Engine overheating problem (with Instructions "How To Burp!")

[Bill Asbury]

Following a recent cruise in which required motoring at least four hours I found quite a bit of coolant (50/50 antifreeze) in pan under engine.  Traced leak to HX hose connection on port side under manifold.  Decided to replace original-looking hose plus the hose it connects to in front of engine, and double clamped the HX connection, which stopped the leak.  Topped up coolant and ran engine, which overheated right away (first time in three years of ownership).  Referred to manual which said replacing coolant can induce air into system and suggested running engine up to 2800-3000 rpm momentarily to dispell air from system, which might take 2-3 repetitions to do the job.  Still overheating.
Checked following:
HX zinc - OK
Thermostat - OK
Raw water strainer - OK
Raw water discharge - OK
Opened fresh water bleed valve

Perhaps someone can diagnose this problem from experience.  Could double-clamping that connection cause the problem?  It was previously single-clamped. Something is apparently blocking coolant flow.
Thanks in advance for any suggestions.
Bill
   

[Jeff Kaplan]

bill, so long as both hose clamps are tightened onto  the barb, there can be no restriction, but if the outer clamp is tightened just, or partially onto the hose, this will cause the restriction and lead to overheating. check for this, and also, as you run the engine, leave the rad. cap off and check to make sure you don't need more antifreeze...jeff

[Ron Hill]

Bill : It sounds to me as though you didn't "burp" all of the air out of the internal coolant system.  We've post this many times. 

[Bill Asbury]

Thanks for your quick responses Jeff and Ron.  Did check coolant level after running engine 3 times and  level is as specified in manual.  Tomorrow will loosen outer hose clamp and run engine again to see if that might have caused restriction, which I thought about after leaving boat and suspect might be the case.  Also thought there might be air blocking coolant flow and so did what manual suggested, running engine  at high rpm momentarily three reps w/o success. Apparently missing something on how to do the burp.  Looked in tech notes etc. but didn't see that issue covered but probably don't know how to access the appropriate info, not having tried to navigate the archives previously.
A marina neighbor who is more knowledgeable is helping me and we'll go at it again tomorrow.
Thanks again!
Bill

[Kyle Ewing]

Earlier this season my M25xp ran warmer than normal (180-190 vs. 160-170).  The fix was to open the fresh water bleed valve (on top of the thermostat housing) until coolant leaked out.  The engine had to warm up enough for the thermostat to open first.  The engine warms up faster in gear so run at fast idle engine speed in forward gear, but only after you check the stretch on your dock lines!

[Bill Asbury]

Thanks, Kyle.  Did open the fresh water bleed valve and eventually a little coolant came out.  Did run engine at 1500 rpm under load with dock lines preventing departure from slip but temp guage needle was fast approaching 220 so shut down.  Did this three times with same result.  Will open bleed valve again tomorrow and continue trying to get air out of system.
Thanks again!
Bill

[Stu Jackson]

Bill, you need to properly BURP the engine's freshwater cooling system.

Here's a story about another issue related to the heating/cooling system: http://c34.org/bbs/index.php/topic,3769.0.html

Just make sure you fill the hot water heater loop and I don't bother to use the thermostat's bleed valve.  If you only use the bleed valve, the engine temp WILL shoot up, stay with it.  Take the HW heater hose off the  bottom of the thermostat and FILL them. (See second picture below)

I also wrote a recent tech notes article published in Mainsheet:


Replacing Antifreeze and Burping Your Engine

A fellow skipper recently asked:  After five seasons I am thinking of changing the antifreeze in my M25. When I did it 5 years ago I recall having trouble removing air after the change. If I slowly drain from the petcock on the block and fill thru the plastic expansion tank simultaneously with the pressure cap off on the engine would this work so I don't introduce air?

I responded:  We just did this the other day when repairing the exhaust riser connection to the flange.  Don't bother with the petcock on the manifold, it's hard to catch the water.

Do this, it's a lot easier.  Loosen the screw on the hose clamp of the big black hose underneath the freshwater pump and use a thin screwdriver to open up the space between the hose and the elbow.  Do it right from the front of the engine. You're right, take off the manifold cap when doing this.

As for the air block, it's called "BURPING" and all you need to do is take the 3/8 inch hose off the bottom of the thermostat.  Pour distilled water or antifreeze or the 50/50 mix into that hose with a funnel until water comes out of the bottom of the thermostat.  Loosen the hose clamp and pull the hose off.  Hold that hose up above the thermostat and pour the stuff into it until the water comes out of the bottom of the thermostat - the nipple that you just removed the hose from.  Once that happens, just put the hose back on the nipple under the thermostat housing and tighten up the hose clamp.  Put some Lanocote on the nipple to make it easier to remove the hose the next time. That gets the air out of the loop of hose that goes to the hot water heater and avoids overheating at startup and does not require that you rev the engine while the thermostat petcock is open.  You won't need to open the thermostat petcock at all.

