Heater plumbing (Ford 351/GT40)

I didn't want to hijack the 2000 SAN heater thread (as entertaining as it was....). But since that was a GM, I thought better of clouding the issue.

I have a 4-vent heatercraft heater I put in right after we bought the boat new. I have tried numerous plumbing locations, trying for the hottest water possible.

As was posted in the other thread, pulling it off the manifold just before the thermostat is not only the hottest, but it is a 1/2 inch connector vs the 3/8 on the block, so more flow.

I have used the bottom of the elbow below the circulation pump as the return. However, I have had problems with idle heat, so I added a 12 volt in-line hot water circulation pump just before the heater core. That helped, but since I happened to have two of these, I added another one at the return, just before the elbow before the circulation pump. That also helped. However, that pump went out recently, and I decided that rather than a pump sucking at the end of the line, I'd put a new one right after the line coming from the manifold connector so it would push hot water.

The problem I'm having (which I think is the root of all of the so-so performance of the heater) is that because the manifold location is at the top of the engine, that is where any air is, so the air gets up into the heater hose, and then my 12v pump sucks air. I think this is why I have always had some problems with really hot air coming out, except on occasion.

So, anyone have a solution to it? I have not wanted to change the return to the intake side of the raw water pump even though that will solve the problem, simply because that means longer warm up times, and an issue with my shower temp (I use my shower to fill a "hot tub", and bleeding hot water back into the raw water line means more cold water into the engine, making it harder to keep the engine warm when filling the tup).

Granted, I could put a valve on the heater line and shut it off when filling the tub, and if I can't figure out how to get ride of the air bubbles trapped in the hose, I guess I'll have to do that. But I'm looking for any suggestions before I got that route.

And for anyone who has returned to the input side of the RWP, did you notice any difference in engine temp, especially sitting at idle?

Thanks,

For pre-RWP return plumbing Heatercraft sells a Y-pipe adapter (they have a 1" version but I can't find it on the site). The passage on the 5/8 side is only semi-open- probably a 1/8" hole, so you really only get a trickle of flow back into the RWP. The suction of the RWP is enough to keep heat going at idle.

That said, my return line is simply plumbed to the stbd block drain and I get great heat at idle FWIW. That said the EFI motors run a 160 'stat.

Thanks all for the replies. To answer all, I was thinking of making up a T before the RWP (rather than buy the Y from heatercraft/SKIDIM, and then putting a valve on it to shut it off when filling our hot tub. However, as some of you have mentioned, manifold to circulation pump should be good (I've also tried manifold to block but that did not flow as well).

I don't think it is a worn RWP impeller that is starving the engine of water because 1. it has only about 50-75hrs on the latest impeller and this is a problem I've always had without the inline 12v pumps, 2. it sucks and pumps water fine at idle, and 3. even if it was starving water, I would think that it would retain water in the engine (ie: if water isn't flowing into the engine through the thermostat, then water is not leaving the engine for the exhaust manifold) so water would still flow through the heater line (and of course, the engine would overheat which it does not).

So I think my two options at this point are:

1. plumb the return to the input side of the RWP
     + can remove the inline pumps since the vacuum of the RWP should pull water through it quickly
     + vacuum/suction should eliminate any air, so higher water flow which equals higher heater output
     - may slow warm up slightly and cause shower / hot tub water to be cooler if I don't install a valve to stop heater flow during warm up or filling the hot tub

2. plumb from block to circulation pump
     + will eliminate any air trapping due to low location on engine
     - will require inline pumps as that flow is not great (especially with the 3/8 tap on the block
     - water temp will be lower than at the manifold so air not as hot

I liked plumbing from the manifold to the circulation pump with the inline 12v pumps since that was the best of both worlds. But if I keep getting air bubbles at the top of the manifold that then gets into the line, I'm going to continue to have this problem (and even high speed runs don't always blow out the bubbles).

