I had an interesting conversation with an engineer which worked for Mercruiser back in the 90's. I discussed with him exhaust manifold replacement. He said in the 90's Mercruiser worked on an electrodeposition coating for the internal and external surfaces on their manifolds and risers. Mercruiser would then paint over the coating for appearance. In a nut shell it extended manifold life dramatically possibly to lifetime. He believed the thermostat housing and heads started getting the coatings the early 2000's. He said manifolds failure now occur because of cracking vs. corrosion. Cracking is caused by fastener location, vibration, and sediment build up creating hot spots. Most Mercruisers engines are GM engines, the manifolds on an marine engine are much heavier than on a car engine, this leads to stress around the mounting holes.
I discussed the cost of the new catalyst manifolds and he indicated they should never need replaced due to the coating. He said if you are not seeing rust stains or discoloration the manifolds are not deteriorating. I know exactly what he is talking about. I drained my engine block to prevent freezing and a huge puddle was left on the concrete. I thought for sure there would be a huge rust stain once it evaporated, there was none just some sediment. If you start seeing rust stains you are back to a 5 year expected life.
The kicker is aftermarket manifold manufactures OSCO, BARR do not use the coating and I know the rust he is talking about. I actually would flush my engine in front of my house so I wouldn't get rust stain on the driveway on my other boat.
My buddy had a 350MAG where the manifolds failed due to cracking. I busted them apart and was shocked to find no rust. They had cracked in one of the corners due to sediment. The new catalyst manifolds are much smoother almost a pipe in a pipe this should reduce the ability for the sediment to accumulate.
He did saying flushing is very important. He estimated you get about 70% of the "salt" out. the other 30% gets attached due to its tenacious bounding properties. Once it solidifies it is there to stay. To guarantee no crystallation maintain cooling temps below 140F. Funny he said that because that is what my thermostat was in my last boat which lasted in excess of 30 years. He said they are now running 160F and would recommend 140F but the engine needs to be designed with the proper clearances to run 140F to prevent excessive engine wear (hot piston, cold cylinder). He said very rare for an engine to ever corrode through since the temps are low, in the manifold however run much hotter.
So in a nutshell the old philosophy of changing manifolds every 4-6 years is not applicable to any Mercruiser engine built after 2000 unless cracking occurs which usually leads to an external leak.
Let the flames begin....
I discussed the cost of the new catalyst manifolds and he indicated they should never need replaced due to the coating. He said if you are not seeing rust stains or discoloration the manifolds are not deteriorating. I know exactly what he is talking about. I drained my engine block to prevent freezing and a huge puddle was left on the concrete. I thought for sure there would be a huge rust stain once it evaporated, there was none just some sediment. If you start seeing rust stains you are back to a 5 year expected life.
The kicker is aftermarket manifold manufactures OSCO, BARR do not use the coating and I know the rust he is talking about. I actually would flush my engine in front of my house so I wouldn't get rust stain on the driveway on my other boat.
My buddy had a 350MAG where the manifolds failed due to cracking. I busted them apart and was shocked to find no rust. They had cracked in one of the corners due to sediment. The new catalyst manifolds are much smoother almost a pipe in a pipe this should reduce the ability for the sediment to accumulate.
He did saying flushing is very important. He estimated you get about 70% of the "salt" out. the other 30% gets attached due to its tenacious bounding properties. Once it solidifies it is there to stay. To guarantee no crystallation maintain cooling temps below 140F. Funny he said that because that is what my thermostat was in my last boat which lasted in excess of 30 years. He said they are now running 160F and would recommend 140F but the engine needs to be designed with the proper clearances to run 140F to prevent excessive engine wear (hot piston, cold cylinder). He said very rare for an engine to ever corrode through since the temps are low, in the manifold however run much hotter.
So in a nutshell the old philosophy of changing manifolds every 4-6 years is not applicable to any Mercruiser engine built after 2000 unless cracking occurs which usually leads to an external leak.
Let the flames begin....
… and they still do today
