Closed Cooling System on Port Engine Running Hot(ter)

[tpenfield]

I am on the 4th year of my (2) closed cooling systems on my twin Merc 7.4 LX MPI engines. They are the FULL version of closed cooling, so they do the block and the manifolds.

I added them to 16 year old 740 hour 'fresh water only' engines when I bought the boat up over at Lake Winnipesaukee in 2012.

The first 2 years of use were uneventful and both engines ran in the 155-165 F range all day long. so, no worries . . . I also have sea water strainers on the intake lines before the sea water pumps from day 1, so no crud would reach the heat exchangers.

Last year I noticed the port engine started to run a bit higher than it did previously (165-170) and took noticeably longer to 'recover' when going from cruising speed down to wake speed. The starboard engine was A-OK. I cleaned the sea water strainers to see if it made a difference, but it was minor if any.

Fast forward to this year, I filled both heat exchangers to start the season, as they were a few ounces low. The port engine is now running at 175-180, while the starboard engine is still at its original 155-165. Sooo, I think I should do something before it reaches 'the boiling point'.

Engines now have about 880 hours on them, so I have done about 45 hours per year in the first 3 years.

I'm going to take a look at the engines this weekend, but I thought I would put the question out here for some ideas and input.

My thoughts are:

Port heat exchanger is becoming clogged from sediment in the engine block . . .

Maybe the port engine thermostat is getting funky . . .

Some other kind of flow restriction on the closed side of the port engine cooling system.

Maybe even a flow restriction on the 'open' side of the cooling system.

What else should I consider/check ??? :noidea:

Also I am not sure about checking the rate of flow of 1 engine versus the other . . . :noidea:


Thanks in advance for any comments/suggestions. :thumb:

Serial #'s are in my Sig below.

 

[Scott Danforth]

Pull the end cap and look for fowling.

 

[Scott Danforth]

Ted, worse case, some crude is lodged in the glycol side between the tubes,

 

[FunInDuhSun]

Maybe change the raw water pump impeller? That's the first thing I would check.

 

[tpenfield]

Oh, sorry forgot to mention . . . new impellers this year. the old ones were 3 years old and in excellent condition when removed.

 

[tpenfield]

Thanks for the inputs, guys.

On Saturday, I'll have a few hours to mess with the cooling system. So, I thought that I would
1 - drain the coolant down a bit,
2 - remove the heat exchanger,
3 - remove the thermostat,
4 - take them back to the house for a test of the thermostat and a back flushing of the heat exchanger.

Then I'll put it all back together and take the boat for a spin. . . better get some more AF at wallymart , so I can top off the HE.

IIRC, the heat exchangers do not have end caps that can be removed, but I'll have to check.

Another thought that I had was that the only other difference (that I can think of) between the 2 engines is that the port engine runs the hot water tank for the sink/transom shower. I don't think it would matter if the heating coil in the water heater was clogged as the cooling system only routes a small by-pass line to the heater.

 

[Scott Danforth]

Marine HX's should have end caps to remove for clean out. about same diameter as the HX, single cap screw holding it on. you may be able to reuse the gasket, however I usually recommend new gaskets.

while at it flushing things, check the discharge into the elbows

my first suggestion is the end caps. you can do that while on the water.

 

[achris]

What are the engine exhaust elbows like? Restriction in either of those will lead to running hot and longer 'recovery time'... Is it running hotter at all engine speeds or just at higher power setting? I've even seen crud build up on the insides of the hoses (fresh and sea water sides), then flake off and cause blockages. Give the hoses a squeese. If they 'crackle' internally, maybe time to pull them all off and give them a very thorough clean out, and the rest of the system.... :facepalm:

Chris.........

 

[kbsunlovers]

You might swap the sensors & gauges between the two engines to see if the problem follows?

