Overcooling

[Ron Cooper]

I'm trying to figure out why my 1968 raw water cooled A4 does not heat up to a proper operating temperature. The heat sensor appears to be operating, if I restrict the inflow of water through the seacock it shows the temperature rising. The previous owner had put in a bypass shut-off valve, and right below that they put a one-way valve (like an anti-siphon). See the pic with the white arrow. Is there a reason to have a one-way valve there? If not, I'm thinking of taking it out to improve the flow through the bypass which may allow the temperature to rise. Does that make sense?

[Dave Neptune]

First welcome to the MMI Forum.

I have not seen a check valve in the bypass line and can see no reason for one.

You mention closing the seacock to increase the temp by reducing the water flow. Do you mean the one for the thru-hull? If so it is not what you adjust. The valve in the bypass line is what you adjust. From the looks of that valve you are set for maximum temp (all the water is being bypassed) IE minimum cooling. When the valve is closed it is (forcing all the water through the block) at max cooling. You can adjust to suit for the temp of the water you operate in.

NOTE~~when using a valve in the bypass loop for temp adjusting the temperature response is slow. Also at idle and low speeds the temp will stay lower than set for at operating or cruising speeds. Set the valve when at operating speed or slightly above and adjust to 130~140 degrees which is sufficient for good performance and longevity.

Dave Neptune

[ndutton]

In addition to Dave's reply, closing or restricting the raw water intake thru-hull risks overheating the exhaust system to the point of damage or destruction in short order. That temp won't show on your gauge.

Don't know what you're expecting from a raw water cooled engine. Back when mine was RWC the running temp rarely reached 120°. The engine must have thought it was running in the Arctic Circle.

[joe_db]

My engine rarely gets about 120-125 even with the bypass open unless run very hard for some time in warm water. It seems to have done it no harm at all.

[Dave Neptune]

More thinking

Ron, upon further thought I neglected the pressure it takes to open the check valve. The check valves open at various pressures depending on application. So even with your "bypass valve" completely open there may be enough spring resistance in the check valve to still force most of the water through the block thus your "running to cool" issue.

Dave Neptune

[GregH]

In addition to Dave's reply, closing or restricting the raw water intake thru-hull risks overheating the exhaust system to the point of damage or destruction in short order. That temp won't show on your gauge.

Don't know what you're expecting from a raw water cooled engine. Back when mine was RWC the running temp rarely reached 120°. The engine must have thought it was running in the Arctic Circle.

No Arctic Circle but L. Ontario (on the northern side no less ) and it is tough to get up to 120F at times.

[Al Schober]

Another thought on this issue.. Cooling water enters the block through a pipe nipple in the side cover plate. There's a Tee fitting on the outside to accept water from the pump and send bypass water to the thermostat housing.
This pipe nipple is supposed to have a cap on the inside, drilled to direct the water towards the transmission end of the block. Perhaps this cap has fallen off or has been drilled oversize? This would tend to flood the block with coolant regardless of the setting of the bypass valve.

[Ron Cooper]

Thanks for all the helpful and timely replies!
I do understand the bypass valve operation and the danger of overheating the exhaust system when shutting off the water intake valve. I did that carefully just to test the temperature sensor.
So my question was really about that check valve, why would that have been installed and is it needed for anything. And it sounds like nobody has seen that before?
Dave, you're right, I was able to open the check valve by blowing through it but I had to blow quite hard, so it definitely is restricting the flow to some degree, and may not actually be opening at all!
Al, I didn't know about the nipple on the T valve, thanks for noting that as a possibility, I hope that's not it!
It's helpful too see that others have been running for years with the motor never getting over 120. I'm in Belfast, Maine, so the water's not that warm here either - especially at the end of November when solo sailing and a lobster pot line gets wrapped around the prop shaft! (I now carry a wet suit on board). The thing that started me trying to get the temperature up is that my plugs have been fouling. So, unless I learn from someone that this check valve is a good thing, I will remove it, see what effect that has, and then of course see if I might be running a bit rich or need to try hotter plugs(?). By the way, it has an electronic ignition.
-Ron
1968 Alberg 30 #345

[msmith10]

I have an identical check valve on my engine. I think this was sold as part of a package by MMI many years ago (15?) as part of a conversion to an off-the-shelf thermostat to replace the double acting Holley, and the install instructions said it was necessary for some reason which I don't remember. Came along with a spacer to raise the thermostat cover, and the bypass shutoff valve. Shortly after that Moyer switched to a different off the shelf thermostat and I don't know if the kit for that unit contained those other parts. I don't think they sell the latter kit anymore either.
I see from your photo that you do have the spacer installed. I would bet you have the same thermostat I use and the PO bought the same kit from MMI at around the same era. Don't remember what the check valve was for, but I do remember that it came with the kit and instructions said it was necessary to install it.
I'm a couple of hours away from my boat, and it's now put to bed for the winter so I can't access the instructions that came with the kit, if I still have them.
Just looked on the Moyer site and they still offer that check valve under "cooling- other". 3/8". I think mine is 1/2.

