Risers Running Hot Skipjack 20

[fv_ghostdog]

I noticed a couple weeks ago that the risers were pretty hot when running in the driveway for 5minutes. Decided to change the thermostat and impeller. This is a 2019 Marine Power 350 Vortec Chevy on my 1982 Skipjack 20 Open.

The thermostat housing is weird on my motor. It had a plastic spacer that keeps the thermostat suspended above the motor. See picture. Usually on cars, the thermostat sits right on top of a gasket that meets the motor block.

If you have a Marine Power 350, or something similar to my I/O, and you are trying to remove the plastic spacer from the t stat housing, then gently pry out with a flathead. Notice that there an indentation in the side of the spacer, so it only gets inserted one possible way. There is a cork gasket you must order and insert into the housing first before seating the t stat, and then the plastic casing. There is also the typical gasket that goes between the t stat housing and motor. Below are part numbers for my specific setup, and may apply if you have a Merc 350.

After changing the impeller and t stat, I ran the boat in the driveway again. The 143 degree t stat opened up and was steady at around that temperature. But after 5 minutes the risers got hot again. A couple buddies told me that the hole in the back of my whale tail (bottom back side of my Volvo 280 outdrive) needs to be plugged. I never knew this.

They used a bolt wrapped with electrical tape to plug there's. This is only plugged when running your boat in the driveway. Another buddy said that a sharpie marker fits snug. I will try this week and report back. See picture of where I point to the hole at the back of outdrive lowr unit.


Parts used for my Marine Power 350 ordered from MarineEngineDepot:
● 4.3L / 5.7L / 7.4L Thermostat to Engine Gasket GM 10105135
SKU: 280153
●4.3L/262ci - 8.2/502ci Raw Water Cooled Thermostat Spacer 5042-001
SKU: 515645
●4.3L/262ci - 8.2L/502ci Thermostat 143 Degree 200-140
SKU: 515400
●Raw Water Thermostat Housing Gasket
SKU: 0212-002

Helpful install video:

 

[fv_ghostdog]

Any official name of that Water port hole? And any other recommendations on what to use to plug it? Thanks.

 

[fv_ghostdog]

Also, I soaked the t stat housing and the bolts in saltaway for a couple days before reinstalling it. Also cleaned up around where the housing meets the motor to remove any of the old gasket residue. I used a putty knife with a rag wrapped around the blade to prevent scoring the metal.

 

[slater]

how old are the exh manifolds?
They dont last forever & can result in grenading your engine....

 

[SilentViper]

I'm assuming you're running muffs? In my experience running my VP in the driveway is the hose can't provide as much water as the impeller pump will consume.

I added a Tee between the outdrive standpipe and the strainer on my setup; so i dont have to fuss with muffs and it seems to do a better job than the muffs do. any extra hose pressure gets bled off through the outdrive but the pump can consume as much as it wants. Risers will be warmer than when it's actually submerged in a lake/ocean but not hot to the touch.

So far so good.


But slater is 100% on point, check those things annually in my opinion. a rust pinhole in the wrong place can fill a cylinder with water.

 

[fv_ghostdog]

how old are the exh manifolds?
They dont last forever & can result in grenading your engine....

I am actually not too sure. The previous owner passed away and it was his kids who sold me the boat and didn't know much. From the paperwork it seems he repowered in 2019 to a new motor. I'm guessing the risers are same year.

 

[fv_ghostdog]

I'm assuming you're running muffs? In my experience running my VP in the driveway is the hose can't provide as much water as the impeller pump will consume.

I added a Tee between the outdrive standpipe and the strainer on my setup; so i dont have to fuss with muffs and it seems to do a better job than the muffs do. any extra hose pressure gets bled off through the outdrive but the pump can consume as much as it wants. Risers will be warmer than when it's actually submerged in a lake/ocean but not hot to the touch.

So far so good.


But slater is 100% on point, check those things annually in my opinion. a rust pinhole in the wrong place can fill a cylinder with water.

Interesting. What do you mean by Tee that you added?

I have seen some guys submerge in garbage can full of water. Is that recommended over the muffs? I do use the muffs.

 

[SilentViper]

Interesting. What do you mean by Tee that you added?

I have seen some guys submerge in garbage can full of water. Is that recommended over the muffs? I do use the muffs.

i essentially followed this https://www.marinepartsexpress.com/engine_flush.html

Imo specifically for VP 280: Hose Engine flush > Bucket > muffs.

