CC V8 pressure relief valves (low speed overheating)

[Paul P]

[edited moved image to postimageserver]
ABOVE: A grungy CC pressure relief valve that may not have seen any attention in 20, 30, or 40 years. This particular one was being held open by a piece of substance that looked like a little bit of charcoal, and it was short circuiting my cooling system by dumping needed low speed water right out the riser (causing the motor to overheat). This motor had not been run in six years. It is now running beautifully and ready for the 2007 season. The PRV is just one more thing that can go wrong if given the chance. A little preventative maintenance goes a long way.


The other day as I was working on my latest restoration project, I discovered something I want to pass on to everyone out there running the 283F, 327F, and similar motors of newer vintage such as the Q series small blocks, as well as the CC 427. There are many such motors installed in wood runabouts, so I think this issue can be of interest to many.

I hooked up a water source to my 327F the other day, fired up the motor, and the exhaust manifolds were overheating. I shut things off, ran the hose some more, took off some of the fittings, and I discovered water was not reaching all parts of the motor. Why?

Well here's why on the 327F, and this may well apply to many of our CC motors. The 327 is tilted with the forward part of the motor higher than the prop shaft side, like most of our motors are. A buddy's is tilted the opposite direction, but he's running a V-drive, but the same issue will apply.

Water runs uphill only when it's pressurized, and of course it's pressurized when using a garden hose, but I do this very carefully so as to not overpressurize a motor (few are able to stand full city water pressure). For some reason I couldn't make water run uphill to the front of the motor by using the impeller on the motor, but when I was test running the motor I could see a lot of water coming out the tailpipes. I was puzzled (for a minute or two).

Since I knew the water was making its way to the tailpipes, I decided to take a look at those pressure regulators at the back of the motor, in this case they are attached to the risers. Sure enough, BOTH were stuck open, due to debris. One looked like it had a little twig holding it open, and the other had a bit of debris I couldn't identify. I took both apart, ran a screwdriver around the parts that touch, and cleaned em out. This time when I put things back, those valves kept water from immediately draining out of the back of the motor, and allowed the water under pressure from the hose and water impeller, to reach the front top side of the motor.

With those pressure regulator valves being held open, the water took the path of least resistance, and it drained immediately out the back of the motor.

If anyone has LOW SPEED OVERHEATING, a pair of stuck open pressure regulator valves could well be all of or part of the problem.

When you're under idle conditions, those valves cause almost ALL of the water to go through the motor. When engine speed increases and the pressure builds up inside the motor, they open up and allow water to be wasted right into the riser. If these guys are stuck open, you may be able to run well at speed, but when you slow down your motor may be starved of water, and looking at the tailpipes could be very misleading because you'll still have water coming out (but it will be short circuited, as your motor is cooking).

I later took these off the motor and more thoroughly cleaned them up. Here is a thread with lots of large resolution photos for reference.
http://www.network54.com/Forum/424840/thread/1164411296

In addition to the pressure relief valve causing a potential low speed overheating, of course it can be your impeller too. It can also be your Sherwood Brass sea water pump CAM. Some people may not realize there is a replacable cam inside the Sherwood pumps, and even with a new impeller, if that cam is worn down due to running in silt or sand, or just plain running a long time, then your water flow can be reduced. These are still available for around 35 bucks, and a buddy of mine who replaced his reported "much more water flow".



ABOVE: The cam on a Sherwood Brass sea water pump is that curved metal piece inside the pump, that is touching the impeller blades.


Along with the PRV, impeller, cam (and associated side wear plates), internal obstructions can reduce flow too, and this is most often observed at the transmission heat exchanger because it's in the inflow circuit of water to your motor.

Happy (cool) running !

Regards, Paul

[Bill Basler]

Paul, I have seen this exact same problem a number of times on thermostats onraw water cooled systems.

When we boat on Lake Michigan, we are typically in water that is 20-foot or deeper. Most of the areas that we cruise are 150-200 foot of water. Even island hoping means anchoring in about 6-10 foot as the shorelines are nearly all rocky. Sucking up stuff from the bottom is not really an issue—as if you are that close to the bottom, you generally have bigger problems.