 

[tpenfield]

elbows . . . I can certainly check those as well. didn't really think about that.

they are the stainless steel variety, which I think got phased out shortly after 1996, when the boat/engines were made . I have Mercruiser OEM manifolds that were new in 2012 and only have run AF coolant through them, and the full isolating plate/gasket to separate the manifold from the elbow, then the SS elbows.

 

[tpenfield]

boy do I hate cooling problems . . . just as much as I hate electrical problems. :facepalm:

I took the heat exchanger off of the engine and brought it home to flush it. I did figure out the end cap disassembly and removed them to take a look at the internals.

No real build up in the heat exhanger and the coolant came out pretty much its original florescent green color. I also took a look at the exhaust elbows, the hoses, the oil cooler and they were all clear and in good shape.

Still the port engine runs 15+ degrees higher than usual. I even checked and re-fitted the connections at the gauge.

the only thing that I didn't have time to do was the thermostat . . . watch it be that :facepalm:

The exhaust elbows are only slightly warm after running a while and pretty much the same temp on both engines. So, I am thinking the coolant side is not circulating well enough on the port side.

Beyond the thermostat, I am out of ideas. I think that I might take Friday off and tear everything down again to check the thermostat, but all ideas welcome at this point.

I'll post a few pic soon.

 

[tpenfield]

Here are some pics I took of the work on the heat exchanger . . .


draining the AF down and removing the heat exhanger was not to difficult







Here are the endcaps removed.





I flushed both sides of the exchanger, but there really was not anything in there.

 

[Scott Danforth]

Ted, the one pic shows at least a dozen tube plugged in the end with the zinc. Looks like a combination of sediment and salt

Did you clean that?

Your running a 4-pass heat exchanger, anything more than 3 or 4 tubes plugged will start to affect performance

 

[achris]

Have the Heat exchanger cleaned by a radiator shop.

 

[tpenfield]

Ted, the one pic shows at least a dozen tube plugged in the end with the zinc. Looks like a combination of sediment and salt

Did you clean that?

Your running a 4-pass heat exchanger, anything more than 3 or 4 tubes plugged will start to affect performance

I didn't think there were too many holes obstructed, maybe a few, but I have some other photos that I will check. Thanks for pointing that out, I was not sure how sensitive the cooling is versus the number of tubes.

My original thoughts/plan was there was a bunch of engine sediment in the HE, but that was not the case. I am going to pull the HE (again) and the thermostat for another round of checking/cleaning.

Thanks Scott & Chris for your assistance :thumb: I had a similar issue with my F-242SS and it took a while to get it sorted out.

 

[tpenfield]

Ok, I checked my photos and googled "4 pass heat exchanger" . . . now I get it. There are about 6-8 holes blocked per the photos, but more importantly the "4-pass" means that the water routes several times back and forth, so even that few holes ends up being a greater percent of the overall flow.

 

[Scott Danforth]

If nothing came out of the glycol side, your dealing with sediment only on the raw water side. Since only the turn-around side (2-section divider) has most of the fowling, try to rinse it away, if needed, pass an aluminum welding rod in the tube from the side with the 4-section divider.

The tubes are copper, so take a bit of care.

 

[tpenfield]

If nothing came out of the glycol side, your dealing with sediment only on the raw water side. Since only the turn-around side (2-section divider) has most of the fowling, try to rinse it away, if needed, pass an aluminum welding rod in the tube from the side with the 4-section divider.

The tubes are copper, so take a bit of care.

Thanks, I'll break up the deposit and clear the holes. Any types of solutions/acids I should consider using to run through the tubes to reduce calcium deposits throughout the HE? Since I want to get the boat up and running for this weekend, I'll have to try some 'home remedies' rather than taking the HE to a radiator shop.

Also, I'll pull the t-stat for checking.

I am also wondering about the starboard engine and if it is starting to build up some deposits. :no idea:

 

[achris]

Radiator shop will drop it in a hot acid bath. Nothing you can duplicate at home. A radiator shop should be able to clean it out overnight.... (mine does. )

 

[Scott Danforth]

Kaboom and clr work