Port engine overheating on a 427 that has been converted from FWC to RWC
New (rebuilt) circ pump.
Pulled t-stat, tested, working fine
Pulled PRV's...good shape and working
The engine will cool if I restrict the water flow coming out of the back of the oil cooler to the PRV's with a vice grips. If I remove the vice grips, no water comes out the top of the t-stat housing and the temp rises.
Good water flow out the top of the PRV's at idle.
The impeller was supposedly replaced 1 year ago, but that was only 25-30 hours on the engine, however I am thinking there might not be enough flow although it looks like the same amount of water through the exhaust on both engines.
From the photo documentation, it looks like you need to pull the pump off the engine to get to the impeller, correct? If so, I doubt the marina changed both impellers last year for a 1 hour labor charge!!
If it's not the impeller, do I have clogged exhaust manifolds?
Hi Trey, haven't heard from you in a while. Had same problem with my starboard with a year old impeller with about 25 hours. Pulled risers (Marine Manifold Corp) thinking to myself it should not be the impeller. It was. Be sure to remover peices of rubber that lodge in front of the oil cooler and double check hose clamps to the raw water pump, I didn't and blew the hose off while on plane. Burnt the paint off the Y collectors from being so hot. Good luck
I suppose someone in their younger gymnastic years could do this impeller change-out with the pump still on the motor, but it would take standing on your head for a while in a very uncomfortable position on my 38 Express. Maybe other boats have better access to this equipment. If you’re going to do the job right and look inside, inspect things, you’ll need to pull the pump out and get it on a bench.
A look inside a Sherwood sea water pump. This photo shows the replacable cam, which is what actually creates the suction on a pump of this design. These things can eventually wear down to the point where they produce less suction, even if the impeller is new. I think they're about $35, and still available, which is pretty amazing.
Thanks Paul, sounds like a worn cam could be the problem....
If I am going to pull the pump, I may as well be prepared to replace the cam along with the impeller. Is it going to be a 2 weekend job? i.e first weekend pull the pump to get the pump number, find the parts, order parts, receive the parts, second weekend install the pump. Or are the parts readily available at a local marine shop?
Probably don't need the cam, it's probably the part that wears out the fastest (impeller)
January 17 2008, 7:13 AM
Trey,
The links I've posted have charts and you can even see the ID numbers stamped on the pump housing itself. Since these were used on the small and big block motors, there are a lot of them around.
I think it depends where you are, regarding availability. Here in Tennessee, I think I can call Marysville Marine and just drive out and pick up an impeller. I think the cams have to be ordered from Sherwood. The impeller is probably all you really need. If you run in sandy or silty water, those pumps get more wear than they do out in that pretty blue water in Lake St. Clair, for instance.
I have changed out several of these over the years, and I think I actually did one without pulling the pump out. If you do this, you better be in good shape, because it's tough to get back out of the engine room when you've been standing on your head.
From the beginnig my Starboard engine was running hot, probally due to a bad heat exchanger, I did replace the cam I purchased from Depco Pump, there are several sizes with varying gpm. I steped up one size. I did do a test by teeing hose to the raw water out flow out of the heat exchanger and dumped it into a 5 gallon bucket. I ran each engine and and marked the amount of water. Starboard did produce more water. Its impellor failed with few hours. Next time I get warm I will go straight to the impellor.
Well, the pump came out easily to my surprise, not a bad job at all. Unfortunately, the impeller and cam looked to be in good shape. I will say the impeller was cold and the blades that were compressed againt the cam did not spring back at all until the pump warmed up in my truck on the trip home, but once home, I pulled the impeller and it seemed soft and plyable. I will obviously replace it with a new one anyway, but I think I will be back at the drawing board for the overheating problem.
Would there be any harm in restricting the water flow out the top of th PRV's into the risers? This would make the sytem pressurize more and force the PRV's to open to provide water to the risers before the t-stat opens and lets water out the top of the t-stat housing to the risers. Just a thought......
I re-read your note about restricting the PRV hoses with vise grips and the motor would cool itself. I am assuming this is during the cruising speed, and not the idle speed.
The PRV is intended to bleed off excess pressure when the engine speed goes up. It also is intended to close down flow to the risers and divert all the cool water into the motor first, before being ejected out the tail pipe. If you restrict flow to the PRV system, then you are forcing more water and pressure into the motor at higher speed. Personally, I don't think the additional pressure would hurt, but I'm beginning to wonder about hose size and the conditions of your conversion to Raw Water Cooling (or as CC says, Standard Cooling).
In your conversion, do you have a " T " or an " L " right off the sea water pump?
Thanks Paul. The "vice grip" solution was at idle, not cruising. My PRV's have one inlet and 2 exits. One exit is an unrestricted bypass out the top that goes straight to the risers, these are the hoses I can clamp and get engine cooling at idle as there a lot of flow there. The second outlet is through the PRV valve and also exits to the risers (no hoses here, threaded directly into the risers).
My current config is as follows:
From the RW pump there is a "T". Down is a 1 1/4" hose that goes back to the oil cooler and from there at 1 1/4 to a "T" and on to the PRV housings described above.
The top of the "T" out of the RW pump is reduced to 1" and goes up the the engine circ pump on one side only, the other side of the circ pump is capped. From there the circ pump pumps to the manifolds, then I assume through the enigine and intake, then to the T-stat. Then, when the t-stat opens, it looks like the water should come out the top of the t-stat housing to another "T" and dumps back to the risers (a 3rd source of water to the risrs).
Both engines are done exactly the same and there have been no cooling issues until now.
Put the RW pump w/ a new impeller in this morning. Temperature went high again...dammit! I went back to the idling engine to check for water coming out of the top of the t-stat housing, and there was some, then none, then some. The t-stat is opening and closing and there is plenty of water behind it. Went back to the helm and caught the temp guage coming down from 205 or so, stopped at 195 and started going back up. I know the t-stat is opening at 160 because I checked it in a pot of water with a thermometer. Hmmmmmm. Shut her down and swithced sending units from the other engine. Start up and still hot! No way, I thought to myself as I move the sending wire from the port guage to starboard. Start her up again and cool as a cucumber....160!! Sure enough, bad temp guage and it's less than 5 years old and stays dry. If it were not for twin engines, I would be pulling manifolds and risers this afternoon.
I was wondering about swapping out the sending units and or the wiring to the gauge. There are two kinds of sending units, those for dual station and those for singles, but that didn't seem to play into your scenario.
Rust and scale internal clogging is possible with old iron
September 2 2008, 9:45 AM
Well this thread is a good one for overheating diagnostics, but the cause of this particular problem was a faulty gauge and not actual overheating.
In the event of true overheating, the cause can be all of the above noted issues, and it can also be rust and scale accumulation. Salt water risers can be literally EATEN UP and look like they are coming apart like the pages of a book. Fresh water iron lasts longer, but take a look at this riser end, and you can see rust and scale buildup, and it can restrict flow.
The work involved to clean out exhaust logs is a basic wrench turning and pumping iron session, one heck of a physical workout. Here is a thread showing some small block manifolds and risers coming apart for inspection and cleaning. The 427 or 454 big block manifolds are the same, only heavier. Taking an extended length of coat hanger wire and fishing it down the passage-ways can do wonders in loosening any scale or rust. These parts can also be "boiled out" at your local radiator shop too if you really want to haul the stuff around.
It's safe to say, some of our motors may have the ORIGINAL MANIFOLDS on them, and they may have never been taken off the boat. If so, those old pieces of iron may well have sediment from internal flaking and scaling.
