There have been a lot of threads here on The Forum about overheating, and most of the causes are well known and well documented. Issues like rubber impellers needing replacement, cams in the old Sherwood pumps being so worn they don't create the necessary suction any more (replacement cams for these pumps are available for $35), air getting into the system which causes loss of pumping capability, internal blockage, bad circulator pumps, thermostats, corroded heat exchangersetc. I have heard about using muratic acid to clean out the oil cooler and quite frankly, I think this is dangerous and unnecessary except for extreme situations. However, there are some other things that can cause a motor to overheat, which are not discussed very often.

There can also be a clogged oil cooler, which on some motors (closed versus standard cooling) will make more of an impact than others, take a look at the diagrams here and you can see why. The pressure regulator valves are well documented here on The Forum too, and they help assure you get FULL WATER to the standard cooled motor when your boat is running at idle speed, and they help bleed off excess pressure at high rpm. If the PRV is stuck open on the stancard cooling system, then you'll overheat at low rpm. On the closed cooling system (see diagram) the PRV system seems to only function as an emergency pressure relief device, and the closed system, you'll note the clogged oil cooler can affect the entire cooling flow to the heat exchanger. Exhaust lines and exhaust manifold internal passages can become clogged, causing a short circuit in the system, which can lead to overheating.

Now.................for four things that can also lead to overheating, which are seldom discussed:

1. Late ignition timing.
2. Valve lash in need of adjustment.
3. Collapsed water pump suction hose; this one can be tough, because sometimes the hose fails on the inside and it is not visible on the outside. Your motor may run fine at low rpm, but the internal hose structure can be sucking in as rpm increases, causing a higher rpm starvation right when you need more water.

4. And on those freshly rebuilt motors, a wrong rotation circulating pump installed on a motor that is intended to spin in the opposite way. The 427 circulating pump is rotation specific. This means a RH pump is REQUIRED for a RH motor. You can bolt a LH pump to a RH motor and it might pump a little water, but I think it is safe to say you'll have overheating problems. Here is a thread with photos of the 427 circulating pump, and its directional cast bronze impeller.
http://www.network54.com/Forum/424840/message/1182358080









In case anyone is looking forward to standing on their head in the bilge, going after that sea water pump and changing out the rubber impeller, here is a great thread here on The Forum showing the internals and how to do it. http://www.network54.com/Forum/424840/message/1156595176.

Regards,

Paul

I got two emails allready this afternoon regarding the PRV and this is the most efficient way to communicate the info, and to share it with others who may (also) be interested.

Here is that link on the Pressure Regulator Valve

http://www.network54.com/Forum/424840/message/1164411296



You can see from the photo above how simple this device is. It is all yellow metal and there is nothing to rust. These can stick (one at a time) in the open position, in which case you will see a lot of water coming out of one side and less from the other. If this happens to a hot motor that has just run across the lake and you idle down, you will be dumping precious cooling water right out the exhaust pipe without sending it through your nice and hot motor, and in some cases it can be bad enough to cook the motor.

It is spring loaded, and intended to be CLOSED while idling. As engine speed (and pressure in the cooling system) increases, the abundance of pressure will need to be regulated, and the spring allows the EXCESS water to dump right out the exhaust system. When working properly this simple device works very well.

On the closed cooling systems (those using antifreeze) the PRV is of very little value, and may serve a purpose we don't yet know about. On those systems it appears to be more of a pure regulator device for overpressure than it is a diverter of cooling water to the system. For some reason CC decided they did not want too much pressure in the system, perhaps to protect from leakage into the motor through gaskets, etc., and this device will do that job. Since many a closed cooling system has experienced overheating from the marginal heat exchanger many Commanders have, this device on one of those systems just seems to be there to assure a pre-determined minimum water pressure on the heat exchanger, since many of those systems get the full flow through the exchanger whether the PRV is workig properly or not. Study the diagram in the prev posting and you'll see what I mean.

The standard cooling systems appear to work perfectly in anything other than really warm tropical water. In these same conditions, the closed systems will be getting hot just about any way you look at it.

This PRV is installed on small and big blocks alike, either directly to the riser as in the photo, or on a detatched case hooked to the riser via rubber hose.

Regards,

Paul

Good morning Paul,

I found this posting to be very worthy of printing for my three ring binder, as it is a great reminder of the various things that should be checked for a trouble free season. Looking at the diagram, it seems to me that adding another heat exchanger (two per motor) would go a long way to giving the system the capability to handle just about anything. There are so many of these SenDure heat exchangers out there sitting around, they should be available for a song. Plumbing one up to feed through the other one would appear to give the system plenty of time to grab heat and remove it from the motor. I am curious if anyone has fitted a 427 motor with double heat exchangers, salt or fresh water, and if so how has this worked?

James

Good morning back to you, James,

Stock closed cooling system:



The idea of double heat exchangers (or larger exchangers) has been discussed in the past. The CC system (in my humble opinion) can be easily upgraded to handle warm tropical waters by going to such a system and in the past my thinking would be to simply upgrade to a very large capacity heat exchanger and open the flow pathway from the sea water pump so it produced all the volume it was capable of. That way, if the capacity was over-sized (as in large aluminum racing radiator in a car that didn’t really need all that big a capacity) the thermostat would be the controlling factor and would keep engine temp right where it needed to be ALL THE TIME.

Too bad Chris Craft didn’t order up a larger heat exchanger, it would have kept untold people from thousands of hours of aggravation. As for the plumbing of two units together (in line), yes, that would be a simple plumbing exercise where the first unit took out some of the heat and the second unit took out the rest. I think it would make a huge difference for people who are in Florida waters, for instance, where the water temperature gets up to 80 degrees, and sometimes maybe higher.

Here is a copy of my re-engineering job on the basic CC closed cooling system. This would be the “simple” addition of a second heat exchanger, leaving the somewhat restrictive pathway of cooling water as Chris Craft engineered it, through the oil cooler first.



If I were going to do this to my boat, I would consider plumbing that oil cooler into a secondary pathway, just exactly like the standard CC cooling system uses (“standard” being the CC term for the fresh water system that does not use antifreeze). I don’t like the fact that the oil cooler is restricting flow to the entire motor, but with a second heat exchanger to transfer more heat with the same basic flow Chris Craft engineered into the boat, I think this (as modified in the diagram) would work great. Naturally, it’s easier to draw the schematic than it is to do the work.



In addition to the above, here is a previous thread which is a couple years old, exploring the shortcomings of the 427 closed cooling system.
http://www.network54.com/Forum/424840/message/1125601029

Hope this helps the guys in tropical waters, who are experiencing overheating with their stock closed cooling systems. Depending upon how tropical you may be, this might be a solution to overheating issues. With twice the internal surface area for heat transfer, this has got to be better than what came on the boat originally.


Here (below) is a variation on the theme. While this one looks more complicated, it may be more simple to install, using "T" sections to simply splice into existing hoses. This one has the benefit of cold water supply to each heat exchanger. There are other variations on the theme, and I think there are more than one solution. Certainly installing one larger exchanger would probably do the job too.




Regards,

Paul

Paul,

I love the diagrams. I see little fault in your approach, and I agree having twice the internal surface area for heat exchange would do wonders for some of the guys who have to run the antifreeze systems. Cost being no object, I would go for one extra large heat exchanger with a dedicated feed line, and I would run the oil cooler on that secondary circuit as you suggested. The comment about a lot of the SenDure CC heat exchangers laying around is probably true. It probably would not be all that much trouble to graft on another one. It would be very intresting to do one, and run the boat and compare one side to the other regarding temperature, warm up, ability to control heat, etx.

Tom