overheating above 4000rpm

[dennis461]

Volvo Penta AQ131C (AQ125) (automobile engine).
20' Renken cuddy cabin 270 drive.

Well, I was having trouble getting over 3500 RPM at WOT and 25mph.
Engine would stall, restart OK, idle OK then run good for a little longer.

So, I bit the bullet, put on new distributer cap, new spark plug wires, opened and cleaned all the gunk out of the 1-barrel carb
and got the engine running great.

Today we made three passes on the upper Mullica River in NJ at 20 MPH, up on plane, no sputtering water temps steady around 160.

So I pushed it harder hit 29.7MPH over 4000 PRMs, then looked back and saw steam billowing out of the cowl.
Had the 1st mate slow her down to 10MPH while I dumped water on the radiator and engine block (what the heck, I didn't pay much for the boat anyway.)
The new spark plug wires did there job, engine kept running and water temperatures quickly dropped right back to normal.
My stern rubbers are all new this season and the water necks did not show any leakage when I pressure tested.
So I don't thinks it's the up-on-plane overheating issue.
The exhaust manifold is new and the raw water pump send lots of water through the exhaust outlet onto the driveway running on my homemade muffs.

So here is the quiz.
Should I put the new impeller in that I was saving as an emergency backup?(The rubber impeller in there "seems" about as pliable as the new one)
Should I open up the radiator and looks for seaweed.
or
Should I stay under 4000RPM's

Sad part, I may not be back on the water till next season :-(

UPDATE to REQUEST FOR RADIATOR TYPE
This is the radiator I have.
Trapezoid shape with filter on the port side (filter near distributer)
http://www.volvopentastore.com/mall/image/view/7/7/8738_1.png

 

[sqbtr]

Re: overheating above 4000rpm

post a picture of the radiator you are speaking of about

 

[dennis461]

Re: overheating above 4000rpm

sqbtr

I updated my post with a pic of the radiator.
Your question reminded me that the filter/screen does not fit correctly, it is twisted up like a corkscrew, perhaps from old age.

Wish I'd have remembered that while cruising, I'll bet it collapsed under the higher water flow :facepalm:

 

[sqbtr]

Re: overheating above 4000rpm

Could be, be sure to check the water neck at the top of the intermediate section, they have a tendency to corrode and suck air when up on plane. Remove the hose to check as the corrosion starts from the inside.

 

[wellcraft19]

Re: overheating above 4000rpm

I would also put my money on a vacuum leak when on plane (or that the hose connecting the drive to the transom shield collapses under vacuum, blocking flow). If you suspect the impeller, replace it (simple). Running good on muffs that seal well will never help identify a bad impeller.
But since you mention that your sea water strainer (screen) does not fit correctly, I would almost assume that you have some "crud" that have passed by it and gotten logged inside the heat exchanger channels. You might still have "adequate" water flow, but not enough "surface area" to benefit from the water that passes through the H/E. Nothing wrong with that strainer, one just have to be a bit careful when putting in back in position. It really does fit "perfectly" when properly positioned.

Another issue, although less likely is that the water pump (the circulation pump for the closed system) is so corroded so it does not pump the coolant/glycol enough when at higher RPM. Or a combination of the two.

I have the same H/E as you. If you have not done it, take it apart, clean it out, inspect/replace all the seals/gaskets. And change the coolant. If you leave it for too long, it will slowly corrode that H/E from the inside (aluminium). A few photos before and after...

 

[dennis461]

Re: overheating above 4000rpm

Thanks,
The hose on the leg is about two months old.
And the neck was in very good condition when I put the hose on.

I'm kicking myself for not looking into the heat exchanger when I had it off last month for the timing belt replacement (so anitfreeze is new.)

As for the screen it is REALLY twisted up, like it was in a microwave oven or something.
I doubt it keeps anything out of the H/E

 

[dennis461]

Re: overheating above 4000rpm

Well, I have re-checked everything downstream of the filter (pump, copper tube, rubber tube above engine,metal tube to transom, rubber hose on the 270.
New impeller in place.
Near as I can tell, there must be an airleak where the internal tube/o-ring passes through the bottom section and the mid section.
Oil is good though.
I'm debating a through hull pickup vs rebuilding the drive for next season.
I've also ordered a DC powered water pump which I may Jury rig for next season as an emergency backup with some check vales and Rube Goldberg piping

See attached photo.
This will not draw water up from the barrel.
.

