Mercruiser 305 V-8 Temp issues

[AnOldMedic]

depends on what thermostat 140 or 160

140 thermostat should be 150 or so

My 160 thermostat runs about 165-170

not being under pressure like in a automotive radiator they run cooler temps so it doesnt boil and lessens mineral scale buildup

I have the 140 thermostat.

 

[AnOldMedic]

As I think about things.
When I removed the exhaust manifolds, the starboard side bolts were all super loose. Like I didn't need to really put any pressure on the wratchet to get them out, same thing on the other side, with exception of the bolt where the rust was at, that one was rusted in place but still loose.
Not sure why they were loose, not sure how that would affect my running temps.

 

[Scott06]

I have the 140 thermostat.

then 180 is an issue. Did yo verify the thermo housing is actually 180 -200 with a IR gun?

As I think about things.
When I removed the exhaust manifolds, the starboard side bolts were all super loose. Like I didn't need to really put any pressure on the wratchet to get them out, same thing on the other side, with exception of the bolt where the rust was at, that one was rusted in place but still loose.
Not sure why they were loose, not sure how that would affect my running temps.

Not an issue only thing would be potential for exhaust leaks

 

[Scott06]

That's kind of what I thought, make sense because with the totally open OMC/Volvo set up the manifolds and elbows run really cool at idle, like 95-110* and a max of 135-140 only after coming off plane. Yet, I haven't seen signs of rusty exhaust valve stems when I pull the exhaust off for the normal checks we have to do in salt water (5-7 years).

I have had both style on Mercs and never noticed a difference.

 

[AnOldMedic]

then 180 is an issue. Did yo verify the thermo housing is actually 180 -200 with a IR gun?


Not an issue only thing would be potential for exhaust leaks

I did verify the 180 at the housing.

I am really not sure what gremlin I am chasing. I guess I am still looking for a blockage somewhere between the hull and the exhaust. I will be pulling all the hoses off to verify they are all clear, I will pull the thermostat housing off, and tear it apart to look, although I have a new one to put on.

Since I have the exhaust manifolds off, I am planning to change plugs and wires, should I do a compression test, since I have easy access?

 

[Lou C]

Ultimately your comp test may not be as accurate with a cold engine, you can try it though.
With a 140 'stat you should be within that temp give or take about 15-20 degrees. Even with the hotter 160 stat in mine I never ran at 180 unless there was a problem (clogged water intakes, sand sucked up that scored the impeller wear plate, things like that).

 

[Lou C]

I have had both style on Mercs and never noticed a difference.

You know I tried a 140 stat in mine because I always heard, oh in salt water you will get mineral build up with anything warmer. Well when I had the heads off to do the rebuild, I saw no such thing. I've seen pics of outboards with alu blocks with build up but not on the old cast iron block or heads.
The engine just took forever to warm up so I went back to the 160.

 

[AnOldMedic]

You know I tried a 140 stat in mine because I always heard, oh in salt water you will get mineral build up with anything warmer. Well when I had the heads off to do the rebuild, I saw no such thing. I've seen pics of outboards with alu blocks with build up but not on the old cast iron block or heads.

You know I tried a 140 stat in mine because I always heard, oh in salt water you will get mineral build up with anything warmer. Well when I had the heads off to do the rebuild, I saw no such thing. I've seen pics of outboards with alu blocks with build up but not on the old cast iron block or heads.
The engine just took forever to warm up so I went back to the 160.

Does anyone have the actual break down of the water pump in better detail than a parts diagram? Or a link to a video that shows piece by piece assembly. I am pretty sure I have an MR- here but I want to make sure I am using the right gaskets.
I think I didn't install #34 on the parts diagram, for the output tube, which is causing me to lose some water pressure. The plastic tube was pretty loose when I put it back in, ordered the whole new pump assembly, just want to make sure I put everything back together properly.

 

[Scott06]

Does anyone have the actual break down of the water pump in better detail than a parts diagram? Or a link to a video that shows piece by piece assembly. I am pretty sure I have an MR- here but I want to make sure I am using the right gaskets.
I think I didn't install #34 on the parts diagram, for the output tube, which is causing me to lose some water pressure. The plastic tube was pretty loose when I put it back in, ordered the whole new pump assembly, just want to make sure I put everything back together properly.

 

[AnOldMedic]

I did verify the 180 at the housing.

I am really not sure what gremlin I am chasing. I guess I am still looking for a blockage somewhere between the hull and the exhaust. I will be pulling all the hoses off to verify they are all clear, I will pull the thermostat housing off, and tear it apart to look, although I have a new one to put on.

Since I have the exhaust manifolds off, I am planning to change plugs and wires, should I do a compression test, since I have easy access?

Field UPDATE:
Here's where I am at.
All new exhaust manifolds, risers installed. All lines are clear to the lower unit. New water circulation pump installed. I have the thermostat pulled and rebuilding. Amazon sent me two new ones that were completely destroyed and missing parts. Another story.

I pulled my lower unit, here's what I found, and did not expect. Pics below. Melted plastic tube and water pocket heated with signs of heat, gasket was okay. The water pump was rebuilt last year.

Since I had the thermostat in the house and was cooking anyhow. I threw it in a pot of water. It opens at 182, it is clearly marked 140. Needless to say I ordered a mercruiser OEM one.

