Overheating at 30mph

[Galvez83]

Folk i need to pick your brain, i took the boat out today and at idle up to about 15mph temp stays at 160. I went to 30mph and temp spiked and alarm went off. Boat is a 5.7 Penta. I had replaced the impeller a couple of months ago. Risers and one manifold is new. Any ideas what could cause this issue.

 

[Lou C]

Might need to replace the other manifold water takes the path of least resistance

 

[Scott Danforth]

Make sure the water inlet casting is intact. Those white metal wonders last 2 years max

 

[Galvez83]

Make sure the water inlet casting is intact. Those white metal wonders last 2 years max

You mean the one that crosses over from outer transom to the back of the engine? I backflushed the engine and water flows out without any issue.

 

[Scott Danforth]

The one on the drive the hose to the transom shield is connected to

 

[Galvez83]

This is the one i have. I backflushed it and it did not show a restriction but will double check.

 

[Scott Danforth]

the one on the drive, not the transom shield

Item 96 on the old AQ series.

item #9 on DPS.

 

[Galvez83]

Got it, i will replace the part.

 

[Scott Danforth]

inspect it first.

 

[Bt Doctur]

Have you checked the flush port making sure the cap is tight? You could be sucking in air

 

[Galvez83]

Have you checked the flush port making sure the cap is tight? You could be sucking in air

I don't have a flush port on my engine

 

[QBhoy]

Hi. What made you replace the riser and manifold in the first place ? Just in case we are missing something? Did you put the right gasket in between the riser and manifold ? There are variations on water flow set ups, between raw and closed cooling usually.

 

[Galvez83]

Hi. What made you replace the riser and manifold in the first place ? Just in case we are missing something? Did you put the right gasket in between the riser and manifold ? There are variations on water flow set ups, between raw and closed cooling usually.

I bought the engine that was a paperweight. Engine was rusted bad as well as the outside components. The risers and manifolds where full of rust and as a security i went ahead and replaced. The gaskets where bought according to volvo penta parts search engine. They are the metal fiber composite not the plastic ones that came with the Barr risers. Gaskets have the same dimensions as the manifold and riser holes. Here is everything that was changed in the water circulation area.

Impeller
Circulation pump
Thermostat (160)
Thermostat housing and gasket
Hoses from thermostat housing to manifolds
rubber components in outdrive (split outdrive in half and changed)
Temp sensor

Engine overheats at high rpms, the moment i reduce speed to about 15mph the temp slowly drops. At the time of testing i got it to 30mph when the alarm went off. I turned the engine off when the alarm went off. Waited 5 minutes and started the engine. At start up i felt around with my hand and it was indeed hot to the touch. I also squeezed the hoses going from the thermostat housing to the manifolds and they didn't feel like water was flowing. While at idle and someone at the helm i felt around and felt water moving inside the hoses and the temperature change (by feel) it wasn't that hot to the touch.

 

[Lou C]

Remember if you had rusted up exhaust components unless you flow tested them off the engine with a hose and verified that they flow the same; you should have replaced both manifolds. If the one you didn’t replace is partly clogged most of the water will go out the other side and the clogged side will get hot. Get an IR Temp gun & take readings of both sides that will tell you what’s up without taking it all apart.
My engine has Volvo exhaust and @ idle the manifolds & elbows are at 100*; the hottest they get is 135* after coming off plane. If the engine was very rusted the block & heads could be clogged with rust and may need to be flushed out with the front circulation pump & drain plugs removed. This is why I fill mine up with the best AF I can get for winter storage; it reduces internal corrosion. I really haven’t had overheating problems over the years following that plan. Engine runs at 160-175 and it only hits 175 after coming off plane.

 

[QBhoy]

I bought the engine that was a paperweight. Engine was rusted bad as well as the outside components. The risers and manifolds where full of rust and as a security i went ahead and replaced. The gaskets where bought according to volvo penta parts search engine. They are the metal fiber composite not the plastic ones that came with the Barr risers. Gaskets have the same dimensions as the manifold and riser holes. Here is everything that was changed in the water circulation area.

Impeller
Circulation pump
Thermostat (160)
Thermostat housing and gasket
Hoses from thermostat housing to manifolds
rubber components in outdrive (split outdrive in half and changed)
Temp sensor

Did it over heat before all the new parts ?

 

[Galvez83]

Remember if you had rusted up exhaust components unless you flow tested them off the engine with a hose and verified that they flow the same; you should have replaced both manifolds. If the one you didn’t replace is partly clogged most of the water will go out the other side and the clogged side will get hot. Get an IR Temp gun & take readings of both sides that will tell you what’s up without taking it all apart.
My engine has Volvo exhaust and @ idle the manifolds & elbows are at 100*; the hottest they get is 135* after coming off plane. If the engine was very rusted the block & heads could be clogged with rust and may need to be flushed out with the front circulation pump & drain plugs removed. This is why I fill mine up with the best AF I can get for winter storage; it reduces internal corrosion. I really haven’t had overheating problems over the years following that plan. Engine runs at 160-175 and it only hits 175 after coming off plane.

Will double check in the water. Either way that manifold is meant to be replaced. I only changed one because a clear water test was showing me more water flow to one side vs the other. After replacement the issue remained the same. That test was done on a water hose, not at sea. The old manifold remained at the original place on left of engine and it was flowing better than the new manifold. But that could have been trailer unbalance. At sea both where flowing without air bubbles at idle or slow speeds. Clear hoses where removed before yesterday's sea trial.

 

[Galvez83]

Did it over heat before all the new parts ?

new parts installed upon engine rebuilt, can't really compare to any prior usage.

 

[Galvez83]

This is leading me to believe that it might be air intrusion into the system. Regardless i will double check everything from A to Z to confirm. The manifold will still be replaced to match the other manifold from Barr.

 

[QBhoy]

This is leading me to believe that it might be air intrusion into the system. Regardless i will double check everything from A to Z to confirm. The manifold will still be replaced to match the other manifold from Barr.

If it is…an odds on favourite would be the cooler on the suction side of the raw water pump. Between the inner transom and the pump, some set ups have a cooler in line there. Not un common for air to be drawn there, but anytime I’ve seen it, it usually doesn’t prime at all

 

[Lou C]

Might want to flush the block you never know what you’ll find with raw water cooled engines used in salt water. When I replaced the heads a few years ago I could see the block cooling passages were rusty with surface rust but not clogged .