I'm leaning toward option 1 because I want the highest possible temperature out of the heater. One additional concern with that method is what potential issue can a continual stream of cold water entering the engine have? Since it was mentioned that the Y adapter is partially blocked off to restrict the flow, if I make my own with just a T, am I going to have excessive flow that causes cooling issues?

Dang! The way I have it plumbed now is perfect except for those stupid bubbles in the line!!

Gordon

Hollywood wrote: I went round and round with this in my head last week. I've settled on 5/8" off the intake manifold and 1/2" out of the core to a simple T before the RWP. .

So, did you just now plumb it this way or have you been running it like this for a while? Also, I thought the manifold tap (where the temp sender is just before the thermostat housing) is 1/2", not 5/8 (although maybe it is, I'll have to look again).

I already have a valve to shut it off; I'd just need to get a T just before the RWP. Please le tme know if you have been running it this way, and how the temp is on the engine and heater, especially when the lake water is cold (ours gets down to a little below 50 and I ski year around).

Hollywood wrote: I have not run this yet. I will install it in the spring time. I'm aware the manifold port is likely not 5/8" npt, an adapter will be needed for my application. If someone wants to fund this research ill install it next week...

I don't remember what size, but I put a stub in, a 45 degree elbow, a T for the temp sensor, and a hose bib. Can't remember the size (did all that right after we got the boat, but bigger than the block plugs.

I've got the standard setup with the Y, I think part of the issue, at least in my case, is the run from a motor in the back to the front of the boat.   Last year I added some pipe insulation from the motor as far forward as I could get it. Seemed to help a little, I think I used about 10 ft, and I may try to add some more when I change out my hoses to move my quick disconnects.   I think a big thing is that the boat doesn't run near as hot as a car which is the standard you expect to a heater.

I've wondered what enlarging the small hole would do fo increasing the flow, but don't want to be the first to try it.   Im not sure you are going to get much out of it since you already have the pumps helping with the circulation.

slmskrs wrote: gun-driver wrote: Use the "Y" fitting before the raw water pump. Water going to the raw water pump draws the water from the Y better than a T fitting improving circulation. After I installed the Y fitting heat at idle improved greatly. I just got the Y fitting. I can't believe how small the hole is in the return on the Y. It seems that I'm not going to get anywhere near the flow I'd like for maximum heat. Since the engines run cooler than car engines, you need more flow so the heater core temp doesn't drop as much. Since I bought the Y fitting, I'll go ahead and put it in and see how it works. Thanks,

Dont forget that the Y fitting is a custom made piece, designed specifically to increase heat output at idle. It would have been easier to manufacture that Y without the reduced diameter at the outlet, so...

One would assume that the small orifice was intentional, and critical to improving heater output. It seems counter intuitive to some degree, as I would agree that maximizing flow would usually be the goal... but Im guessing theres something Im missing. Either on the pressure vs. velocity vs. cross sectional area relationship (somehow that reduced orifice improves flow?), or perhaps the intent is to slow the flow down through the core, giving the core more time to heat up before the water moves through it? Someone with a better grasp of fluid dynamics might be able to shed some light.

My dad has improved the heat output of a few heaters by building in his own reduction tee at the return... so its a repeatable phenomena (theres nothing magical about the Y).

Oh, one other thought I've had. I could get another shower pump (chamber/valve demand pump rather than cyntrifical) since demand pumps run dry and will pull air through. However, I don't know if they are continuous duty or how long they'd last pumping hot water for hours at a time non-stop. But that would eliminate the air issue since it would just pump the air right through with the water..... :)

Ha, just found a continuous duty, self priming pump (up to 180F) on line that has an impeller similar to our raw water pumps. This sucker will take care of any air in the line. This just might work..... :)

I will have to pull out the 'ol IR themometer. Hadn't thought of checking temps that way; maybe it will be hotter than I've been expecting. I'll check tomorrow and see what I find out.