I have a 305 mercruiser that is overheating. Have changed the manifolds and risers , sea pump t-stat . I ran over some mud 10 years ago and the overheating started. I havn't used the boat since then. This year I flushed the engine out replace those parts and sit still overheated.
If this Engine is truly fitted with a Closed Cooling System, I would need to ask you if the seawater side of the heat exchanger was cleaned after the "mud" incident?
My Mechanic took out the stainless steel restrictor plate in the riser and it still overheated.
Yes...... find another mechanic who understands why the SS restrictor plates were installed in the first place.
Should I be using the restrictor plate in the riser ?
Again.... can you clarify as to the SS restrictor plate being installed underneath a Riser/Spacer or underneath an actual Elbow?
(the two are not the same part)
Mechanic says they are only used in the closed water systems . The restrictor plate originally had a small hole in it and it ran cool years ago befor I had the overheating problems.
I must assume that your system is either an "open" system, or is a "Half Closed Cooling System". (engine only)
When a SS restrictor plate (one with the weep hole) is used, the exhaust manifold is typically supplied with seawater at one end, and will have a seawater exit at the other end. (the seawater transfer ports are NOT used)
The exiting seawater then enters the Elbow via an additional port.
The weep hole in the SS plate is there to allow draining for Winterizing.
Now....... if your exhaust manifolds are equipped with a fitting at one end only..... then the seawater transfer ports must be fully open.
I havnt replaced the water pump yet although I did replace it in 2004 when repowered the boat.
Which pump are you speaking of?
I ask because some call the "Engine Circulating" pump a water pump.
Are you speaking about the "Circ Pump", or the "seawater pump"?
I have twin inboards and the other motor when I took it out 10 years ago didn't overheat at all . It now does over heat and we are going to take the restrictor plates out. This engine's timing is off , can that cause overheating ?
You bet it can...... and it may not stop at that!
Do I need the restrictor plates ?
As said...... if your exhaust manifolds use the seawater transfer ports to supply seawater to the Exhaust Elbows, then NO..... the transfer ports MUST be fully open.
If your exhaust manifolds are fitted with a seawater supply and a seawater outlet that runs to the Elbow, then yes, it is likely that Merc wants the SS restrictor plates installed.
Find your Engine model number and look up your cooling system schematic.