Some outdrives have impellers in the leg; for those you HAVE to use muffs/bucket.

 

[skipjack]

Yes,you do have to plug that front water intake hole While flushing a 280 O/D.

 

[fv_ghostdog]

i essentially followed this https://www.marinepartsexpress.com/engine_flush.html

Imo specifically for VP 280: Hose Engine flush > Bucket > muffs.

Some outdrives have impellers in the leg; for those you HAVE to use muffs/bucket.

I will try that thank you for the info!

 

[fv_ghostdog]

Yes,you do have to plug that front water intake hole While flushing a 280 O/D.

What do you use to plug it?

 

[notanotherproject]

Any official name of that Water port hole? And any other recommendations on what to use to plug it? Thanks.

Yes, get a big tote and drop your outdrive in it. Throw the hose in the tote. You’ll know if your water flow can’t keep up with your pump and the hole is no longer a problem….and you’ll never accidentally turn your water on the muffs without the pump spinning and flood your cylinders. I use a husky tote that’s maybe 30 gallons and drop the outdrive down in it empty. Works great too cause you can throw a capful of salt away in the tote water while it runs

 

[slater]

I am actually not too sure. The previous owner passed away and it was his kids who sold me the boat and didn't know much. From the paperwork it seems he repowered in 2019 to a new motor. I'm guessing the risers are same year.

Ive seen alot of boat owners cut corners, new engine & they slap-on the original manifolds...
Their mind-set is I just paid $5k+ for a new eng, cant afford to spend $2k on exh manifolds, ill be fine.....
If you have proper waterflow & risers are hot along with exh manifolds, chances are the exh manifold water passages are blocked internally.
The rust & build-up shrinks the cooling passages overtime & require replacing.
Old exh manifolds is the #1 cause of engine failures on i/o's...
Both risers & exh manifolds should be cool to the touch while running engine at normal operating temp.

 

[fv_ghostdog]

Ive seen alot of boat owners cut corners, new engine & they slap-on the original manifolds...
Their mind-set is I just paid $5k+ for a new eng, cant afford to spend $2k on exh manifolds, ill be fine.....
If you have proper waterflow & risers are hot along with exh manifolds, chances are the exh manifold water passages are blocked internally.
The rust & build-up shrinks the cooling passages overtime & require replacing.
Old exh manifolds is the #1 cause of engine failures on i/o's...
Both risers & exh manifolds should be cool to the touch while running engine at normal operating temp.

Thanks for the info. Going to plug the hole tomorrow and check temp. I'll take it out Saturday on the water and compare as well. If it's giving me high Temps I'll consider replacing. Is there a temperature range that I should be aiming to stay at or under? What would be an alarming temperature for the risers ?

 

[bob_marlin]

my mechanic said the risers should be a MAX of 130

After I had mined replaced, I did a run out 5 miles off Pt Loma and then back to the Coronado bridge I checked them and they were 118 to 120 on the risers

in the front yard on a hose and running for 12 minutes at 1200 RPM they were 110 and 111

 

[fv_ghostdog]

my mechanic said the risers should be a MAX of 130

After I had mined replaced, I did a run out 5 miles off Pt Loma and then back to the Coronado bridge I checked them and they were 118 to 120 on the risers

in the front yard on a hose and running for 12 minutes at 1200 RPM they were 110 and 111

Very helpful thanks so much! I'll report back after I test tomorrow and Saturday.

I did a quick check on trying to plug the hole today - a sharpie marker does fit pretty well. Going to try that in the driveway.

 

[notanotherproject]

Thanks for the info. Going to plug the hole tomorrow and check temp. I'll take it out Saturday on the water and compare as well. If it's giving me high Temps I'll consider replacing. Is there a temperature range that I should be aiming to stay at or under? What would be an alarming temperature for the risers ?

Cant keep your hand on it would qualify.

 

[skipjack]

I used a plastic tapered tip for a tube of sealant.
Before that,I used a bolt with tape on it.

 

[fv_ghostdog]

UPDATE

Ran a temp gun and below are my readings. Also a sharpie marker does plug perfectly.

I was only really paying attention to the starboard side. It wasnt until after 10min I thought to check the other side.

