Ford Mercruiser 188 Rehab and Cooling

[IslandExplorer]

Hello, I have a 1974 Mercruiser 188 / Ford 302 2V V8 with 888 (MC1 outdrive) that I have been working on. After pulling it from the boat for further inspection I have decided that the corroded log manifolds cannot be trusted so they will be replaced with nice new ones. I am working on refurbishing this 302 powerplant despite it being a long gone Merc model, I am aware. Also keeping the MC1. Have a number of questions and looking for some recommendations to help with my plans.
(Also- I appreciate the reasoning but not looking for advice to switch to a newer whole setup. I'm definitely keeping the old Ford 5.0 V8.)

1- I will be converting to a crank driven seawater pump and losing the outdrive pump and small transom water passage. Will be adding a marelon thru hull with valve and probably a strainer and then to sea pump inlet. Will likely switch to an automotive engine circulating pump since it will only be running antifreeze.

Any experiences/recommendations on a good affordable crank pump?

Think the ol outdrive will be cool enough with no water running through it and only 188hp going in? I do plan on doing some long hauls at higher speeds to fishing grounds when conditions are right. Boat is 25 foot, aluminum, with cabin.

2- Looking at new exhaust manifolds. Top choice currently is the Barr Marine FM183 manifolds and Barr 20-0100 4" exhaust risers.

I know the manifolds are typically for inboards but I saw a thread with these used to update a 302 and it looks great. Pretty simple plumbing to reconnect from there to 888 Y pipes.
Although cool- I have no intention of running thru hull exhaust. I want it quiet enough not to wake eveyone in the harbor when idling around. Good to be considerate of ppl still asleep on their boats! Anyhow, these seemed like a really good way to convert to newer style center riser manifolds.

Any thoughts on all this?

3- I have no idea what raw water flow rate I will need for the cooling system yet. I will be cooling the engine and exhaust via a Sen Dure heat exchanger from a 454, it's about 4"x27". I know I am not dealing with a ton of power here but I want the cooling system to be more than capable of keeping everything cool under full load.

Please feel free to tell me what you think! And thanks if you actually read all this.

 

[Scott Danforth]

look at the volvo pumps. they are Johnson pumps.

however you still need to maintain the raw water pump in the drive to keep the drive cool

are you running the heat exchanger as a full system or a half system? that detrermines how you MUST plumb the system.

also, adding a heat exchanger to a used marine motor requires the motor to be torn down and the water jacket to be cleaned. the only two ways to clean the water jacket. fully bake the block, and rebuild the motor, or take a bit of 1/4" steel cable and with the short block on the engine stand without the heads and clean out the block. the heads can not be cleaned out and you should consider getting new heads. failure to do so will plug the heat exchanger as the rust bits will come out of the water jacket.

 

[IslandExplorer]

Thanks for the quick reply Scott, I will be running a full system so that the risers and HX will be the only raw water cooled parts hopefully.

Definitely good to know the drive still needs to be cooled. Was really hoping to lose the drive pump though! Maybe I'll replace it with a drive shower tube..

As for the engine- it may or may not be a marine engine depending on which of 2 302 motors I use. Need to decide which real soon.

The marine engine was raw water cooled and lived part time on a FW river. It definitely looked pretty crusty in the cooling passages down low in the block when I did the freeze plugs. Had leaky steel ones before. Otherwise it looks great internally (on oil side) and super clean like it had a nice rebuild with fresh pistons, oil pump, etc and low hrs since bc of how tight the pistons and whatnot are. It sounded great running too which was encouraging.

This is why I'm considering doing a better partial cleaning of the block, wire it out, flush it really good with a pump, and run it with a nice inline coolant filter screen like the ppl I read about that did something similar. Craziness??

The other engine is from a 96 Bronco and has clean passages which is great but does not have 351 heads, or the proper cam, or the right flywheel, or balancer, or any of that stuff. It is a roller motor and does have great heads for low rpm efficiency and low tension rings..
I can't swing a whole new engine/rebuild in addition to everything else unfortunately so will need to pick one somewhat as is block or the other.

 

[Scott Danforth]

Drive shower won't keep the lower unit shaft seal cool.

 

[IslandExplorer]

Good point, I'll definitely need to keep the pump in there then. I already have a new one anyway. Too bad those pumps don't put out more flow bc it would be nice to use it for the heat exchanger and be done.

If I kept the pump but removed the hose by the bellows and sealed the transom pass thru would that still cool the drive ok? Assuming it would just dump water out the outdrive housing harmlessly?

 

[IslandExplorer]

Also, after thinking about it more, I am leaning toward not using the X raw water block. Like you said, without proper tear down and rebuild I just can't clean it that well.

 

[Scott Danforth]

you can always follow what mercruiser suggests regarding plumbing on a full system heat exchanger

me personally, I would put a new long block in front of the heat exchanger.

 

[IslandExplorer]

I wasn't able to find an 888 full cooling sytem setup example from Mercruiser. This model seems like it wasn't as common so maybe there wasn't a factory full system setup, I don't know. Since the parts are rare if not non existant anyway- I am fine with doing a non standard setup/ copying another converted full sytem that works.

I'm guessing the engine coolant goes through the block first, circulates until temp is reached, and then it starts flowing through the exhaust manifolds, then the exchanger, then back to pump.

 

[IslandExplorer]

The system I read about that sounded the most like mine had the engine coolant controlled by the thermostat with a small bypass passage to keep coolant flowing through the exhaust a little even when thermostat is closed fully/still warming up. Going to have to find one like that probably.

The capt said the housing was a simple automotive type, not a 6+ port block like Mercruiser used with the old raw water system. It was on a 302 inboard running what looked like a pretty simple plumbing setup. Here is a pic of it below.

This seems like a really nice setup and they reported even cooling and reliable results. Notice the in line coolant fill ports. Those have screens in them to catch random debris from an old block. I like the simplicity of it, looks more streamlined than factory too.

See anything wrong with running something like this on my 888?

Has anyone on here had a system like this on a Ford small bock and knows a good thermostat housing to use?

 

[Scott Danforth]

be carefull. as the heat exchanger from the big block may have been set up for a half system or a full system.

you need to plumb per the heat exchanger design. dont go mixing and matching parts randomly. how many ports on the heat exchanger glygol side? how many on the raw water side? post a pic

half system should be a 1-1/4 raw water inlet, two 3/4" raw water outlets and at a minimum 1 1-1/2" glycol inlet, 1 1-1/2" glycol outlet, 1 1" fill line port, 1-2 vent ports. this will use a standard automotive style thermostat water neck

full system design will be dependent on thermostat location, if its on the manifold, there will be 1 large glycol outlet, 4 to 6 glycol inlets. if its in the plumbing, there will be at least a thermostat mount on the heat exchanger

mercruiser used the in-leg pump for half-systems, and then used a y-fitting and a crank mounted pump with its own pickup as supliment on the full systems on the GM motors. they really didnt do much on the ford motors

 

[IslandExplorer]

It is a really simple looking exchanger, much like the San Juan units I've seen. Has only 4 ports other than 2 small threaded drain or vent holes, 2 coolant, 2 raw water. It's supposed to be a triple pass I think. Made by Sen-Dure.

 

[IslandExplorer]

Interesting that they used a Y pipe on those systems you mentioned. Was that for convenience or is there an advantage vs just 1 larger seawater pump?

 

[Scott Danforth]

its a 3 pass for a half system, not the 5-1/2 pass used on full systems. it also does not have the expansion/fill tank that you will need. Not the puke/overflow tank