Riser (elbow) temperature

[saf]

No bubbles. That was the first thing I tested, definitely no air leaks, neither stationary nor on the plain.

I did not back-flush the raw water pickup line yet. Could not figure out how to do it. I'd need an adapter from a garden hose (the only thing I have with some pressure in it) to 1-1/4" barb, which I don't have. Even then, the garden hose is much smaller, I am not sure it can create strong enough back flow. Besides, with vacuum reading being low (not enough vacuum in the pickup line) I thought the pickup line blockage is unlikely. In any case, I am ordering a 1-1/4 ID reinforced hose with a 1-1/4x1' barb adapter to bypass the pickup line from the oil cooler to the pump. We'll see...

I am contemplating another test. I want to hook up a garden hose to each manifold and measure the flow rate. Any idea what kind of flow I should be seeing?

I do not think this is a pump problem. The riser overheating problem was there with the old pump as well. (the old pump developed a leak, leading to its replacement, but was running fine with a new impeller)

 

[Scott Danforth]

go to your local Lowes or Home depot.

they have a plastic 3/4" to 1-1/4" adapter for a few bucks and a 3/4" to hose adapter for a few bucks. add two hose clamps for a buck and a foot of 3/4" hose for $2 and you have an adapter you can put into the line to backflush the power steering cooler and the hose. (the power steering cooler will be the first "strainer" in the system)

add a section of 1-1/4" hose to your adapter and you can feed the raw water pump directly to run on a hose vs the muffs.

conversely, you can take the male end of the garden hose and shove it inside the 1-1/4" hose and use a zip tie as a hose clamp to backflush. wrap a rag around it to minimize any residual spraying in the bilge

 

[saf]

An update: I think I narrowed it down to the heat exchanger. As I mentioned before, I am getting overly high back pressure in the raw water system after the pump (15psi@3000rpm). I bypassed the heat exchanger by connecting the pump directly to exhaust manifolds (via 1"x3/4"x3/4" splitter) while cooling the exchanger through external water supply, the pressure dropped to where it should be (2-5psi). So, it's gotta be the heat exchanger... however, I still see nothing wrong with it, looks totally clean. Is it possible that this is a wrong size exchanger? Any ideas? I am getting really desperate here...

 

[Lou C]

Why not post up some pix of your system and take measurements of the heat exchanger?

 

[ripjmk]

I don't know what exchanger you have but it sounds like you have either the end plate gaskets in the wromg orientation or on the wrong end! Check the flow path through all the passes. It is probably a 4 pass exchager check the end plates allow flow from one pass to the next and flow all the way through to the outlet.

 

[saf]

Here are a bunch of pics of the engine and cooling system, not sure how useful these are, let me know if you want to see something in particular. The heat exchanger is 14" long, 4" in diameter.

Did another series of tests this weekend, and it looks like I am back to square one:

1. I bypassed the heat exchanger (again) and measured the water flow (as a reminder, last time I determined that the heat exchanger was creating excessive back pressure). To my huge disappointment the flow rate increased only 10%, I am still getting ~18Gpm in-situ @3000rpm. Furthermore, I spoke with nice people from mrcool.us who make replacement heat exchangers and they think 15psi back pressure is normal @3000rpm. Upon closer look at this VP overheating troubleshooting guide, I realized that the pressure numbers they quote are for raw water cooled engines. Hence, my previous conclusion about potential blockage downstream (based on high pressure readings) is off. So, it appears that heat exchanger is not the problem after all.

2. So, I went back to focusing on the pump and the upstream part of the raw water system. Took the pump (new pump) apart, inspected closely the impeller and the insides - nothing suggesting any damage or defects. Back flushed the intake system (thank you Scott for instructions). I flushed separately the hose that goes from the oil cooler to the pump and the entire intake system. Looks like I am getting solid flow on the other end - no signs of debris coming out. That, combined with normal vacuum readings, convince me that the intake system is fine.

What do I do next!?

 

[Lou C]

well if those manifolds are only a year old they must have gotten hot enough to burn the paint off because there is hardly any paint on them!
The one thing that caught my eye was the raw water connection on the front end of the manifold, is that right angle fitting too restrictive? Is that OE or was that done during the closed cooling install? I might want to get a longer 3/4" hose and use a straight hose barb fitting into the manifold to straighten the flow. Nothing else jumps out at me though. Some Volvos and OMC's use a 90* elbow there, but not sure if that's what yours has. I have the 90* ones on mine...the exhaust runs pretty cool, max after off plane is 130 or so.

 

[ripjmk]

I see you removed the top end cover from the heat exchanger but have removed the one on the bottom? if there is any sediment thats where it will collect.

