1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

[VerBoatin]

Hello Mercruiser Experts,
I just purchased a boat with 1990 Mercruiser 454's. I'm having a little trouble figuring out if the engines are FWC or if they are 1/2 FWC engines. If you can tell my looking at the attached photograph, I would be most grateful for your assistance.
The reason I am asking is that I want to install a heat exchanger/electric water heater versus the electric only water heater now installed. I am trying to figure out where to install the fittings to "tap" into the cooling system, route it into the new water heater, and back to the system. I "think" I know how to do this but would appreciate the verification. Again, many thanks for any advice.

 

[Bt Doctur]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

engine and manifolds are FWC, riser/elbow is raw water cooled

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

engine and manifolds are FWC, riser/elbow is raw water cooled

Thanks much Doctor! I appreciate the quick feedback. Sir, would you be willing to make a recommendation, based on the photograph, where I should disconnect the cooling system and route it into the hot water heater and then back to its original fitting? Thanks in advance! VB

 

[Bondo]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Thanks much Doctor! I appreciate the quick feedback. Sir, would you be willing to make a recommendation, based on the photograph, where I should disconnect the cooling system and route it into the hot water heater and then back to its original fitting? Thanks in advance! VB

Ayuh,.... Welcome Aboard,.... Can't see in yer picture, But,...

There should be a 1/2" pipe plug in the intake manifold, just aft of the T-stat housing....
The Hottest water in the motor,... normally...

The circulting water pump housing should also have a 1/2" pipe plug in it,... That's yer return flow...

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Thanks much for pointing out the "plugs"...
I found both...one in the intake manifold...the other in the pump.
If you don't mind clarifying one point....I will be using the pump (plug) and fitting a hose to run the water TO my hot water heater and then the return line (back into the engine) will be to a fitting that replaces the plug in the intake manifold, yes?
Thanks for the information and your time!
VB

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

I attached two photos...one of the intake manifold plug and one of the water pump plug...thanks again...VB

 

[Bondo]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Thanks much for pointing out the "plugs"...
I found both...one in the intake manifold...the other in the pump.
If you don't mind clarifying one point....I will be using the pump (plug) and fitting a hose to run the water TO my hot water heater and then the return line (back into the engine) will be to a fitting that replaces the plug in the intake manifold, yes?
Thanks for the information and your time!
VB

Ayuh,..... 1st off, that's the wrong plug in the intake, I believe that plug goes to the intake runner, 'n not the water jacket...
There should be another 1, much closer to the T-stat housing...

And, you've got it Backwards above...
The intake manifold, under the T-stat, has the hottest water, at the highest pressure...
The plug in the water pump housing is the return, as that's the low pressure point...

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Hi Again Bond-O,
In the remote event I cannot find a plug behind the T-stat as you describe (I didn't see one but I'm going to check again)....would it permissible to "T" off of the hose that runs into the thermostat fitting or is that a no-go? Thanks in advance. VB

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Sir,
I think I may have answered my own question....please see the attached photo and there is, sure enough, another plug near the T-Stat housing. Would this be the plug to which you are referring?
Thanks again in advance...VB

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

I think I found the plug to which you refer...please see attached photo...I have a white arrow on the photo pointing to plug...located right next to the t-stat as you said. This would be the line going TO the water heater and then the line returning to the engine would go into the water pump...again...as you stated (but I had it backwards)...Thanks much! VB

 

[Josh P]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

That is the plug you want...good luck

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Hi Josh,
Thanks very much for your post and reply to my inquiry. I really appreciate the help and confirmation! Nice truck by the way!
VB

 

[Speakrdude]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

By-the-way, if you ever want to connect a vaccuum gauge to your engine, The first picture of the plug behind your carb is the one.
Good luck getting thos plugs out. They can be a real dog. I've broken off two in the intake manifold before, haveing to drill out and retap. No fun.

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Hi SpeakerDude,
Thanks for the information about the intake manifold vacuum gauge and for the warning about getting the plugs out. Is there anything I might do in advance, perhaps spray some WD40 into the threads and let it sit for a few days, etc...to lessen the chances of breaking one off? By the way, what size are the plugs? Do I need a 1/2 inch NPT fitting with a barbed hose fitting on the end to connect to the heater/coolant hoses running back to and from the heat exchanger? Thanks much! VB

 

[VerBoatin]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Hi Speakrdude,
Well...as you said...no fun. I was able to loosen the lower plug ~ the one on the pump, no problem at all. However, the one in the intake manifold broke off as soon as I put some torque on it so I have only a corner of the original square fitting (the fitting portion I refer to is the part that would accept a standard socket driver). May I get a recommendation from you on drilling out the plug and a retap of the plug itself so it will accept a 1/2 inch fitting? Do I drill a small hold in the plug and try an easy out tool or do I need to simply keep drilling the hole larger and larger until I get very close to the size of the plug threads...then remove the plug threads if possible and retap/clean out the threads a 1/2 inch tap? I've done this a few times with other things and got to the point where I drilled a large enough hole that only the threads were left around the circumference of the drilled hole. I could actually pull the threads appear rusted, etc. Any and all recommendations are most welcome! I attached two photographs of the plug as it appears now...with the sides broken off, etc. (The liquid you see around the plug was liquid wrench I tried - let it sit for about a week to see if it would work to help loosen the plug...no luck)

I have one additional "short cut" question. Would it be possible for me to simply add a "T" fitting to the 5/8 in hose that it attached to the thermostat and run that to the water heater "IN" rather than go through the drilling and tapping of the plug? The 5/8 in line I refer to is shown in the photo with the arrow pointing to the plug...its the hose just below the white arrow.

Thanks in advance for your assistance. VB

 

[Speakrdude]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

Drilling and tapping that plug is pretty simple and easy to get to. I don't think the 5/8's fitting would allow enough flow, but just guessing on that one.

 

[Comogene]

Re: 1990 Mercruiser - 454 Engine - Cooling System - Hot Water Heat Exchanger Hook Up?

VB:

I had the same project over the winter and the same problem. Drilling out the plug in the manifold was time consuming but not difficult. The process you described is the way to go, increasingly larger bits. Keep a vacuum handy to suck up the metal filings and I liberally douse the bits with Mystery Oil. Since I used 90 degree hose barbs, I had to increase the height by adding an extension which was not a big deal.

It does not matter how the hoses from the water heater run - it is a circuit. The key as noted by Bondo is positive water pressure on one side and negative on the other which you will have using those two locations.

Gene