STARBOARD TEMP BEFORE STARTING
Exhaust Manifold: 75
Riser: 75 F

STARBOARD TEMP AFTER 5 MIN
Exhaust Manifold: 151
Riser: 134

STARBOARD TEMP AFTER 10MIN (THERMOSTAT OPENED)
Exhaust Manifold: 139
Riser: 144

PORT TEMP AFTER 10MIN
Exhaust Manifold: 120
Riser: 102 (big diff. from Starboard)

STARBOARD TEMP AFTER 12 MIN
Exhaust Manifold: 135
Riser: 142

Any thoughts on the huge difference between the port and starboard side at 10min?

Should I be concerned with starboard side Exhaust Manifold and Riser at those Temps for starboard?

Would a sea trial give me more accuracy? It just seems like to big of a different between the two sides. I appreciate any feedback.

 

[SilentViper]

Can't say i've ever seen a 10 degree difference in my risers. Nor can i recall ever getting them to 150 without there being a problem. 150 is burn my hand territory; that's how i know it's not working.

since the mainfolds are of dubious age and condition; I'd suggest buying some new gaskets for the elbows; then drain the manifolds and pull the elbows off and inspect the water jackets. if jackets are fine; scrape gasket off mating surfaces, and install with new gaskets. torque bolts down to spec. dont snug them. the gasket compresses over time if you dont and you will spring a leak into the exhaust flow and you'll hydrolock. ask me how i know.

 

[fv_ghostdog]

Can't say i've ever seen a 10 degree difference in my risers. Nor can i recall ever getting them to 150 without there being a problem. 150 is burn my hand territory; that's how i know it's not working.

since the mainfolds are of dubious age and condition; I'd suggest buying some new gaskets for the elbows; then drain the manifolds and pull the elbows off and inspect the water jackets. if jackets are fine; scrape gasket off mating surfaces, and install with new gaskets. torque bolts down to spec. dont snug them. the gasket compresses over time if you dont and you will spring a leak into the exhaust flow and you'll hydrolock. ask me how i know.

Thanks. Going to launch the boat Saturday in the water and just idle it at the dock to see what Temps I get. I know there has got to be a problem but want to see how significant the temp difference will be in water. I'll most likely be pulling the Risers and Manifold this weekend too. B.O.A.T. :/

 

[notanotherproject]

I pulled both of mine last year, taped off the mounting surfaces, filled with concentrated vinegar overnight …man they bubbled like crazy. Got a lot of rust out then blasted the passages with the 0 degree on the pressure washer and blasted a ton more crap out. The material between the exhaust path and water jacket was still easily 1/4”. I’ve been running for the past year, using salt away after use and they’ve been cool to the touch. Good flow. Decked the mating surfaces with a good flat file and new gasket and bolted back together.

 

[fv_ghostdog]

UPDATE

Ran the boat in the big pond yesterday and got exceptionally good numbers.

After five min of running at the dock both sides were between 75 to 85 at the risers and exhaust manifolds.

10 minutes thermostat opened and was between 85 to 95 degrees.

Took it out to open it up and got up to about 3000 rpm and only got up to about 102 on both sides.

Ran the boat in total for 75 minutes. I think my risers and exhaust manifolds are okay and the problem was running on the muffs. In any case. I am going to run the boat the rest of the year and just monitor closely. After the year turns, I may pull the risers and exhaust manifolds and replace them all just for peace of mind. Runs about 700 in parts for all of it.

Previous owner passed in 2019 after he repowered. It sat for 3 years. I believe he took care of the boat, but also, unsure if he was consistent about running salt away and flushing motors. If he didn't, it's possible the boat sat for 3 years and may have corroded slightly on the inside. I will change both sets late winter to be sure. There's only 70 hours on the new motor so I don't want to risk it. For now I think I'll be okay.

New problem arrived though. I'm now leaking at the raw water pump. Buddy told me I need to change the bearing behind the impeller. Is this correct? I just changed impeller only and seems to not have leaked when running on muffs. But he said the bearing may need changing or possibly the whole pump. I don't have a lot of hand room.

Also, any recommendations on marine batteries ?

Thanks all!

 

[skipjack]

I usually replace the whole raw water pump every 3-4 years, I replace the impeller every year.

 

[fv_ghostdog]

yeah i may just do it. When you buy the raw water pump does it usually come with an impeller installed?