Hybrid RWC FWC idea.

[joe_db]

Some of you may recall I was not happy with my engine temps with FWC and the related effect of heating the boat up and heating the fuel pumps and filter up too.
I replumbed for RWC for a bit and confirmed the engine cools fine with the original setup. Actually now it has been cleaned and some 1/2" hose replaced by 5/8", I cannot get to 120 degrees running flat out for an hour.
I checked out a few powerboats being worked on at the local shop and found something interesting that gave me an idea - many of the FWC V8 engines do NOT run fresh water through the manifolds. Raw water goes through the heat exchanger, through the manifolds, and out the exhaust. I am going to replumb that way, fresh water through the block and raw water from the HX, through the manifold, and out the exhaust. My thinking is the manifold will be quite a bit colder and the total heat handled by the exchanger quite a bit less. I am hoping it will be cool enough to hold 160 or 140 degrees depending on what thermostat I put in. Downside of course is the manifold won't last forever with salt water in it.

[Dave Neptune]

Joe, your pretty much spot on. Just don't forget that the manifold won't live as long. And since I have seen many RWC engines with 20 plus year old manifolds it should not be a big deal.

Dave Neptune

[joe_db]

$300 or so for an A4 manifold beats around $1,000- $2,000 for a set for a V8!

[Dave Neptune]

Indeed, that's hitting the nail on the head and not the one on your thumb.

I would not hesitate. I was thinking of the same thing however I sold the boat and A-4 before converting to FWC.

Dave Neptune

[Solana]

Thank you for mentioning this. I was recently contemplating the same thing. I'm adding FWC so that I can have hot water on the boat. I had decided that the recommended routing of the FWC through the manifold would be good in that it would give me higher coolant temps for better heating of the hot water tank. I had not considered that the FWC heat exchanger might be unable to remove enough heat to regulate the engine temperature. Eliminating the thermal load from the manifold on the heat exchanger would certainly improve its ability to regulate the engine temp.

[joe_db]

So far I have got good results. The raw water temp is dropping by the day, but it looks like I could run as cold or close to it as with RWC.
I'll have to add the thermostat back now and see how that does.
Maybe we need an electric FWC FAQ?

[Tim]

Joe, are you still running raw water through the manifold ? If so, how is it working out? I added electric fwc last year. I think the used heat exchanger i am using is a little under sized and running raw water through the manifold may take enough load off of the heat exchanger to reduce engine temps.

[joe_db]

I am and it works. I can run pretty hard and the coolant temp will be about 160 degrees or so.

Joe, are you still running raw water through the manifold ? If so, how is it working out? I added electric fwc last year. I think the used heat exchanger i am using is a little under sized and running raw water through the manifold may take enough load off of the heat exchanger to reduce engine temps.

[Tim]

I tried plumbing the raw through the manifold and it made very little difference. Temp still goes over 200 at half throttle. I think that the Sendure heat exchanger I have is under sized for the flow produced by the Johnson pump. I switched back to raw water cooling and temps are back to around 130 at half throttle and rising toward 150 at full throttle.
I haven't given up on the electric FWC, I'm just putting it on hold until I can get the right heat exchanger.

[joe_db]

Can we get a photo/description of the HX? Is it smaller than the Moyer/Indigo version?
Are you running a ballast resistor?

I tried plumbing the raw through the manifold and it made very little difference. Temp still goes over 200 at half throttle. I think that the Sendure heat exchanger I have is under sized for the flow produced by the Johnson pump. I switched back to raw water cooling and temps are back to around 130 at half throttle and rising toward 150 at full throttle.
I haven't given up on the electric FWC, I'm just putting it on hold until I can get the right heat exchanger.

[Tim]

It appears to be smaller than the Moyer/Indigo heat exchangers. I don't know the dimensions of the Moyer heat exchangers. Here is a photo of the Sendure mounted to the manifold. And yes, I do have a ballast resistor on the pump, Tom Stevens installed the resistor before I picked it up.

[ndutton]

We have seen that HX on other A-4's without issue. When you converted to electric FWC did you take other measures such as:

• Enlarge the sideplate Tee and diverter cap?
• Physically muck out the water jacket around the cylinders?
• Add the bypass valve?
• Remove the thermostat?
• Thoroughly clean out the used HX?

[joe_db]

I dropped about 15 degrees by bypassing my ballast resistor, FYI. I would measure the pump voltage and see what you have. I can also lose 10 more by running the second pump that still has the resistor. I am thinking about getting 0.5 ohms for both, my 1 ohm was too much.
Also note no law against two heat exchangers, you can keep that one and add another If you do, run the raw water the opposite way as the coolant, i.e. coolant goes second into the one that gets raw water first

[Tim]

I'm picking up the oil filter system from Indigo tomorrow, I'll ask him about the heat exchanger capacity with electric pump while I'm there.

Neil, the engine was just rebuilt and the cooling passages were cleaned as was the heat exchanger. The cooling jacket inlet was enlarged, but I did leave the thermostat in place. I was hoping that taking some of the load off of the heat exchanger by running raw water through the manifold would help, but engine temp still got up near 230 at 3/4 throttle. If the engine temp. was just a little too high, then I would be willing to fiddle with the flow to try and make it better. But since the temp is way too high even with fairly cool raw water, I decided to revert back to raw water cooling for now.

[joe_db]

Your very high temps sound like an airlock. It is WAY harder to get the air out of the system with an electric pump than you would think. It took me several tries.