[B Moyer]

over cooling

Your engine temperature is actually controlled by the thermostat modulating flow through your bypass loop (between the "T" fitting on the side of the engine and the inlet to the thermostat housing). Restricting the bypass flow forces more coolant through the engine for cooler temperature (which seems to be your case), while opening the bypass loop raises the temperature. With no added restriction in the bypass loop, engine temperature will usually run somewhere between the temperature at which the thermostat starts to open, and the place it is fully open (150 - 180 degrees).
In our earlier engines, we added a spring loaded check valve in the bypass loop (as in your photo). Later, we added a ball valve to provide a manual ability to force even more water through the "T" fitting (and through the engine) if some problem developed within the cooling system. Still later, we removed the check valve (which you can do) feeling that it was a bit of over-kill with the manual ball valve.
If you can tolerate a longer discussion of late model by-pass cooling systems, you can go here: https://moyermarine.com/nljune2018/

[AtomicBaby]

Your engine temperature is actually controlled by the thermostat modulating flow through your bypass loop (between the "T" fitting on the side of the engine and the inlet to the thermostat housing). Restricting the bypass flow forces more coolant through the engine for cooler temperature (which seems to be your case), while opening the bypass loop raises the temperature. With no added restriction in the bypass loop, engine temperature will usually run somewhere between the temperature at which the thermostat starts to open, and the place it is fully open (150 - 180 degrees).
In our earlier engines, we added a spring loaded check valve in the bypass loop (as in your photo). Later, we added a ball valve to provide a manual ability to force even more water through the "T" fitting (and through the engine) if some problem developed within the cooling system. Still later, we removed the check valve (which you can do) feeling that it was a bit of over-kill with the manual ball valve.
If you can tolerate a longer discussion of late model by-pass cooling systems, you can go here: https://moyermarine.com/nljune2018/

Is standard operating temp still 140 to 160 for RWC on late models ? All the Moyer info suggests it is, but alot of anecdotal info, like on thread above, suggests 120. Would running as low as 120 not cause carbon buildup or other problems? Should I be concerned at running at 140 to 160? Thanks!

[Dave Neptune]

No. the lower temps are mostly related to wear and only slightly to thermal efficiency. For good thermal efficiency you need to run over 200* and that is not good in salt water. Carbon deposits and or plug fowling are caused by poor timing and/or to rich of a fuel mixture. Oil fowling is caused by wear of the rings, mostly to "lower oil ring". I ran for 34 years at 120~135 with absolutely clean creamy tan colored plugs. I changed plugs every 2~3 years and the cap and rotor every 5~6 years with an EI. Never a let down, not once.

Dave Neptune

[joe_db]

No. the lower temps are mostly related to wear and only slightly to thermal efficiency. For good thermal efficiency you need to run over 200* and that is not good in salt water. Carbon deposits and or plug fowling are caused by poor timing and/or to rich of a fuel mixture. Oil fowling is caused by wear of the rings, mostly to "lower oil ring". I ran for 34 years at 120~135 with absolutely clean creamy tan colored plugs. I changed plugs every 2~3 years and the cap and rotor every 5~6 years with an EI. Never a let down, not once.

Dave Neptune

I too cannot point to one problem from running cool. BTW, you all might want to think about an oil temperature gauge. Last time I put my FLIR camera on the oil filter it was hotter than the coolant. Cold OIL is what causes problems
Also note as shown that the valve side of the engine doesn't seem to have much if any coolant over there and still gets plenty hot.

[Ron Cooper]

Update

Mark, you're right, my setup, like yours, is using an earlier MM kit. Ken at MM diagnosed it all for me. The odd thing is that the Tstat is not the one that came with that kit, it is an earlier (original?) double-acting one. Following his suggestions, I left the spacer on, kept the Tstat, and just removed the checkvalve from the bypass loop. And voila, after 5+ min in forward at the dock, temp got up to 140.
Another thing is that the inside roof of the Tstat was of course rusty and there was a lump on the rim of the bypass opening, so I did grind that down a little to hopefully allow the top plate of the double-acting Tstat to seal it off better.