 

[saf]

Thanks for the comments. Here are clarifications on the issues you are picking up upon:

The starboard side manifold was burnt, indeed. Happened last year right after the install of new risers and manifolds. Starboard side riser turned out to be defective leading to flow blockage and overheat (and cascade of failures). The port side manifold did not burn. However, I do have a moisture problem in the engine compartment. There is always a small amount of water at the bottom of the bilge (below the engine), the bilge pump cannot get it all out. This water evaporates during the day and condenses on engine parts at night. All the metal parts are constantly covered with moisture, hence, rust everywhere. I am getting the "dry bilge" system installed to fix this...
You are also correct about the port side manifold water connection. This is a plastic 3/4" 90 elbow put in by the mechanic who did the manifold install for me (now I wish I did it myself). The original preformed hose was bad and he could not find a VP replacement, hence, the plastic elbow. The worst part of it is that he changed the fitting on the manifold to 3/4" (instead of the original 1"). The starboard side manifold, however, still has correct fitting and the original VP preformed hose. Since both sides run at the same temperature, I assume the inferior water connection at the port side is not an issue, at least with current water flow (it might become an issue once I fix the water flow problem, but this is my next battle).
The heat exchanger pic was merely meant to show its type, i.e. it is a 3-pass exchanger (I believe). I did open the other side of it (multiple times now) and could not find any issues.

 

[Lou C]

In this pic when I installed the new exhaust 3 years ago you can see the 90* fitting used by both OMC and Volvo. They are for 3/4" hoses and might be less restrictive.....

 

[saf]

Another update (the struggle continues):
I did the ultimate (I hope) raw water pump test. With two 90 degree 1-1/4" elbows and about 6' of reinforced 1-1/4"ID hose I built an intake system for the pump: straight run from the pump to the transom (under the engine), 90 elbow, straight run to the deck, another 90, gently curving (within the allowed curve radius) run to the water level (the boat is in the slip). This should be much less restrictive than the built-in intake going through the outdrive. The output 1"ID hose goes straight from the pump to a bucket. With the engine being cooled from a fresh water hose, I ran this setup through the entire rpm range and measured the flow rate. This is what I am getting: 7G/min@1000rpm, 20G/min@3000rpm, 24G/min@4000rpm
This resembles closely the numbers for Johnson F5B-9 crank-mounted pump used for GM 350 engines (see attached chart)

So, I am thinking the pump is fine (as designed) and the 24G/min@3000rpm in-situ figure is for 454 block pumps (see the chart)

Now, the moment I put ANY restriction on the intake (or outflow) the flow rate drops, especially at high rpm (not surprising). For instance, if I connect my test intake system to the outdrive (through 1-1/4"x1" coupler) I cannot get the flow rate above 20G/min. The vacuum readings at the pump are consistent with VP specs for DP-SM outdrive, i.e. <10inHg (~5psi). This, combined with the fact that the water intake system in the outdrive was rebuilt last year, tells me that this is normal.

Here is another bit of information: I spoke with a VP dealer, they, in turn, contacted the regional VP rep; the word is that the operating temperature for exhaust manifolds in my system is 160--200F !!! and this is NorthEast, i.e. ocean water is generally <70F.

So... it is starting to look like there is no problem!? Risers in my system are expected to get this hot!? Is there anyone on this forum with a similar system, i.e. 5.7 carbureted V8 with fresh water cooling and pre-1999 (pulley-driven) RWP? What is your experience?

I am going to try to upgrade to a crank-driven pump for 454 block, we'll see what happens...

 

[saf]

The season is almost over here in NE. So, I'd like to offer some closing notes to this issue. I did the raw water pump upgrade - upgraded to a crank-driven Jabsco high flow model. This nearly doubled the flow rate at low rpm. Riser temperatures also dropped. However... the flow rate still maxes out at 25G/min and the riser temps still climb above 200 @ WOT (according to the sensor, a bit more on that below). Seeing what 25G/min look like, i.e. water gashing out of 1-1/4ID pipe, I do believe that it is impossible to achieve much higher flow rate with an impeller-type pump through the restrictive DP-SM outdrive and 14" 3-way heat exchanger. At this point I do not believe the raw water flow rate is the issue. The issue (if it is an issue) is two-fold:
1. Risers in my setup (fresh water cooling with DP-SM outdrive) are designed to run hot. Even though this information is not published anywhere I did get a verbal confirmation from a VP representative that risers in my system run 160-200F
2. Temperature readout from sensors is slightly higher than the actual "average" temperature of risers. Infrared thermometer shows temperature varying from 150 to 200 in different spots of the riser. The sensor location happens to be the hottest spot.
So, not a particularly satisfying result. However, I want to call this issue closed, unless someone here sees something that I missed...