'88 Doral Grande 4.3 v6 OMC Drive one hot manifold?

I just bought a '88 doral grande 21' it has a OMC drive and a 4.3 v6 motor made by gm. I bought the boat as a "turn key" boat...i knew there would be a few problems with it but nothing like this... First off my temperature gauge isn't working properly. Some times it does and some times it doesn't, and other times it seems to fluctuate (increase in temp. with more throttle then drops back to 0). other then a few switches need to be played with to get all my lights to work, the boat is great. This "over heating" is coming from the manifold? or riser being plugged up. Now having said that, the boat ran a few times hard and got hot. i stopped the boat after i noticed a little haze coming from the side storage pockets. Tipped back the engine bonnet and the right side (looking at the motor) was smoking some, and was hot to touch. after a little bit i started it up again, and it ran just fine with the rpm staying low like 1500. the manifolds were both cool enough to hold your hand to it. i assumed that maybe that it was a plugged up and might of blown its self out seeing how the boat was sitting for a couple years. every time the boat starts up and runs just beautifully, its quiet and just purrs. does my diagnostics about having a plugged manifold or riser?
any help is appretiated.
happy boating

You need to do a few things first before pulling the riser.

You need to know if you got good water to the motor.

See the long hose that is coming in from the transom, pull it off where ever it stops say the t-stat.

Drive submerged start the motor and hold the hose straight up have 8-12 inch's of good water ?

Do this for only 3- 5 seconds and shut off the motor.

If good water to the t-stat then open the t-stat cover and see if the t-stat is still good.

Or replace it or take it out all together till you get the temp problem sorted out.

Then it's time to pull the risers " not a bad idea anyway " To check the flappers. Me i'm betting it is the risers maybe both sides and the flappers maybe fell down only you will know when you pull them.

Now say no good water to the t-stat then the hose can be kinked at the inner transom or the fitting that enters the transom could be clogged on the outside.

Or the impeller in the drive is shot.

Post back what you find and we will go from there.

the impeller in the drive needs to be changed every few years - sounds like yours needs changing. with a used boat, it's always a good idea to change it pre-launch because you don't know how old it is

as far as i know this motor doesn't have a riser. it was the "older piss poor design" says a mechanic from the local parts store. The manifold is one peice which slopes from front to back and makes a turn down into a double a joining rubber hose clamped on boot. make any sence?
Myles
Happy Boating

yes i know. batwing mani's with the riser built in. If the riser or mani's go you can install a center mani and riser setup and toss them bats in the garbage.

Sounds like your there now.

The bat wings are not bad but they can clog, what you have to do it slide down the lower rubber exhaust hoses, then loosen the 4 nuts that hold them on and they will come right off. Spray some silicone spray on the Y pipe to make it easier to slide down the rubber hoses. Take off the manifolds, look in the ex ports for rust, and in the ex ports on the engine as well. If it's not rusty in there, then look at the outlet. There will be 4 water outlets, one or more could be clogged. You can unclog em with a small screwdriver blade, then hook up a water hose to the water inlet and flush em out. If this is a freshwater boat I'd say clean em out and re-use ,if a brackish or salt boat then there is a conversion using Osco risers and manifolds that will replace the bat wings. I just replaced mine, after 5.5 seasons in salt one outlet was clogging, but other than that, they are re-usable. The batwings had one big advantage, no riser/manifold joint to leak, that's why Mercru went to the dry joint manifold design, the riser/mani joint is the Achilles heel of I/O cooling systems.

got any of these conversion kits for sale any one? So far the boat has been sitting at the dock, been way to busy to try anything just yet, but ill get to it and definitely let you know what i find and maybe some pics to go with it. Thanks for the help and information guys.
Happy Boating

you're going to replace $1000 worth of manifolds before the impeller?

I had the same problem. I just pulled the manifolds and drilled out the crud that was built up in the outlets of the risers and they work fine now. The thing I like about the bat wings is they are so compact, making it much easier to work around the engine.

What can happen is a internal crack into the ex. passage from the water passage. Then you can get reversion. What you can do is pressure test the whole shebang.

I wish you luck with the one piece that you cleaned out.

I tried to save a riser just a few weeks ago on my boat.

Motor overheated on the first trip out on the boat with my wife and son, melted the rubber hose right off and spewed sea water all over the motor, i limped back in but now it's running fine.

Really was my fault is was 6 years when i put the last riser on.

I just pulled the impeller off the boat and it looks to be in good shape. All the parts are shiny and the rubber impeller its self is in good shape. No pieces hanging off or missing. So the next step i took was to remove the manifolds and lone behold they are both pretty plugged. one is still flowing a little water through it but not a whole lot. The other side is the one that was heating up and its getting only enough water to make a little steam. thats it. so now i am on the hunt for new/ used manifolds that are in good shape till i can save my pennies to buy the proper conversion kit (the two piece manifold). Anyone have any of these kicking around that they would like to part with?
Thanks, Myles.
Happy Boating

Does silence mean that nobody has any they want to part with?

we're pretty much a bunch of fishermen and DIYers.... you can buy new manifolds from the host of this board, marineengine.com, or just google up OSCO omc conversion