Mississippi River cruising is another ballgame. Often the river depth is12-20 foot in the channel, tapering to 3-4 foot in some of the desireable anchorages. On a modern day I/O this means trimming up, keeping an eye on the depth finder and watching the engine temp gauge.

Just this last summer, after anchoring for a few hours in skinny water, we had to back down to get back into deeper water. This often leads to the problem you describe. After getting a snoot full of sand and bottom gunk, it was a bit tedious to get going again and to get the engine to spit out the undesirable stuff. After a few minutes of starting—revving—and shutting down when the temp starts to climb, we finally got the obstructions to clear, only to find after about an hour of running the engine was running cold.

In the shop we pulled the impeller which was due for a change anyway. We then pulled the thermostat to find a small pebble lodged just so, keeping the mechansim jammed open. It essentially defeats the purpose of the thermostat as it cannot close when needed.

[Paul P]

Hi Bill,

The mention about the thermostat is right on target. They are similar in valve function to the PRV and they can be held open with debris. As you noted, when this happens, the motor tends to run cold. While these parts can cause problems, they're actually pretty darn reliable. A little preventative maintenance in the off season will go a long way.

I think the "silt factor" that you mention is worth commenting on again. Where I run my 1966 38' Commander on the Cumberland River, we're a uniform depth of around 30 feet because it is actually a "run of the river lake" with no flood capacity, and the locks are there for commercial shipping purposes. However, in our harbor and at picnic anchorages around, sometimes when I put those big 23x25 props in reverse, I can see a coloration in the water being pushed out in front of the helm station, and I know the motors may be sucking that junk in. Therefore I naturally try to avoid that situation.

Our silt factor is relatively low, when compared to the Ohio or Mississippi. In those waters I think the motors probably do okay, but those brass wearing surfaces on the pumps must have a higher wear factor. Anyone running in those waters over a long term, might do well to take a look at the wear on their Sherwood cam when they replace their impellers. Of particular note, I discovered the Sherwood pump normally found on the 427 motor, the S11095G, is also listed as a replacement pump for the 293F and 327F, and the Sherwood D05 pump on the 327Q takes the same impeller. Anyone should verify parts with their specific pump # before ordering.

The older styls Sherwood M10095G style pumps (those with the two impellers inside the single housing, with two intake and two outlet ports) also have a replacable cam. Here is a photo (below) of one of those old style pumps, which I have on an early CC V8 that does not have any pressure relief valves or thermostats. One of the two impellers is out, and there is a wear plate between the impellers so you can't see the second impeller in the photo.


ABOVE: Sherwood Brass M10095G dual impeller pump as furnished on early 283 flywheel forward motors.

Why Sherwood thought they needed a pump with two complete circuits is beyond me, it's the craziest looking thing, but I guess you have a little redundancy that might help get you home? This was one of their first pumps for a small block V8 motor. I'm curious if some of the older Caddilac motors used a similar design. One thing about all Sherwood pumps, they're good old fashioned American Quality, built heavy, and built so they can be repaired with replacement kits. They probably used twice as much brass in these pumps as some of the new ones have!

Regards,

Paul Pletcher

[Bill Basler]

Good stuff Paul, and thanks for the pictures. It's amazing that you had the foresight to photograph things as you go. I am back into working on my barrelback and a new project boat, a 1936 Gar W*&d utility. I am trying to document everything as I disassemble. I have put my camera inside of a huge Zip Loc bag with only the lens poking our through a small hole. At times it is hard to take pictures while removing a greasy old gas tank. Hmmmm, maybe I shoulld have my wife take out the gas tank, while I direct and take pictures. I may try that.

Not to beat a dead horse, but on one particular boat that I owned, I ran seasonally on Lake Michigan for the better part of 10 years logging hundreds of hours. This boat was an I/O and after 10 years, only the paint on the very leading edge of the skeg was starting to fail. The stainless steel prop shined like showroom new.

Another boat that we owned, we kept down here for river cruising. After half a season the skeg was sandblasted down to bare aluminum, and the prop had a very matte scoured look to it. Generally speaking the stuff is cosmetic.

