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[KeelsonGraham]

OK, this is going to sound really dumb to you experienced old hands, but how do you top up the fresh water coolant on an M35? Via the header tank, or via the water cap on the engine?

[Jim Hardesty]

how do you top up the fresh water coolant on an M35

Just like your car.  Fill the expansion tank to the mark.  The coolant should be full to the pressure cap.  If it's not top it off.  If the coolant is very low may need to burp the system. 
Hope that helps,  a question is never dumb.
Jim

[KeelsonGraham]

Thanks Jim. That’s what I’ve been doing, but the engine runs hot and the expansion tank always seems dry.

So, I read one method for burping the system which involved watching the flow into the expansion tank until no more bubbles appear. Seemed to imply a cold system. That got me wondering if the expansion tank should normally have coolant in it even when cold. Hence the dumb question!

[Ron Hill]

Keel : If the recovery tank goes dry - you are loosing coolant somewhere!!  Make sure your pressure cap is on tight!

The first items to check are on the hose clamps.  If you haven't put oil diapers under the engine and on the sides do so!! -  so you can find out if and where you have an external leak!!                                     
Sure hope it's not an internal leak!?!

A few thoughts

[KeelsonGraham]

Thanks Ron,

So in normal use, even when cold, the recovery tank should have fluid in it?
EDIT: Just read Jim’s comment properly! Seems like I've been running it with too little coolant ever since I bought it.

[Jim Hardesty]

Keelsom, If memory serves me correctly the expansion tank is about half full cold.  PO put tape at full line.  Shamrock doesn't loose coolant.  Go multi seasons with out adding.   In addition to Ron's suggestion, take a good look at the coolant pump, if that's leaking it's often a spray when running but no drip when not.  Next step would be to go to an auto store that rents or loans tools and get a pressure tester.  That will tell you if you have a leak.
FWIW Shamrock never runs hot.
Jim

[scgunner]

Keelson,

It sounds like you've got a couple of things going on here; possible coolant loss, and running hot. First things first, generally when filling water cooled engines you fill to the bottom of the tank or radiator cap neck. If you overfill the system it will expel the additional coolant after a couple of run cycles. If you're continually losing coolant you need to find out where it's going before you can fix it. If you do have a leak it's probably not internal unless you've got a lot of white steam coming from the exhaust.

It's not clear from your post if you've just been running with low coolant or you've been adding  coolant and it keeps running low. In either case you probably have air in the system which combined with low coolant would certainly lead to over heating.

If you have a leak and fix it then you can top up the tank, if at that point the motor runs normally you're good to go. If it overheats there's probably air in the system and you'll probably have to burp it. While there are a number of ways to burp the system I've found this one to be the easiest. Remove the cap, place rags around the neck, start the motor then goose the throttle a few times, 1500 rpms should do it. The coolant will bubble out the opening (reason for the rags) along with any trapped air and the tank level will drop. Then just top it up and you're good to go.

[Ron Hill]

Keel : The "coolant recovery" system that you have on your C34 is identical to the coolant recovery system that you have on your auto/s.
It is a closed system. When the engine runs the coolant heats and expands. The "overflow expansion" goes in to the recovery bottle and when the engine cools the coolant contracts and moves from the recovery bottle back in to the engine.  There is never a need to remove the "radiator cap" and check - just look at the bottle level!  The bottle should have 2 markings - Hot/Warm and Cold

What you need to do is start over by refilling the system with 50/50 mix of water/Prestone(full strength) (or pre mixed 50/50). Remove the cap and fill the engine reservoir and fill the recovery bottle to the "cold" mark.  The "burping of the engine" is when an air bubble gets caught (usually) in the hoses to the water heater.  If you have that air bubble the engine will heat up and start to overheat (because the coolant is NOT moving by being blocked by that bubble)  Look in the Critical Updates and Burping posts to clear that bubble - so the coolant flows freely.