Update August 7, 2013 - Thanks to Ray Irvine who suggested I add:  "Pour your new coolant into the engine through the radiator cap on the manifold, and not through the small hoses on the T stat.  You only need to burp your engine AFTER the coolant is topped off.  The purpose of burping is to remove the air bubble in the hose from the engine to the hot water heater.  Ray also suggested either holding the hose up high or even adding another short piece of hose to get more "head" on the system as you were burping.  Thanks, Ray.

[Bill Asbury]

Thanks, Stu.  Armed with your info I'll attack the problem again today and let you know how it turned out.  I was also able to access the FAQ: Engine Air Lock, Engine Heating Problem.
Thanks again for your help!
Bill

[Bill Asbury]

Guys, my overheating problem is solved---thanks to your suggestions!  Removed extra hose clamp at HX connection and believe that was culprit restricting coolant flow.  Also disconnected heater hose below thermostat and tried to add coolant but overflowed immediately.  Hot water heater is under galley sink and those hoses weren't drained so don't think there was air in them.  Also opened bleed valve, removed radiator cap, topped up coolant, started engine and ran under load at 1500 and temp guage stopped rising at 160, whereas it previously ran at 170, so I'm happy.
Will take her out for test run to be sure problem is definitely solved.
Thanks again for all your help!
Bill

[Mike Vaccaro]

Another option for burping is to simply open the radiator cap, allow the engine to run and warm with cap off, and then rev the engine to 2800-3000 RPM (when you note the temp increasing above 160 degrees) force the air up and out through the open radiator cap.  It may be necessary to do this two or three times.  This is the method specified in the Universal Engine Manual.  If you don't get the air out of the system after a couple of tries, don't let the temp increase above 200 before you knock-it-off and go to Plan B.

As stated by Stu and the folks in this thread, there are other options as well. 

One other technique is to disconnect the coolant return hose from the heater to the engine (at the thermostat housing) and use a hand pump to pull glycol through the system.  A hand pump attached to the heater return line and run the pump output back into the radiator cap.  Pump the system throughly until you're confident that there is no air.  You'll know right away if there is any air by the way the hand pump behaves as you pull the coolant through the system.  If there is air, you should note the overall coolant level drop in the manifold as well.  You can then top off the coolant and should be good to go.

Cheers,

Mike
 

[Ron Hill]

Mike : I've professed your second solution with a hand pump for many years.
That hand pump is also great for pulling water(prime) up to the raw water pump after changing an impeller or sucking out transmission fluid.  These are but 2 of the many uses I can immediately think of for that handy Par pump. 

[Bill Asbury]

Thanks, Mike & Ron!  BTW, I don't have a Par pump and wonder if it is still on the market?  WM or???
Bill

[Stu Jackson]

Yes, they do.  Beckson's is here:  http://www.defender.com/product.jsp?path=-1|51|299222|84462|315206&id=119228

Jabsco makes one called the "Handy Boy" and a smaller one called "Little Pal" - just take a look at Defender online or their catalog.

[Bill Asbury]

Thanks, Stu!

[mainesail]

I know this is old but thought I'd add another opiton seeing as Stu recently linked to this over on another forum.

This is the easiest way to bleed the system:




I designed this a number of years ago and have installed one on every engine since. The M-25 has a spot for a real ball valve on top of the t-stat housing.

1- Fill the engine as much as you can with antifreeze via the manifold.

2- Do yourself a favor and lose the sub par, burn your fingers, twist and open "pet cock" and replace it with a real ball valve. This one is male X female to reduce the number of fittings. Then connect a hose barb and a three to four foot piece of clear PVC hose. This hose now becomes your engines new "high spot" for both venting and purging air AND topping up with antifreeze..

3- Open the pet cock/ball valve and fire up the engine with the hose held high above it and let her run.

4- As the engine warms and the t-stat opens fluid may rise in the hose. As it drops, when the stat opens, use a transmission fluid funnel connected to the hose to fill it with antifreeze. Eventually the fluid will never dip back into the t-stat cap as the t-stat opens and closes. At that point the system is full and all the air has been purged.

5- Close the valve.

6- To drain any remaining antifreeze in the hose simply dip the hose end into an empty soda bottle to capture what is stuck in the hose after you closed the valve and you're good to go.  Air and antifreeze DON'T mix well, especially if you are using Death Cool (AKA DexCool)...;)