Engine overheating

[Exodus]

I just replaced my circulation pump because the bearings had gone bad.  While I was at it I replaced a couple of the hoses, changed the zinc in the heat exchanger.  I also checked the impeller (was okay).  I put everything back together with new gaskets, painted the engine and added more coolant.

Then started the engine and it overheated.  Everything looks okay, no leaks, I topped the coolant off again and tried again, but the engine overheated again.

Any suggestions on what to try next?

[Stu Jackson]

Yes, simple.  You need to BURP the engine, covered in the Critical Upgrades sticky topic.

[Exodus]

Thanks Stu!  I thought I had done a thorough search, but apparently not.

Anyway FWIW my engine appears to run cooler now than it did before.  Seems to stay around 170-175 now where as it used to stay at about 180 before I replaced the pump.

[Indian Falls]

I heard this on the radio program Car Talk with Tom and Ray Magliozzi:

When they service the coolant system on a car they put an asprin in the thermostat to hold it open.
Once the engine is started the pump is free to push water with ease through the system before things get hot. 

About the impellor:  I found half a dozen broken off fingers from impellors in my heat exchanger.
I also found that if you install the impellor with a finger bent forward, leaning in the opposite direction of rotation, which is really easy to do, it will stay that way.  I think this contributes greatly to the reason I find these fingers down stream.  When I replaced the impellor for the first time it came out and fingers were literally bent in all directions.  I also pulled this new impellor at sea after an overheat and found that I'd gotten a finger bent in the wrong direction, upon removing the cover it was still leaning forward. ( the overheat was from a low coolant level)
It takes a lot of fooling around to keep them bent back and align the keyway but I can do it.

Just wondering if you saw this too or if anybody thinks this is nonsense.

[Ron Hill]

Dan : The "tappet brothers" use the aspirin because most auto engines do not have a bleed valve on the top of the thermostate like ours does. We don't have to open the thermostate housing.

On the installation of the impeller - the direction of the installed blades really doesn't matter.  There is an eccentric piece (bottom left inside on an Oberdoffer) that will cause the blades to straighten out to the direction of rotation.  You should place a thin coating of grease on the inside cavity walls to assist with the prime and to lube the impeller till the water does that task.

A few thoughts

[Ted Pounds]

I read (and posted a while ago) that the pink anti-freeze is hard on rubber, including impellers.  After I read that I always removed and cleaned my impeller after winterizing.  They seemed to last longer that way...

[Ron Hill]

Guys : To expand on what Ted mentioned :

Just remove the the entire impeller (on shaft ), dry it off and spray it with silicone (to keep it limber) and set it in a plastic cup under the engine till spring.  I also removed the Zn which completely drained the heat exchanger.  The "antifreeze" for the engine winterizing was only left in the muffler (which is too nasty to drain)!!

A thought

[mtullier]

One other thing to keep in mind is that a 50/50 blend of AF to H20 should be used.  Pure antifreeze does not remove as much heat as the 50/50 blend.

[Indian Falls]

Ron, mine is a Sherwood...

That's what I'm saying though...   the impellor fingers are not straightening out.  The one I removed when I got the boat had fingers pointing in all directions.  I put in a new one and about an hour run time later pulled it looking for an overheat issue and found 2 fingers still leaning in the wrong direction.  If you put the impellor in the housing and turn the engine with you hand they don't right themselves. If watch one approach the cam they lean forward and get folded in half rather than lean back and bending over.  This is why I'm presuming they break off and end up in the HX and also why I take the extra time to fiddle with it until it goes in with all the fingers leaning back.  I'm just waiting to see how long it takes before I find some fingers missing on mine.

When members open up the impellor for service or winterizing it would be great to get feedback on the condition of the fingers and post it here or whatever.  I'm thinking that no one really pays attention to this and just stuffs in there like I did the first time.

[Stu Jackson]

Even though I have heard, many times, that the pump "fixes" the blades, I made a sketch in my log book as to what direction they should be in.  That said, there have been times when I don't pre-bend them.  When I replace them, the blades are all in the right direction.  We have an Oberdorfer.

[Ron Hill]

Dan : If the blades are limber, they should automatically be bent in the correct position. 

I have a Sherwood on my new engine and as I recall the blade ends are bent back to starboard and the rotation is clockwise (looking aft at the engine at the top of the pump). 

[Ken Juul]

The blades should self align.  However if you want to install with the correct bend in the blades, manually fold the blades in the correct direction.  Use a zip tie to hold the blades in position.  Slide the impellor partway into the housing (Oberdorfer) or slide the housing over the impellor (Sherwood).  This should push the ziptie to the end of the impellor.  Cut and remove the ziptie when enough of the impellor is in the housing to hold the shape.

I usually use cooking oil to lube the vanes as some greases will damage the rubber.

[Ted Pounds]

I always used Vaseline for the same reason Ken uses cooking oil...

[Mark Sutherland]

Exodus:  My (1986)engine was running 180 when I bought it.  I demineralized the raw water system with 20% Ascylic(?) acid, and flushed the fresh water system with Zerex Radiator Super Cleaner.  My engine has run at about 165 ever since.   I have instructions on how to do it if you're interested.

[Stu Jackson]

Mark, what temperature thermostat do you have?  One would assume a 160F.  Ron Hill has reported success using Rydlime (sp?).  I have recommended that a real servicing of the HX requires its removal for two reasons:  1) the entering port from the raw water  pump can get clogged with salt deposits (if you're in that environment); 2) depending on how your HX is mounted, you should check for chafe on the shell where it meets the bracket.  It's not too hard to do once every few years.  When I was checking my zinc last month I found the bracket on M25 had broken! 

Whether you run a material through the HX for the tube cleaning, or whether you take it off and do so, doesn't matter.  FWIW, in 13 years I have never had "tube" issues.  I replaced our old 2" HX with a 3" one in 2003.