4.3L 431B overheating

Well, the outdrive is back and all good.

Engine overheats now!

Checked impeller. It was worn so I replaced it. NO broken or lost rubber blades.
Checked thermostat. It opened and closed with heat an cold.
Checked raw water intake on out drive. Removed hose at water neck. Applied water via muffs, water came out neck housing.
Checked circulating pump V-belt. Tight.

NO water exits rear of the boat at all. When I first started it, some pink glycol came out (from winterization). Now NONE.

Thoughts?
I had a similar problem in 2011 and it was the circulating pump.

Tom

The best I can offer you would be to study and learn the seawater path for your cooling system.

The smallest suction breach can play hell with the seawater pump's ability to pull water in.

A replacement impeller should sit proud of the pump body by approx .010" or so. Wrong impeller can prevent suction.

The seawater pump inlet/outlet are directional. Swapped hoses will prevent the seawater pump from working.

Previous impeller damage might have left impeller vane fragments some where in the system. If so, you will want to find and retrieve them.

The 431B is raw water cooled. However, if it has been fitted with a closed cooling system, check the seawater side of the Heat Exchanger.
The tube bundle may be blocked by debris.

If raw water cooled, pull the T-stat housing and examine it.
Also look at the fittings that direct the seawater into the manifolds.

Between the manifolds and elbows, you will have seawater transfer ports.
Make sure that these transfer ports are clear and open.


The 431B is an AQ series.
Make sure that your exhaust couplers (the coupling hoses) are not being clamped over the elbow's scalloped areas.

If the couplers are clamped and are squeezed into the scallops, they may be restricting the seawater that wants to exist the elbow's mixing chamber and on out the exhaust.



By the way, the OEM elbow to Y-pipe couplers are always too short.
If you replace them, purchase two lengths of 95mm soft wall Marine exhaust hose and by the foot.
Make sure that they are about 2" longer than the OEM so that you can avoid clamping them over the scalloped areas.
NOTE: this is a 95mm soft wall marine exhaust hose.... not 4".
Also, being soft wall, there is No wire re-enforcement in this hose.




Do your forensic work, and you'll find the problem.



.

Well, as they say, when something doesn't seem right....

All fixed. I had the incorrect water neck and it was sucking air. Had picked up a plastic one with an oval hose hook up. Got a metallic with the round hose hook up and all is well now. Live and learn!

Tom