Good New, It's Fixed!!-RWP just Can't keep up!

S

stuartdmc

Member
Joined
May 1, 2006
RO Number
21081
Messages
97
Here we go again with another overheating issue.
My question is simple, Does the "RWP" (Raw Water Pump) provide a larger volume of water to the risers and heat exchanger cooling down the "FWC" (Fresh Water Coolant) at higher RPM's?

We'll my 1998, 454 7.4 VP doesn't keep the engine cool at high RPM's. I can run 5 to 8 MPH all day long but when I accelerate and run on plain for a minuet or so the temperature rises until the computer brings the engine done to the safe mode.

I have replaced the manifolds and risers, checked the flow and all seems clear the only thing left would be the RWP impeller? the circulation pump? or a blown head gasket? as for the BHG, there is no smoke, the oil looks good. so I have really ruled that out.

What else could be causing the engine NOT to be cooled down while under way at high RPMS?

Thanks all.
 
Worn pump around the impeller. See if there grooves on the surface that the impeller rides.
 
What's BHG? Too many abbreviations confuse the issue.

Sounds like a worn impeller AND housing.

What's the age of the raw water pump...as in when was it last serviced? How many engine hours since last time impeller was replaced.
 
Sorry,
BHG = Blown Head Gasket.
The plump is less than two years old. as for the impeller it may be older. I have a new impeller ordered well see what she does.
I noticed that the risers get extra hot to the touch when I run WOT as well as the heat exchanger which is only a year or two old.
quote:
Originally posted by jtybt15

What's BHG? Too many abbreviations confuse the issue.

Sounds like a worn impeller AND housing.

What's the age of the raw water pump...as in when was it last serviced? How many engine hours since last time impeller was replaced.

Click to expand...
 
You may have Impeller parts stuck in your Coolant passages.
 
Happy Camper- I don't believe that will help in this case.

Worn/grooved pump wear surfaces would mostly affect LOW rpm running , but generally not higher rpm when the impeller vanes no longer actually contact those surfaces.

Stuartdmc-
Yes, the RW pump should provide greater flow at higher rpm, particularly underway to include water-ram effect , but the engine of course puts out add'l heat then as well.

If there is a abnormal restriction in the RW side of the cooling system , there can be a finite limit to that increase flow below what is needed for controlled heat exchange and cooling.

Once the t-stat on the FW side can no longer compensate for the reduced heat exchange , engine temps go up.

Those new riser/elbows should be cool or perhaps barely warm to the touch if RW flow is sufficient.

How/where did you check RW pump output flow? The likely spec for that flow is 5 gal in 15 seconds at WOT, which is a lot. But I sure wouldn't be comfy attempting to check my engine's flow into a bucket at WOT. it's pretty hard to get a remotely accurate guess just by eye if T/H exhaust water flow is visible, though very low flow is evident.

Check RW intake for restricting excess paint or fouling, sea strainer basket and lid o-ring , RW pump impeller, transmission and crank oil coolers, slipping pump belt, suction hoses for crimping, suction collapse at high pump demand) or inside delamination, and then inspect heat exchanger bundles.
 
Stewart, did you have your outdrives serviced recently? I had a skeg repaired once where they had to removed the lower part of the outdrive. When they bolted the lower 1/2 back on, they didn't seat a water coolant tube properly that carries the raw water from the lower part of the lower unit to the upper part of the lower unit. When on plane, this tube was up and out of the water and would ventilate, which caused the engine to overheat. When I would come off plane, it would suck water again and temp would come back to normal. Frustrated the hell out of repairmen and took 3 weeks worth of troubleshooting to identify this cause. The fix was just removing the lower 1/2 again and reseating that tube properly and then reassembling the lower unit again.
 
Had the same issue and found that my raw water intake hoses delaminated on the inside. Water flow was pretty good but when you pushed the boat a bit, my heat rose quickly. It was amazing to see the partial blockage inside the hose yet the outside of the hose looked perfect. I changed the hoses and problem was immediately solved.
 
