A27FC Overheating not cooling system related?

[Beta Don]

They made several hundred A27's powered with the 4D61 engine, most all of them I assume using the same clamshell scoop thru hull and the same 'home made looking' exhaust mixing elbow and since probably 95% of those boats are not experiencing overheating problems I would venture to guess that neither of those components are to blame for Ricks current problem

I installed a 100 HP Yanmar in my boat using that same clamshell thru hull and I could do about 11 or 12 knots in calm water at 3500 RPM and the engine never suffered any heating problems caused by 'turbulent or atomised' water. I would assume a 100 HP engine at 12 knots needs lots more cooling than a 4D61 at 2800 RPM doing 6 knots, so I wouldn't waste any time or $$$ changing out the raw water intake system hoping it *might* have a bearing on Rick's problem

Don

[tranmkp]

Good points but I suspect a good majority of those elbows are different - it also makes a difference in where the water is injected in the elbow.

Also consider that most if not all A27 owners don't really use their boats that hard - most have soft duty cycles.

Fact is you have a cooling issue at max rpm. You have checked everything that makes sense. It's time to think outside the box.

This would be a easy test if you have access to a 50 gal drum. Set the drum up to gravity flow to your detached intake hose. Run flat out and observe temp - that should put my theory to test. My boat had a y- valve that would allow me to flush out all the water channels and heat exchanger with fresh water. You could also put in a de-scaler and let it sit overnight then flush in the morning.

Did you check temp at elbow with IR gun. Remember water flow out of the exhaust is only a coarse indicator of water flow.

Just thought - have you removed the hose from the sea clock and opened it? Should flow like old faithful.

Good luck

[JT48348]

Brilliant idea!
But remember the molar mass of one gallon of water is 18.01528 g/mol. You will need to also compute the specific density of the material used for the 50 gallon barrel and compute for the left-handed transaxle shift of the planet. If it's Tuesday, don't forget to add the coefficient of 1.7gb/hrtz to your figures.

Since you're looking outside the box, have you considered that the water where you live may be slightly warmer than the factory specs when the A27 was built?

Or


You could have a problem in your coolant system....

[hetek]

You have a point there, JT. I seem to recall the comment I made about the Lehman engineers having cooling problems with the 4D61 was in the warmer climates. I also experienced higher than normal temps on my boat when we had a stretch of 100 degree days a few years back, but not enough to set off the hot horn.

Then again, tranmkp and CaptVic are both Texans where hot temps are the norm. CaptVic's boat, I believe, had an heat exchanger that may have been larger than the standard Lehman unit.

Question for tranmkp: I saw your video of your boat at flank speed. She was moving! But I also saw your comment that the temperature was 230 degrees. Did you ever solve that problem and if so, how?

rnummi's boat can only reach 2,700 rpm at 4.5 knots before getting into trouble. Seems like it should easily reach hull speed of 6 knots before overstressing the engine to the point of overheating.

Something IS up, but I think the effect of transaxle shift of the planet is negligible. Maybe we can skip that. Still thinking about the Tuesday effect though...

[JT48348]

Do not discount the transaxle shift.

[hetek]

Speaking of oil as a coolant...

You say your Dad bought Mobile One synthetic 30W50? I know synthetics are famous for their lubrication properties but I'm not sure about their cooling or heat exchanging properties. Maybe try to replace with old school dead dinosaurs: Straight SAE 30 for you boaters in climates above 60 degrees, per the manual.

Another thing not mentioned: Bleeding the air from the cooling system. "Most overheating problems are caused by the presence of air in the cooling system"...

Read pages 29, 30 and 31, here:

download/file.php?id=1489

It's everything Lehman had to say about the cooling system. Also, see the comment about using NPT 1" fittings, strainer, etc and appropriate size hose and full flow gate valves? "Reduced to 3/4" at the pump". Use wire reinforced suction hose "to prevent collapse under powerful suction of sea water pump."