The biggest problem with sand is that it wants to move under the pressure of the fresh water cooling. But once it settles into every nook and cranny, it is very hard to get it moving again. On our boats that see a fair amount of river action, we pull the water pumps, pull the thermostats, and get into every opening possible with a garden hose with a high pressure nozzle. It is amazing what you'll get out. If you can get the sand moving, it will usually stay moving and it will cooperate.

With the raw water pickup on the hull bottoms of our old Chris runabouts, it's of course wise to consider what type of water you are running in. It can make a huge difference in the type of maintenance you do.

[wheelsnkeels]

Does anyone have a spec on how many pounds of pressure the sea water pump is supposed to put out?

I took the small hose off the riser and then started the engine. I had significant flow after about 15 seconds. When placing your thumb on the outlet the pressure is higher on the starboard engine than the port.

I plan on changing both impellers in the spring but was curious if there was a spec I could guage.

[Paul P]

It always helps to identify the motor being discussed, but with this vintage Catalina, I'm thinking you're running a pair of 327Q or 350Q motors. I am not aware of any ready source of pressure, but the GPM rating of the pumps should be out there somewhere.

The important issues are a free and clear intake passage from hull scoop through the strainer to the pump, good pump mechanics (housing, impeller, cam), and good hoses and connections to keep out air. Any air in the system potentially makes it harder for the pump to prime, thus the 15 second delay. This is also a symptom of worn impellers or cams too. If you remove the pumps and pop them open, you may be able to see some wear issues.

The greatest assurance is to add new impellers and that should generally do the job. If you see what looks like a lot of internal wear, you may want to add the replacement cam too, because that increases the suction the pump is able to achieve. I'd open the pumps, take a look, and then look at the (Sherwood?) rebuild kits that are available. That will identify the wearing parts that generally require attention.

Some of the Q motors (and 454 series) had an air pocket problem unless the system was set up properly.

I'll have to hunt for the info because I'm running on memory now and I don't own a Q motor. If I find anything I'll post it here on the thread.

Regards,

Paul

[Paul P]

Hey, look what I found ! Hope this helps.

Regards,

Paul

[Wood Commander]

Paul, those Q's have a really convoluted cooling system don't they? Even without the closed cooling option.

I have a 307 Q with raw water cooling in my Lancer. I am going to build a new engine and am accumulating the parts to turn it into an "F" setup (I have several reasons for wanting to do this and Lancers like this were equipped with either setup), but I will be using Mercruiser- type exhaust manifolds and risers and going to through- hull exhaust pipes. When I hybrid the plumbing between the Chris Craft F and Mercruiser, do you think it would be advantageous to install these pressure relief valves into the Mercruiser risers?

[Wood Commander]

Oh and I forgot, it's great to have all of the great info and pictures that you provide for us! Thanks Paul!

[Paul P]

Hi Bret,

It's my pleasure to share info I may have. I appreciate all the info I've received here on this forum, Bill Basler and all of the other participants here are doing a fine job.

Regarding that re-engineering job you are contemplating, I have a buddy who is a mechanical engineer, and here is the system he used. It used a Volvo Penta heat exchanger setup, etc., and I don't know if he used the pressure reducing valves or not. Without the PRV, the internal pressure on the motor may reach unacceptable levels, I don't know. It is for this reason some people caution about hooking a Model K, for instance, up to a garden hose, becuase house pressure of 60-pounds is way in excess of what a K is supposed to take. The PRV just "wastes" water directly into the exhaust at high speed pressures.





These motors belong to Mike Burdette, and you can see he has been pretty meticulous with the installation. THe boat is a 31' Commander Sports Express (fiberglass) that he is restoring from the keel up. The boat looks marvelous, by the way.

Whether or not his system will outperform what CC engineered, remains to be seen. I like those big heat exchangers, however, and I think the ones SenDure used on the mid 1960s CC motors (especially the 427) were a little undersized, because I have heard of so many overheating issues. Since overheating can result from numerous causes, like air in the pump circuit, bad impeller, bad cam inside the pump, obstructions at the transmission oil cooler, blocked PRV, whatever, maybe the heat exchangers themselves have gotten a bad rap. In any case, bigger seems to be better in this case.

I think its possible for the backyard mechanic to out-engineer Chris Craft, but the probabilities may not be too good. Proceed with caution like Mike did, I'm sure you will do well.