Look for ss not bhg. Your symptoms are usually lwf not bhg.
 
Most everyone starts at the wrong end of the cooling system (risers and elbows)when they start overheating. more likely you need to look at the oil cooler. quite often there is a blockage in the oil cooler restricting water flow through the rest of the system. if you ever opened up an oil cooler there are many very small diameter tubes that the sea water passes through. debris as well as old zinc block the water flow. I would start there. I have done this many times over the years and save a lot of time and money solving overheating issues
 
I agree, restriction on the intake side as well as a loose connection that pulls air instead of water, both will reduce water flow.

Something is causing reduced water flow. You'll probably have to pull each section of hose and component and back flush debris out. Also look thru the section of hoses if you can to find the delamination as mentioned.
 
I'm not familiar with Volvo outdrives but where is your raw water pickup? If it's thru the drives I would look there. The experience I have with Bravo drives is that is where the restriction is right where the raw water pickup hose goes thru the transom assembly.
 
Update,
I think you're on the right track, I replaced the impeller but what was alarming to me was when I pulled the intake hose off of the pump water ruched in as if the intake hose in the boat was below the water line. (my boat is in a slip 100% of the time) after replacing the impeller and went for a ride and it only over heats when I get on plane so enjoyed a nice harbor cruse. the next morning I pulled the boat out of the water and hooked the hose to the lower unit then I noticed water was flowing out of every small and large hole there was on the lower drive I went up and started the engine and noticed that it was getting hotter than normal quicker so I pulled of a RWH and it was dry as a bong no water at all was getting to the engine to cool it off.

Question,
In a Volvo Penta DP stern drive is there an impeller that turns with the shaft in the lower unit? or could something have come lose over time? that would not allow the water to be sucked in from the water hose? Note; I have not had any work done to the stern drive in a year or so. So if GoVols correct and I think hes on to it, can the lower 1/2 be taken off without removing the upper 1/2?
quote:
Originally posted by GoVols

Stewart, did you have your outdrives serviced recently? I had a skeg repaired once where they had to removed the lower part of the outdrive. When they bolted the lower 1/2 back on, they didn't seat a water coolant tube properly that carries the raw water from the lower part of the lower unit to the upper part of the lower unit. When on plane, this tube was up and out of the water and would ventilate, which caused the engine to overheat. When I would come off plane, it would suck water again and temp would come back to normal. Frustrated the hell out of repairmen and took 3 weeks worth of troubleshooting to identify this cause. The fix was just removing the lower 1/2 again and reseating that tube properly and then reassembling the lower unit again.

Click to expand...
 
Hey, STUART.
Sorry for the late reply. Yes, the VP outdrive brakes into 2 pieces. They pulled the lower 1/2 off in order to weld a new skeg onto my '04. Then, they bolted back on wrong, which started a month-long expensive investigation into the cause.

Now, since your boat stays in the water, you should check to see if you don't have a bunch of crap growing over your RW intake ports on either side of the lower unit.

I trim my houseboat's outboards all the way up before each outting in order to (1) clean off the fisherman's tangled lines in the props and (2) clean off the RW intake ports so the motors have a good unrestricted supply of water.

Good luck!
 
I've had a few Volvos and none have a pump in lower unit, only on front of engine.

But if you have water at the intake to the RWP, you should be good. Follow the flow. Is it a thermostat issue?
 
GOOD NEW!!
I had my out drive removed and the lower 1/2 taken off we found a nice "BIG" corroded hole in the copper goose neck intake tube that goes between the upper and lower half I replaced it and my boat "No Longer Over Heats!"
Now I can enjoy the end of the summer on the water.
 
Well, That IS the "Sucking air instead of water" issue. Glad you found it.
 
glad you found it and fixed it before it made you crazy! I've been there with a friends boat complete opposite problem boat would get hot at low rpms but fine at higher rpms.
 
You must log in or register to reply here.
Back
Top