7.4 mpi port side is almost too hot to keep your hand on

dinopaul

Member
Jul 11, 2011
32
france
Boat Info
330 Sundancer 1998
Engines
twin 7.4 mercruiser
hi,
during an outing, one of my engines started to smoke (white smoke) the engine temperature was at 170.
I thought of a head gasket and when I got back I checked the oil and it was clean, I took the compression and all 8 cylinders are at 120-125 psi.

on both engines Exhaust, manifold, riser and elbow have 5 years old but only 10 hours in fresh water.

I reversed the riser and the elbow
I inverted the Thermostat HOUSING ASSEMBLY
I changed the raw water pump
I checked the exchangers and the pipes

and still the port side very hot I can not let my hand over.

has anyone encountered this problem?

Thank you all
 
hi,
during an outing, one of my engines started to smoke (white smoke) the engine temperature was at 170.
I thought of a head gasket and when I got back I checked the oil and it was clean, I took the compression and all 8 cylinders are at 120-125 psi.

on both engines Exhaust, manifold, riser and elbow have 5 years old but only 10 hours in fresh water.

I reversed the riser and the elbow
I inverted the Thermostat HOUSING ASSEMBLY
I changed the raw water pump
I checked the exchangers and the pipes

and still the port side very hot I can not let my hand over.

has anyone encountered this problem?

Thank you all
Ya, this summer, mine was a blocked tube from Bravo thru transom. You would think both sides would be very hot, but in my case one side was way hotter than the other. I don’t remember which side.
We changed ‘everything’ before taking to professional shop who pulled the Bravo and found problem. Good luck.
Edit: are you saying port engine or port side of an engine. I have a single.
 
Last edited:
Ya, this summer, mine was a blocked tube from Bravo thru transom. You would think both sides would be very hot, but in my case one side was way hotter than the other. I don’t remember which side.
We changed ‘everything’ before taking to professional shop who pulled the Bravo and found problem. Good luck.
Edit: are you saying port engine or port side of an engine. I have a single.


in line propeller shaft, I have two engines and my problem is on the starboard engine on the port side
 
hi,
during an outing, one of my engines started to smoke (white smoke) the engine temperature was at 170.
I thought of a head gasket and when I got back I checked the oil and it was clean, I took the compression and all 8 cylinders are at 120-125 psi.

on both engines Exhaust, manifold, riser and elbow have 5 years old but only 10 hours in fresh water.

I reversed the riser and the elbow
I inverted the Thermostat HOUSING ASSEMBLY
I changed the raw water pump
I checked the exchangers and the pipes

and still the port side very hot I can not let my hand over.

has anyone encountered this problem?

Thank you all
"White Smoke"?.....or Steam? White smoke is a sign you are burning oil. A certain amount of steam out of the exhaust on the other hand is normal (given the water temperature-dew point etc of your location).
Not sure what you mean by "reversed the riser and elbow" or "inverted the thermostat housing. assembly"? Do you mean you inspected them?

I suspect the water cooling passages on the port side riser/elbow on the stbd motor are clogged, perhaps from internal corrosion blocking the passageways. Easy enough to check by removing them and doing a thorough inspection and as long as you have them off, take a look inside the manifold.

If the exhaust components were "5 years old" in salt water BEFORE 10 hours in fresh water they most likely are due to be replaced, especially if they weren't flushed with fresh water after use.
 
"White Smoke"?.....or Steam? White smoke is a sign you are burning oil. A certain amount of steam out of the exhaust on the other hand is normal (given the water temperature-dew point etc of your location).
Not sure what you mean by "reversed the riser and elbow" or "inverted the thermostat housing. assembly"? Do you mean you inspected them?

I suspect the water cooling passages on the port side riser/elbow on the stbd motor are clogged, perhaps from internal corrosion blocking the passageways. Easy enough to check by removing them and doing a thorough inspection and as long as you have them off, take a look inside the manifold.

If the exhaust components were "5 years old" in salt water BEFORE 10 hours in fresh water they most likely are due to be replaced, especially if they weren't flushed with fresh water after use.
No. White smoke does not indicate burning oil. Blue smoke does.
 
No. White smoke does not indicate burning oil. Blue smoke does.
yup, you are right.....I was trying to point out the difference between actual "smoke"...white/blue etc vs. steam. He didnt say if this "smoke" immediately dissipated (like steam does) or if he was fogging the area with actual smoke.

  • Light or thin white exhaust smoke is typically water vapor
  • Blue/gray exhaust smoke means there's likely an oil leak and engine is burning oil.
  • Black exhaust smoke can appear when the engine is burning too much fuel
 
Last edited:
"White Smoke"?.....or Steam? White smoke is a sign you are burning oil. A certain amount of steam out of the exhaust on the other hand is normal (given the water temperature-dew point etc of your location).
Not sure what you mean by "reversed the riser and elbow" or "inverted the thermostat housing. assembly"? Do you mean you inspected them?

I suspect the water cooling passages on the port side riser/elbow on the stbd motor are clogged, perhaps from internal corrosion blocking the passageways. Easy enough to check by removing them and doing a thorough inspection and as long as you have them off, take a look inside the manifold.

If the exhaust components were "5 years old" in salt water BEFORE 10 hours in fresh water they most likely are due to be replaced, especially if they weren't flushed with fresh water after use.


I removed the two elbow and the two risers they are beautiful, I did not dismantle the manifolds but they are beautiful on the top and the pipes, the boat is still in fresh water.
the smoke is vapor, it arrives after 10 minutes at 800 rpm when elbow becomes very hot +/- 100 ° and when I accelerate to 1200 rpm the smoke disappears and the elbow decreases to 78 ° in 30 seconds.
 
I removed the two elbow and the two risers they are beautiful, I did not dismantle the manifolds but they are beautiful on the top and the pipes, the boat is still in fresh water.
the smoke is vapor, it arrives after 10 minutes at 800 rpm when elbow becomes very hot +/- 100 ° and when I accelerate to 1200 rpm the smoke disappears and the elbow decreases to 78 ° in 30 seconds.
They can look perfect on the outside and still be plugged. Best tool I bought for the boat was a laser thermometer. Is that how your measuring the temps?
 
I removed the two elbow and the two risers they are beautiful, I did not dismantle the manifolds but they are beautiful on the top and the pipes, the boat is still in fresh water.
the smoke is vapor, it arrives after 10 minutes at 800 rpm when elbow becomes very hot +/- 100 ° and when I accelerate to 1200 rpm the smoke disappears and the elbow decreases to 78 ° in 30 seconds.
Is this Fahrenheit or Celsius?
 
Port side will almost always be warmer than strd side as that is the last area to get raw water and by the time it gets there is already quite warm. Therefore will not remove as much heat. You need to know that you are getting ample raw water flow. If you have drives, certainly check for Bravoitis. If not check your flow path - thru hull intake, strainer, pump, heat exchanger. Any restriction with these will cause poor flow and the result will be a hot port exhaust manifold.
Been there, done this. Ours was BravoItis - we elected to block off the drive raw water intakes and install thru hulls. Major difference in water flow and engine temps. Also, removed and cleaned heat exchangers. Flushed the oil, fuel and pwr steering coolers with Barnacle Buster in a loop. Changed impellors. Then finally changed out the exhaust manifolds, which by the way - looked wonderful on the outside. Took them to my very trusted Merc Service Guy and his comment was "you were one cruise away from a disaster", meaning the insides were trashed. So total cooling system R & R and running nice and cool. Best thing is I now know exactly where my cooling system stands. No guessing and crossing fingers that a manifold dosn't collapse and cause hydrolock.
 

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