Seeing the thread on the 3" heat exchanger reminded me of an issue I've had. I won't go into the whole story, but it involved a sudden Chesapeake squall, halyard wrap/broken forestay and a tug pushing a barge running outside the channel.....
I was running the engine at full throttle and started to smell something hot. Looking at the temperature gauge, it's nearly pegged. I throttled back, went below and checked the engine compartment. No antifreeze, so the engine did not actually overheat/blow coolant, however, it did smell hot.
The boat was only a couple years old at the time, so I contacted Catalina who directed me to Westerbeke/Universal. Their reply was that the engine is not rated to run at full throttle. I sent an email, I believe to Bob McCullough who was tech editor at the time, and he said he didn't buy that arguement; I didn't either. As a test, I've run the engine flat out and within 5 minutes, the temp increases to near overheat territory every time.
I'm not in the habit of running full throttle, but in an emergency, need to be able to do so without worrying about overheating. It sounds like I might want to consider a larger heat exchanger.
Oh, and I've disassembled it several times over the years, passages are clear, no pieces of the zinc; I'm in more or less fresh water, so don't get salt byproducts. Change the impeller pretty much every year, have never lost a vane. Through hull/strainer clear, lots of water out the exhaust.
Any thoughts would be appreciated.
Gary and Cathy Price
1997 C36 Mk II Tall Rig/Wing Keel Imagine...
Hull # 1617
Worton Creek, Md.
Northern Chesapeake Bay
Gary,
Here is the site for the service bulletin for the 3" HX...
[url]http://www.realitycheck.me/docs/Universal_service_bulletin_195_heat_exch...
Chris
Chris Stewart
S/V "24~7"
1984 Catalina 36 Tall
Hull #251 M25
(SF Bay) Alameda, CA
Thanks for the link.
Should have noted, my engine is an M35A. The heat exchanger is 3". Symptoms sound the same though.
Gary and Cathy Price
1997 C36 Mk II Tall Rig/Wing Keel Imagine...
Hull # 1617
Worton Creek, Md.
Northern Chesapeake Bay
My personal experiences regarding running a diesel a full power for extended periods of time. This supports what Westerbeke told Gary about not running at full power for extended periods of time.
I have a Kubota L4300DT 4WD ag tractor, 43 HP, I never run it at full power even when drawing ground engaging equipment like a 3 furrow plow or a 14 foot cultivator. I've never run out of horsepower with it either, it will run out of traction way before it runs out of horsepower. The manual for my Kubota advises against full power operation for more than very brief periods of time, so I tend to believe Westerbeke on that point.
The M35A is based on the V1200 Kubota engine which came from the B2150 and B9200 tractors, these are smaller than my L series tractor and are not considered heavy duty industrial strength tractors (nor is mine).
I used to have a dairy farm in the '80s, we never ran the farm tractors at full power continuously. The dealer said if you're running wide open you're underpowered, they want 75-80% duty cycle maximum. A relative of mine walked in from the field one day leaving behind a 105 hp tractor with the bottom end blown out of it (broke the crank which came out the cast iron oil pan), he'd been plowing at full power.
I drove tractor trailers for a while after the farm went the way farms sometimes go. On long hills fully loaded the temp would climb up to just below boiling, then it was time to slow down, gear down and not blow it up.
We've only had any of our boat diesel engines at full power for about 45 secs, that was only for emergency maneuvering, once we got through that we powered down. We've been lucky we never have had to exceed that, if we had to I would but certainly you'd power down as soon as possible.
BTW, the transmission is also not designed to handle its rated capacity in pleasure craft on a continuous duty basis, they de-rate them significantly for that duty.
I've also always thought the heat exchangers were so tiny compared to the huge radiators in heavy duty vehicles, but water to water cooling is far more efficient than water to air. It just seems like cooling is so often a problem with small marine diesels you have to wonder if the heat exchangers are just not big enough.
Edit: Gary if it didn't lose any anti-freeze then you *likely* weren't really into an about to blow up type situation. The smell is telling you it's not happy, but the fact that the coolant didn't expand enough to overflow or burst any hoses kind of mitigates things in my mind.