Like I previously posted, I believe you have a leak somewhere??  Hope this explanation helps.

A few thoughts

[KeelsonGraham]

Thanks guys. Great info.

I too am not clear whether I have a leak or have simply been running it with not enough coolant. I bought the boat 18 months ago and the PO pointed to the expansion tank and said something like “it never seems to fill so I don’t touch it”. So, I took it from that, that I never needed to look it. Now, I’m going to pay it some close attention.

The engine starts to run hot if I run it above about 2100 RPM. The temp gradually rises to about 180 and there is a little steam evident in the exhaust. However, this could be an issue with the raw water side. I’m a little suspicious about the through flow. The discharge from the exhaust seems a little feeble to me.

I replaced the impeller, I’ve checked the thru hull and the water strainer. No obvious reasons for a blockage. So, next investigation will be the HX.

It’s really frustrating not having good manuals for the boat and engine. Thank heavens for this website and all your great assistance.

[Jim Hardesty]

It’s really frustrating not having good manuals for the boat and engine.

Keelson,
In case you don't know, the manuals are here.  From the home page click manuals.  I've loaded them onto my computer.  That way I have them even without a Wi-Fi connection.
Shamrock has the same engine and cooling system as you do, never overheats.  Even towing a 42 foot center cockpit all day.  The water flow from the exhaust isn't a steady stream like some, more like splashing and spray.
Because you inherited the problem think you need to check out the entire systems, both the engine circuit and the raw water side.  I would start by checking for coolant leaks and get the system full and circulating. 
Curious, how is your hot water?  If the coolant doesn't circulate it won't heat up the hot water tank. 
Jim

[KeelsonGraham]

Hi Jim.

I have the PDF manuals. The Westerbeke one isn’t specific to Catalinas so it’s of limited use for routine maintenance. The Catalina manual has almost nothing in it of use.

That’s a good point about the hot water. Yes, it’s fine.

As soon as I get the boat back in the water, I’m going to go through everything. My money’s on insufficient coolant level.

[Ron Hill]

Keel : I'd remove the pressure cap and fill the engine reservoir replace cap and fill the recovery bottle to cold.  Then run the engine to operating temp.  Let the engine cool to cold and see what happens to the recovery bottle.  If you can run the engine to 2100 rpm I don't believe that you have an air bubble blockage - just VERY low coolant.  Try it and let us know

A few thoughts

[KeelsonGraham]

Will do Ron. But she’s not back in the water until the end of March. If I try this in the yard she’ll definitely run hot!!

Running at 2100 will be fun because I’ve yet to find neutral on this boat 🙄

I guess I’ll just have to double up the warps😂

[Ron Hill]

Keel : Before you go into the water take a half hour and with a screwdriver or nut driver and check ALL of your hose clamps to make sure they are tight.  Don't try to KING KONG them - just tight!!  Then fill your recovery bottle to the HOT level.  Just leave the engine pressure cap closed. 
I feel the your system is just very low on coolant and if I'm correct; when you run the engine to operating temp it will cool down and suck coolant back into the engine. You will probably have to add coolant to the recovery bottle.

On your transmission neutral - Go down below so you can look at the starboard side of the transmission under the aft cabin. You should be able to move the shifting lever by hand. All the way forward is Reverse gear and all the way aft is forward gear.  Half way in-between is neutral (straight up).  In that half way point you should be able to turn the shaft by hand easily in both directions.  Then go to the wheel and look at the position of the Shifter!!  The cable should be connected to the shifter lever on the transmission in the low hole on the shifter lever. 

A few ideas - hope this helps!?!

[KeelsonGraham]

Thank you again Ron for such helpful advice.

LA Lady’s feel at the telegraph handle is like nothing I’ve experienced on any other yacht. There seem to be two ‘slack’ spots, both aft of the mid (vertical) lever position. Neither of them actually result in neutral!

Checking transmission adjustment is one of the many things on my ever-growing to do list!