Last, I had a 1985 Corvette once that would teter on the verge of overheating. Apparently, they are known for this. It was recommended by fellow Corvette enthusiasts that I use an additive called "Water Wetter" in the coolant . It's supposed to help the coolant transfer the heat from the engine more efficiently. I have to say, it did lower the temperatures some.

Hey, we're trying here!

[JT48348]

I had to stop painting my boat, I'm laughing so hard.

Please send me your $9.99, I will cast a spell using ancient Mayan runes. Then go back to checking your hoses etc. And don't forget a temperature gauge!

You guys kill me.
http://www.thetruthaboutcars.com/2008/0 ... AE-review/

[kerrye]

Last, I had a 1985 Corvette once that would teter on the verge of overheating. Apparently, they are known for this. It was recommended by fellow Corvette enthusiasts that I use an additive called "Water Wetter" in the coolant . It's supposed to help the coolant transfer the heat from the engine more efficiently. I have to say, it did lower the temperatures some.

Hey, we're trying here!

I used water wetter in an Olds 455 I used to drive with similar somewhat beneficial results.

[tranmkp]

The overheating was caused by a poorly designed exhaust elbow. If you can even call it that. It was just a header. Water was injected too far upstream. The heat would also start to burn the hose going to the muffler at the header transition. I replaced the hose with hi temp silicone, that part of problem solved. It would only get hot flat out. The heat would creep back and saturate the engine. A custom made SS mixer would run about a grand. i found a good deal on a four blade nibral prop and swapped out the flank speed prop- the effect was like swapping a 2.85 rear end with a 4.10! It was more fun to drive. At flank speed you could feel the boat flexing and oil canning all over.

The PO had that tall gear for low (quiet) rpm cruising - as the boat had done 2 great loops

Joe Puccia never intended for these boats to do the shenanigans that we do in them!

But what do I know?

[rnummi]

I had to take a quick trip to Phoenix so haven't been able to follow up. Man my boat has never left a rooster tale like that. You are absolutely right it looks like PT 109! All these suggestions will be addressed upon my return. I'll even wait till the planets are in perfect alignment.... I'm 90 percent sure it's gunk in clamshell. Heat exchanger was boiled...oil was changed, 50/50 remix antifreeze was used....

[dkirsop]

Salt build up or rust blockage in cooling passages? Have you flushed the engine with a salt remover such as Salt Away? A radiator shop can help with rust buildup in manifolds and exhaust components.

[rnummi]

Excellent suggestions. Is there a particular brand of Descaler everybody uses? Where do you get it? Pour it in leave it sit.what.....

[tranmkp]

http://www.saltawayproducts.com/

[rnummi]

Ok, the bottom cleaning partially worked.... had the diver poke holes with a coat hanger into intakes....said there was some minor buildup of microbarnacles... "nothing that would have effected anything" ... but definitely a little crust oness along side of seacock. I then changed / cleaned all the filters. Ran her up. Definite improvement. I now get 3250 rpm with about 160 degrees and about a solid 6.2 knots. Stays steady without temp fluctuations. Pushing to 3500-3700 rpm start getting closer to 180 degrees. 4000 rpm and she crosses 180 pretty rapidly. Definite improvement over pre-coat hanger but not yet fixed. Don had installed the groco north of the seacock with all new hose so it hasn't delaminated. Also now running without thermostat. I'm happy as a pig in mud at 3500 RPMs. Still can't get WOT without overheating though.

[Mainer]

Obviously I've come across this thread a few months after the inquiry, however, one thought that occurs to me is that your drive line may be impeded.

Specifically, if your engine/transmission is out of alignment and causing the propeller shaft to "bind" against the shaft log or cutless bearing, I would think that could be a cause of the symptom you described.

One way to diagnose is to disconnect the shaft from the transmission (with boat in the water) and measure the mating area at 4 different places to see how much one measurement differs from another. If more than 3 or 4 thousandths, you have an alignment issue that could cause the engine to work harder than it should at higher rpm's. Solution is usually to adjust engine mounts until mating measurements are good.

Also, rotating the shaft while disconnected from the transmission will give you a good sense of whether the shaft log or cutless are "binding" the shaft.