Side note, the lower pump part did not have the O ring on it, I know I put it on last season, but it is nowhere to be found. Impeller looked fine, and key was fine. I have a whole new OEM water pump coming this week. I am pretty sure I have all the gaskets in the right order.

I have the whole lower unit in the house, so the water pocket was easily changed out.

Thermostat order was - thermostat on housing, rubber gasket, brass insert.

Thoughts?

 

[Lou C]

I wouldn’t buy engine parts from Amazon because of how much counterfeit stuff there is out there. Merc parts are everywhere buy from a local dealer. Even with my Cobra where there isn’t the parts supply like for a Merc I use ONLY OEM for:
Bellows
Impellers & housings
Thermostats
I do use aftermarket for exhaust but Barr Marine is recognized as good aftermarket.
I’ve had very infrequent overheating issues and those were due to environmental conditions like sand sucked up scoring the wear plate or marine growth clogging the water intakes both easily solved. I always test thermostats before installing BTW. My engine with the 160 stat runs at 155-175 the higher temp is only seen after coming off plane.

 

[Scott06]

Field UPDATE:
Here's where I am at.
All new exhaust manifolds, risers installed. All lines are clear to the lower unit. New water circulation pump installed. I have the thermostat pulled and rebuilding. Amazon sent me two new ones that were completely destroyed and missing parts. Another story.

I pulled my lower unit, here's what I found, and did not expect. Pics below. Melted plastic tube and water pocket heated with signs of heat, gasket was okay. The water pump was rebuilt last year.

Since I had the thermostat in the house and was cooking anyhow. I threw it in a pot of water. It opens at 182, it is clearly marked 140. Needless to say I ordered a mercruiser OEM one.

Side note, the lower pump part did not have the O ring on it, I know I put it on last season, but it is nowhere to be found. Impeller looked fine, and key was fine. I have a whole new OEM water pump coming this week. I am pretty sure I have all the gaskets in the right order.

I have the whole lower unit in the house, so the water pocket was easily changed out.

Thermostat order was - thermostat on housing, rubber gasket, brass insert.

Thoughts?

You found your not smoking but melted gun. If you take your time and go back in with OEM parts you will have no issues. Would also check the condition of your exhaust flappers as they are likely melted too.

Obviously some one let it run without water at some point or maybe water tube wasn't seated and it was bypassing water. Exhaust will get really hot and melt stuff like the rubber connectors on exhaust system, plus the drive gets hot too.

There is a Quicksilver store on amazon that has legit OEM parts at amazon shipping speed, Also on ebay NuWave Marine (they just changed their name) is a quick ship. Leaders RPM in MI also sells on Amazon and Ebay. I get a lot of Merc and Sea Doo parts form them.

 

[Lou C]

I have also used Leaders RPM
I like my local dealer if a part is available he can get Merc, OMC or Volvo in a few days. I also use Marine Engine, and Lighthouse Marine supply here on Long Island.

 

[AnOldMedic]

You found your not smoking but melted gun. If you take your time and go back in with OEM parts you will have no issues. Would also check the condition of your exhaust flappers as they are likely melted too.

Obviously some one let it run without water at some point or maybe water tube wasn't seated and it was bypassing water. Exhaust will get really hot and melt stuff like the rubber connectors on exhaust system, plus the drive gets hot too.

There is a Quicksilver store on amazon that has legit OEM parts at amazon shipping speed, Also on ebay NuWave Marine (they just changed their name) is a quick ship. Leaders RPM in MI also sells on Amazon and Ebay. I get a lot of Merc and Sea Doo parts form them.

While I had the exhaust manifolds and risers off, I did check the flappers, they were in good shape.

I suppose it is possible when I put the upper back on I missed the water tube. This is the first time I have ever seen something like that.
Well like I said earlier, OEM only from now on.

I plan to put the unit back together on my bench to make sure I have a good proper fit, then install it back on the boat.

Does the upper drop out of forward gear as easily as the lower? and if so, How do I put it back into forward, never messed with the top half.

Thanks

 

[Scott06]

Does the upper drop out of forward gear as easily as the lower? and if so, How do I put it back into forward, never messed with the top half.

There is no shifting in the upper only the lower. It is just a right angle gear reduction.

When you shift into forward to reassemble put the prop on and use a bungee to hold it CCW. It seems counter intuitive because it is a RH prop- with pressure on it CCW it acts like the load water puts on it in use. This keeps the dog clutch from popping out if it is kept under load. You can turn the drive input shaft to get the splines to line up. when you install in the boat turn the prop to align the splines of the input shaft in coupler

 

[AnOldMedic]

There is no shifting in the upper only the lower. It is just a right angle gear reduction.

When you shift into forward to reassemble put the prop on and use a bungee to hold it CCW. It seems counter intuitive because it is a RH prop- with pressure on it CCW it acts like the load water puts on it in use. This keeps the dog clutch from popping out if it is kept under load. You can turn the drive input shaft to get the splines to line up. when you install in the boat turn the prop to align the splines of the input shaft in coupler

Great idea. Thanks.

 

[Scott06]

Great idea. Thanks.

thank @Bondo ... you didn't think I thought this stuff up on my own...