Atomic 4 overheating

[kbgunn]

I'm negotiating a 1982 Catalina 30 with an Atomic 4 gasoline engine that is raw water cooled. The survey was today and found only one major issue.

The engine overheated in the following way. Engine started and warmed up to about 160 degrees. Ran for 10 minutes at idle. Adequate cooling water discharge was observed. Surveyor shut down the engine for 30 mins. Started the engine. Warmed up to 160 at idle. Engaged forward gear and opened throttle to about 3500-4000 rpm. The engine overheated with temp spiking over 200. Shut down engine. Some soke from engine compartment and surface reading on the engine head were 210-220 at various places.

Any ideas what cause the overheating with cooling water flowing?

Every other aspect of the boat was solid.

Thanks,
KBG

[Dave Neptune]

KBG, first welcome to the MMI Afourian Forum.

First lets talk RPM I've never seen an A-4 get that kind of RPM tied to a dock even one with a reduction unit. In the C-30 it is probably a direct drive (1500~2200 RPM's) and getting past 2000 requires a lot of prop work.

Now for the heating with good flow. First is it raw water cooled or is there a heat exchanger? Is there a thermostat installed and/or a bypass valve to control temps.

It is not hard diagnosis just need some info.

Dave Neptune

[kbgunn]

Thanks for the reply Dave. I appreciate the warm welcome!

It is a raw water cooled engine fed directly from the through hull. No heat exchanger. Fresh water lake boat. It has a thermostat installed to control water flow into the manifold as the engine warms up.

As for the RPM, I was keeping an eye on the tach so I know that's accurate. Are you saying the engine was over-revved and that's what caused it to over heat?

[Dave Neptune]

KBG, as far as the RPM's it could also be the tach is on the wrong setting not to uncommon. I doubt the RPM's have much to do with the heating.

Is there a line that runs from the water injection point on the side of the block (a tee) up to the thermostat housing and is there a valve in that line?

The water needs to circulate through the block. When the t-stat is closed the water is rerouted through the bypass line to the exhaust manifold skipping the "block". So we need to know if the t'stat is good. It can be easily removed and checked in a pan of hot water with a thermometer to check the opening temp.

Many many of the A-4's running today do not use a t'stat ie it is removed. When removed the bypass valve is used to regulate engine temps. I ran like this for over 30 years on the same motor that is now running for someone else. Valve closed max cooling as it all goes through the block~valve opening bypasses the block to increase temps and still all the water goes out the back.

If you remove the t'stat just put the housing back on and give it a try IF YOU HAVE A BYPASS VALVE. Then monitor the heat. Don't worry about using an IR gun for checking head temps watch the gage. Due to the flow pattern of the water and a "flathead" design there a many varying temps on the head when running.

Dave Neptune

[ndutton]

A blockage in the block and/or head could cause the overheating but because of the bypass style cooling system that delivers full flow through the manifold at all times you would not notice a change out the exhaust. This suggests to me an acid flush is in order at a minimum, perhaps opening the water jacket side plate and physically mucking out the water jacket.

As for the RPM, I was keeping an eye on the tach so I know that's accurate. Are you saying the engine was over-revved and that's what caused it to over heat?

Please reconsider Dave's comment. With a direct drive A-4 and Catalina's typical 12 x 7 fixed two blade prop it's simply not possible to achieve 3500-4000 RPM in forward gear. Out of gear, yes but in gear, no way.

[kbgunn]

I will have to re-check the cooling system configuration to see if a bypass valve is installed. It will require a trip to the boat. Thanks Dave and ndutton for sharing your experience with a newbie. All of my previous experience is with outboard motor so this is all new territory for me.

-KBG

[JOHN COOKSON]

It is a raw water cooled engine fed directly from the through hull. No heat exchanger. Fresh water lake boat. It has a thermostat installed to control water flow into the manifold as the engine warms up.
As for the RPM, I was keeping an eye on the tach so I know that's accurate. Are you saying the engine was over-revved and that's what caused it to over heat?

The thermostat may be broken and stuck in the closed position. This would force the cooling water to go around the engine by way of the bypass rather than through the engine
The tach may be set for an eight cylinder engine which would make the four cylinder reading 1/2 the actual reading.

TRUE GRIT

[zellerj]

Overheating on an Atomic 4 is fairly common and easy to fix. I would not let it be a "walk away" issue, but possibly a negotiating issue. Fixing it requires checking out the thermostat and the thermostat housing, making sure the mixing T is clear of old broken impeller vanes, checking the water exit elbow on the exhaust manifold, and as Neil said, removing the side plate and getting rid of 36 years of crap. With good water flow and high operating temps, the water is not circulating around the cylinder tubes and head like it should. There has to be a blockage somewhere, and finding it and fixing it is usually not that hard to do.

[kbgunn]

Overheating on an Atomic 4 is fairly common and easy to fix. I would not let it be a "walk away" issue, but possibly a negotiating issue.

Good to know it's not a major issue. It's a solid boat with no water intrusion in the plywood core and very minimal cracking in the gelcoat. I will definitely use the overheating as a bargaining point.

[CajunSpike]

Just had to fix an overheat on my A4. The manifold outlet was clogged. Stuck a screwdriver in the outlet hole...wiggled it around.

Freed up the clog and now so cool it doesn't show on the temp gauge.

[Sam]

I think worst case is you have a somewhat worn impeller or water pump. It would still have fair amount exhaust flow out he back but it is hard to determine if it is 10 -20 - 30% less if you haven't had the boat for while. Impeller $35, water pump about $300 with an hour of simple labor. There is a rebuild kit available as well. On the late model engines with a thermostat 160F is standard with raw lake water. I had same problem with my early model A4 few years back - changed pump to bigger oberdofer pump and temp cooled down to 140 F. Good luck, definetly not a deal killer.

[Al Schober]

Definitely not a deal killer. If the present owner pays to have it corrected, give him his price. If it's an as-is sale, it's worth negotiation as you're buying his problem.

[sastanley]

KBG, WELCOME!
Be sure to check the 360° panoramic motor on the home page here..We can use that as reference to make sure you know all the parts being referenced in this discussion. The Bypass Dave is referring to is the copper pipes with the silver valve in the middle over on the stbd side of the engine..this can adjust/regulate the amount of cooling water being forced into the block. The t-stat housing is in between the copper tubes and the red hoses on top of the head.

[kbgunn]

That 360 photo is a good resource. I don't think I have the bypass valve. I don't have a good photo but you can kinda see in this one:


I don't have access to the boat at the moment. It looks like the bypass is an after market mod? Probably one that is worthwhile since it eliminates the need for a t-stat?

[CajunSpike]

The bypass valve is circled in this motor shot.
Other than connecting the hose to a valve, then to the thermostat cover, there's not much to it.