Overheating when I hook up the cabin heat

[kellydee]

2007 Mercruiser 5.7L carbed full FWC with engine mounted seawater pump. Runs perfect but,I overheat every time I try to hook up the cabin heat.I have read that you have to bleed the air out of the system.I've tried loosening the hoses at the top of the manifold (bypass), but no luck.Is there some trick to this or what?I have the supply from the top of the intake to the bottom of the heater and from the top of the heater back to the water pump.Is this correct ? This is the third time I've tried to hook up my heat and just can't seem to get it.Can anyone give me some how-to on this one? I really don't want to have to go another season without heat.Brrr, it's cold at the ocean right now but it's halibut time. Thanks,Jerry.

 

[JCF350]

Re: Overheating when I hook up the cabin heat

Are you refilling during initial warm up? Thermostat needs to have time to be open for the coolant flow through system.

Heater must be lower than the refill cap also.

 

[kellydee]

Re: Overheating when I hook up the cabin heat

I let it warm up,t-stat opened and coolant went into the res bottle.After that,the water in the exchanger wasn't even getting hot but,everything else was.I don't think it is the t-stat as it is only 1 yr old and I just ran the motor without the heat hooked up 2 days ago.Let it run for at least 1/2 hr with no trouble.Yes, heater is below the tof of the exchanger.I'm not actually adding a heater.It was hooked up to the old motor and worked fine.Now I have a new motor and can't seem to get the heater to work without overheating.

 

[Don S]

Re: Overheating when I hook up the cabin heat

On the newer models, I think you have to hook the supply line up to the thermostat housing. There should be a pipe plug on the housing where you put in the barbed fitting.

 

[kellydee]

Re: Overheating when I hook up the cabin heat

Don, I used an after-market cooling kit(San Juan) which had me replace the housing with one that has no fittings or a place for one.They had me remove the plug from the top of the manifold just starboard of the t-stat(now I don't remember if there was a plug or sensor) and install a cross with the temp sensor .This is where my bypass hose goes.From here to the water pump.(no heater hooked up).

 

[kellydee]

Re: Overheating when I hook up the cabin heat

Don, I sure hope you're wrong but,I won't count on it. Last year when I put this motor in,everyone EXCEPT YOU(including my merc dealer who ordered this for me),said I didn't need to add an engine driven sea-water pump.After all else failed,that addition solved the problem.I did have one other local(but not so local)mechanic tell me he just could not get the San Juan kit to cool properly.He changed it to a Merc Kit and no more problems. I'm preparing myself for a huge fit.

 

[kellydee]

Re: Overheating when I hook up the cabin heat

a couple pics

 

[JCF350]

Re: Overheating when I hook up the cabin heat

I let it warm up,t-stat opened and coolant went into the res bottle.After that,the water in the exchanger wasn't even getting hot but,everything else was.I don't think it is the t-stat as it is only 1 yr old and I just ran the motor without the heat hooked up 2 days ago.Let it run for at least 1/2 hr with no trouble.Yes, heater is below the tof of the exchanger.I'm not actually adding a heater.It was hooked up to the old motor and worked fine.Now I have a new motor and can't seem to get the heater to work without overheating.

Some installations of those kits need a 12 volt circulation pump installed in one of the hoses going to the heater (different engine). If the heater doesn't get warm your not flowing coolant through it (might not even be getting there). Might need to cycle through a couple of warm ups to make sure your full of coolant.

If you have make and model of heater. Contact them. Installation manuals are often available on line.

 

[kellydee]

Re: Overheating when I hook up the cabin heat

The heater is getting warm but the engine is overheating.

 

[JCF350]

Re: Overheating when I hook up the cabin heat

Edited

Sounds like your parallel flowing to much coolant through the heater and not enough through the exchanger. Looking through the Martec site they only show a t-stat hsg connection for the heater.

This statement "I let it warm up,t-stat opened and coolant went into the res bottle.After that,the water in the exchanger wasn't even getting hot" tells me that with the heater connected the way it is may be the case and the cause.

 

[kellydee]

Re: Overheating when I hook up the cabin heat

I kinda see what you're saying but, without the heater connected, there's only about 16" of hose from the manifold to the water pump.Runs perfect. If I remove that hose and run 10' to the heater and 10 ft back,I don't see how that would create MORE flow.

 

[kellydee]

Re: Overheating when I hook up the cabin heat

A ll I can figure is it must be air.I just disconnected it again and she runs perfectly. Guess I'm fishin without heat this week. Headed for Neah Bay tomorrow for Halibut.When I get back, I'll give it another shot.

 

[Uraijit]

Re: Overheating when I hook up the cabin heat

I kinda see what you're saying but, without the heater connected, there's only about 16" of hose from the manifold to the water pump.Runs perfect. If I remove that hose and run 10' to the heater and 10 ft back,I don't see how that would create MORE flow.

Because that's the nature of the beast. It takes more pressure to push water over that longer distance, up through the heater core, and back down. When you just have a straight 16" shot, there's less resistance, hence the water flows freely.

 

[JCF350]

Re: Overheating when I hook up the cabin heat

Go fishing!! will discuss more when you get back.

 

[kellydee]

Re: Overheating when I hook up the cabin heat

Go fishing!! will discuss more when you get back.

 

[HT32BSX115]

Re: Overheating when I hook up the cabin heat

Get a 1/2" brass ball valve from Home depot with hose bibs on each end. put it in series with the heater core and close it.

Then run the boat and open it a little at a time and see where it gives you heat but doesn't cause an over heat.....You'll probably find a setting that works. you don't need all that much flow thru the heater core anyway.


fill the heater core and hoses first (low-to-high to eliminate air)