 

[PiratePast40]

Re: overheating above 4000rpm

The only way to find out for sure about suction side leaks is to test. One way is to hook up a garden hose to the chrome line on the inside of the tramsom. Block off the inlet hole on the bottom of the outdrive, put the muffs on and plug up the hole and then check for leaks at the water neck gasket and the lower water pipe o-ring (between lower and intermediate section). From that point, you can determne if the leak is in the most common places or if you need to start looking farther upstream.

There are thousands of these drive in operation and there are some common spots for leaks. Fixing those leaks makes a lot more sense than inventing some cobbled up system.

 

[dennis461]

Re: overheating above 4000rpm

The only way to find out for sure about suction side leaks is to test. One way is to hook up a garden hose to the chrome line on the inside of the tramsom. Block off the inlet hole on the bottom of the outdrive, put the muffs on and plug up the hole and then check for leaks at the water neck gasket and the lower water pipe o-ring (between lower and intermediate section). From that point, you can determne if the leak is in the most common places or if you need to start looking farther upstream.

There are thousands of these drive in operation and there are some common spots for leaks. Fixing those leaks makes a lot more sense than inventing some cobbled up system.

I did a similar test.
Put a small diameter garden hose up in the leg bottom hole.
Duct taped the leg inlets on leading edge (duct tape round and round).
Pushed water up into filter housing real easy.
Not a drop came out of the leg.

As for fixing the leaks, that is Plan A.
However, without a Plan B, I'll be sitting on the beach

Here is another thing I noticed.
The suction must be pretty good, the rubber hose between the engine and the chrome line at the transom gets slightly collapsed when testing.
I doubt it closed completely during this driveway test.
I plan to replace with a harder hose (it is another of the previous owners short cuts.)

p.s. did you notice the snow in the picture

 

[sqbtr]

Re: overheating above 4000rpm

Looks like about the same ammount of snow we have left, what part of the country are you from?

 

[wellcraft19]

Re: overheating above 4000rpm

Bet money on air leak in the drive. With water level "that low" (but hard to get it higher w/o dunking the boat though), the lower end of the water pickup tube is still above the water line.
You could try to tilt the drive a bit, and get the bucket up (or rather the stern down) in between the drive and the transom shield (careful so you don't squeeze the exhaust bellow).

And looking back at your first post again. When on plane the water level is normally below that same lower end of water pickup tube. If reading it right, runs OK when puttering around, as soon as you were on plane, engine overheated. Correct?

 

[PiratePast40]

Re: overheating above 4000rpm

Here is another thing I noticed.
The suction must be pretty good, the rubber hose between the engine and the chrome line at the transom gets slightly collapsed when testing.
I doubt it closed completely during this driveway test.
I plan to replace with a harder hose (it is another of the previous owners short cuts.)

That's one of those things that you'll find with an older boat. You just don't know what someone has done in the past and everything has to be verified correct. It can be frustrating, but you must make sure every component is doing the job it was designed to do or you'll be tearing your hair out when the simplest things don't work right. "As found" isn't always correct!

 

[bruceb58]

Re: overheating above 4000rpm

You need to put a clear piece of hose between the drive and the raw water pump to see if air is getting into the cooling water causing the raw water pump to lose prime. You can then look at it when you go over 4000RPM. Also, the problem with using a bucket like you are doing is that there is no guarantee that the raw water pump can draw that water up to itself.

It was mentioned earlier where the #28 in the following picture gets corroded and develops an air leak:
http://www.dougrussell.com/partscat...,3501,3502,3503,3504,3505,3506,3467,3466,3507

 

[dennis461]

Re: overheating above 4000rpm

You need to put a clear piece of hose between the drive and the raw water pump to see if air is getting into the cooling water causing the raw water pump to lose prime. You can then look at it when you go over 4000RPM. .....

I gotta laugh, no offense.
When we finally got the boat up to 4000RPM, I was too excited to even look at the temperature gauge !
The first mate was reading off the MPH from the GPS, the second mate was texting someone, and the engine was boiling over behind me !'

That ride alone was worth the $700 we paid for the boat and trailer.

I'll post up more test results before we get too much cold weather.
Thanks everyone for the help.

3000 RPM
http://youtu.be/UsPPf4VH9nE

 

[dennis461]

Re: overheating above 4000rpm

Old thread but I found closure.
After checking all the simple things, I gave up and put on a battery powered electric booster pump and sight gauge to get through last season.

The only thing that puzzled me was the waterpump housing end plate and internal face groozes. While these measured only .020", it was enough to keep the pump from working 100%.

I picked up a used pump with almost no wear on it. Put it in the boat and eureka!
I can now easily draw water from a tub of water and no problem at all on the water this year.