyway. Or If you want to keep the thermostat in it then buy a new one that opens up at a lower temperature. Thermostats dont particularrly like salt water. Just an idea.

Running without a thermostat masks a problem. The engine is still running hot there's just a greater volume of water passing through resulting in a lower temperature.

 

[allyolds68]

Re: 260 Mercruiser not cool enough- why?

also, you mentioned you bypassed the outdrive and ran the motor directly from the hose to the motor. this in turn fried your impeller without water running thru it.

I suspect you have something awry with your thermostat housing. your exhaust manifolds should be warmer than the engine itself. the fact that you have a temperature change from one side of the t-stat housing to the other would lead me to believe you have a blockage between the head and t-stat on that side.

I ran two hoses, one to the drive and another to the motor from different faucets on the house. I pulled that impeller as stated above and it was like new.

The thermostat housing has a bypass hole on the front which allows intake water to mix with hot water from the motor after the thermostat. With the thermostat housing off it's obvious that it's wide open in the intake manifold

 

[coopin87]

Re: 260 Mercruiser not cool enough- why?

Running without a thermostat masks a problem. The engine is still running hot there's just a greater volume of water passing through resulting in a lower temperature.

Also prevents damage. Greater volume is normally better. Might even help clear up whatever blockage he has. Many people run without thermostats in salt water. Granted it takes a bit longer for the motor to warm up but running without it on an open system should not hurt anything. Closed loop cooling is a different story though.

also +1 on SD's comment about hooking up staight to motor instead of outdrive (I would check the impeller again)

 

[allyolds68]

Re: 260 Mercruiser not cool enough- why?

Also prevents damage. Greater volume is normally better. Might even help clear up whatever blockage he has. Many people run without thermostats in salt water. Granted it takes a bit longer for the motor to warm up but running without it on an open system should not hurt anything. Closed loop cooling is a different story though.

also +1 on SD's comment about hooking up staight to motor instead of outdrive (I would check the impeller again)

I'll drill a couple holes in the perimeter of the thermostat to bypass.

As previously stated, I ran two hoses, one to the motor and one to the drive when I ran direct to the motor. I've pulled the waterpump since and it didn't have any damage but I replaced it with a Sierra pump kit since then

 

[coopin87]

Re: 260 Mercruiser not cool enough- why?

I'll drill a couple holes in the perimeter of the thermostat to bypass.

No need to drill holes just take it out completely. Just my opinion.

 

[Don S]

Re: 260 Mercruiser not cool enough- why?

No need to drill holes just take it out completely. Just my opinion.

Spoken like a true hack.:facepalm:

It fixes nothing, only covers up the problem so you don't notice it.

Removing the thermostat only makes the water flow faster past the sending unit. The back cylinders can actually be overheating because the water isn't there long enough to absorb the heat from the cylinder.