I have purchased a set of Eddie Marine EMI Thunder manifolds that i have installed on a pair of 496 ho's and have had numerrous overheating problems at the exhaust that is resulting in setting off the alarm sensors at the manifolds. I have not had any engine overheating and have checked the water pressure coming in and it is the correct flow. However the flow of water through the manifolds is not the same as the stock exhaust. I was wondering if anyone out there is having similar problems or if anybody had a little advise. No one at Eddie Marine can seem to come up with a solution.

I am having the same problem but only left manifold on port engine. It got up to 180 while the other 3 were between 118 to 123. My raw water pump was grooved up pretty bad so im going to change it and see what happens. Pump should be in tommorow. Alot of guys i know have had to change the raw water pump on these 496s because they were grooved on the housing sides. If this fixes mine im going to order a new one for the stbd. engine. How many hours on your motors? Ive got 81 on mine.

i have about 35 hours on both engines and all four manifolds are heating up. they are in a 32 sunsation dominator 2006 model. i changed to the ho's from the 496 mag just after i purchased the boat

What is your water pressure at? mine is 17-18 on the port eng. and 22-23 on the stbd. Thats at 3800 rpm. That was the same with the stock manifolds so the mechanic and i figured it wasnt the problem. He called Mercury and they said to change the pump.

I ran into the same thing on my Gils, what I found was the fitting going into the risers which are the aluminum ones was screwing in to deep cutting the flow way down. I cut about 1/4" off the end flows like crazy now problem gone!
Phil