Regards, thanks for the comments,

Paul

[wheelsnkeels]

Thanks Paul
The boat is back in the water again. Now I am back to chasing the overheat issue on my port 350Q with closed cooling. last season I cleaned the PRV's thank you very much. I have verified the sea water pump is working properly. Today I dissasembled the heat exchanger and back flushed it. It had some rust in it but nothing earth shattering. I cannot sea trial it yet as it is too windy today but will test probably tomorrow.

The boat runs fine from idle to 2700rpm maintaining approximately 145 degrees. When you bring her to 3000 rpm she slowly climbs to above 160 degrees. If you persist she keeps heating up. If you back down to 2200 for a while she cools right back down. The starbord engine never rises above 145 the whole time.

With the cap off I can see flow from the circulating pump after the thermostat opens. Perhaps it may not be opening fully. I will pull the thermostat tomorrow if it still heats up.

[Paul P]

Okay, you seem to have eliminated the low speed circuit, and now you need to look at belts and pumps. If there is an air leak in the system you can have problems, naturally if the pumping volume is down you will not be able to bleed off as much heat, and the impeller, belt, and cam are now on the suspect list.

Are both exhaust outlets putting out the same amount of water? Have you taken a pyrometer over the system and compared one motor to another? That sometimes gives a bit of info. The heat exchanger itself, is sometimes obstructed too.

Thermostat is also in the loop. These do go bad from time to time, and they also get a bit of debris lodged in them too. The only way I know to find the problem is to start the process of elimination.

Good luck, let us help you if we can.

Regards,

Paul

[river rat 1939]

hello paul i have a 30' constallation
with 283 fly wheel forward motors . where can i find the impellers for the older style pumps you talked about also the cams and thermostats for these.one pump has the fin type impellers the other has the round type impellers. any help would be great !!!!!!!

thanks steve

[wheelsnkeels]

Hi Paul,
Yes the Low speed circuit is fine and she is reliable to 2700 RPM.

Checked Thermostat today and its missing so she should be cooler but isnt.

Cleaned Heat exchanger yesterday no luck.ran at speed and bled the line from the manifod to the intake to remove possible air - no fix

The flow from both motors seems equal at speed.

I will borrow an Infrared thermometer from the neighbor when he gets home from work. then I can compare different points on the engines.

I am starting to suspect a bad circulating pump on the engine block for the closed system, but it still could be a blockage in the system somewhere.

I'll keep you posted!
Mark

[evansjw44]

I had a inlet hose that collapsed internally which would block flow. The hose looked OK but it collapsed internall under vacuum.

For what its worth.

[Chris Hall]

I have a 283 on my 1959 Continental---I don't see any obvious place for a pressure relief valve or a thermostat. Do they exist on these motors?

[evansjw44]

Your engine doesn't have one. Your engine has what amounts to two independent cooling systems, one for each side of the engine. That's why it has a double chamber water pump. That design lasted through roughly 1964 when CC went to a cooling system with a circulating pump in addition to the raw water pump.

I beleive all the 327s had the later cooling system and at some point the 283s were revised as well.

[Paul P]

Here's a bit of info on that old style 4-port Sherwood.

The dual impeller Sherwood pump shown in Chris Hall's fine image has two outlet ports, with one circuit going to each exhaust manifold where the water is pre-heated at the hottest point of the motor. From there each manifold dumps into the block where the water is mixed, with mixed water eventually being ejected out each manifold.


Replacement pumps with a T splitter do the same exact thing with one impeller. Why CC thought the dual impeller pump was viable is sort of a puzzle to me, although if one impeller went out the other one would potentially keep pumping water through the (almost) entire system.

That big round engine lifting ring on the top of Chris's motor is the place for a thermostat housing. There are numerous kits available for this installation and they're simple to install. THey basically meter recirculated hot water to maintain a more constant engine temp.

Here is a rather poor photo showing one such T-stat kit being installed at the lifting ring hole on an identical motor. This particular motor was fitted with an aftermarket single impeller pump to handle what I believed was an additional cooling load, and it has a T-fitting to send water to the original inlet locations.






regards,

Paul