Under-Propped ?

[edwardc]

... and I am wondering if the alt bracket is working as a heat sink and drawing (rediating) heat off the head causing a "chilled" spot which is already under stress. The sides of the bracket work as "veins" rediating heat from a concentrated area. ...

What an interesting idea.

Sounds like we need a fancy infra-red camera (preferably video ) to take pictures of an A4 head under various conditions. Kind of like the ones they use to evaluate a house's winter insulation. (but I guess you southern California guys wouldn't know about stuff like that! )

[hanleyclifford]

Forum research

I begin to see the logic in the idea, different coefficients of expansion for steel and cast iron...are we working at the frontier of Afourology?

[Ball Racing]

My head was cracked when I got it.
It was always RWC.
When I vee'd the crack with a dremel and cut off wheel, and spot drilled it to JB weld it,,,,,
It was not much more than over a 1/16" of a inch of metal left.

Possible this side of the head see the most erosion from water flow direction?
When I run mine even under hard load I can lay my hand on the head and leave it, so I don't think the bracket is making the condition much cooler.

I feel some people running without a thermostat and the constant cold water just rushing into the motor is as much a problem as anything.
One side of the head is a combustion chamber with thousand degrees in it, and thru a quarter inch of iron if your lucky you have water sometimes not even a 100 degrees.

That makes it hard for metal to stay stable...

[Marian Claire]

A few details. The crack I experienced was in the exterior layer of the head. The inner layer was not compromised. The fact that water immediately sprayed and there are no external clues, discoloration, peeled paint etc makes me think the head was getting a fairly uniform flow. On removal some of the ports were restricted but none totally blocked.
I have the head at a friends shop and hope to investigate the crack next week. Will check on the thickness of the metal.
I do not understand how not having a T-stat would cause this problem. I believe the original design for the A-4 did not use a T-stat. On my and all the A-4s I have seen the water/coolant enter the side of the block and works its way up, thru and out the head. On the RWC system and new FWC system I have used recently the water/coolant entering the block is warmer than the water the boat is sitting in due to the recirculating loop. I could see the block/head getting shocked if the engine was run for awhile and then the thru hull opened but that was not the case here. Dan S/V Marian Claire

[Dave Neptune]

Flow

Daniel, I could see the water flow being an issue as it should be a consistant flow. I have not used a t'stat for over 26 years now and the head has been down for that long as well. I also run in water that does not get below 50 degrees. I kinda doubt that the heat sink is a culprit but just a contributing factor. The bracket also distribute its "load and vibrations" directly through the bracket.
I am also wondering if the cracked heads are after market or stock Universal heads?

Dave Neptune

[Ball Racing]

Thermostats?

In the car world, just because you ran with no thermostat , did not mean you were always running as cool as the gauge said you were,
as the water was running out so fast it never got a chance to "pull" the heat out of the metal parts.
I have the moyer bypass kit , the gate valve and checkvalve.
Lots of people say they control their temp with the valve.
I wonder if your really "always" changing the temp of all the metal areas, or just adding a extra flow of incoming water that cools the temp probe????

I think maybe we need various gauges at various places, and maybe even temp gauges that check block (metal) temps, not water temps.
We are worried about the temp of the oil, and moving parts, for over or underheating, not just the water..

Just as a thermos jug can be hot or cold on the inside, and you don't know it on the outside.

[Marian Claire]

I am 99% sure that the head that cracked was the original cast in 1965.
I received my used late model head, that I plan to use as a spare, the other day and noticed that 5 of the cooling ports are blocked. The three near the T-stat housing and two more down the water jacket side of the engine. My early model head had all the ports open. ???
I was concerned about the water vs metal temp issue so tried to monitor it. My water temp sensor is at the outlet of the manifold. I used my low tech oven thermometer to get a reading on the head itself. The base of the thermometer was wedged between the head and the manifold where the #2 and #3 exhaust ports are. It usually reads about 20 F higher than the water temp. When I turn off the engine the water temp rises to the block temp which makes perfect sense to me.
I will say that when I close my recirculating loop valve the water temp drops quickly. The block temp drops also but at a slower pace.
I have a small magnetic thermometer that is designed for use on a wood stove. I use it to monitor flue temps for safety as I heat with wood. I will try and take it with me on my next trip down to the MC and move it around the head and record temps. Never a dull moment. Dan S/V Marian Claire

[hanleyclifford]

Further drift

A question seems to arise here: does a faster coolant flow rate result in more or less heat extraction/exchange at a given point? Let's hear from the engineers with knowledge of thermodynamics.

[Dave Neptune]

Flow II

Dan, your absolutely correct about the speed at which the water moves through the system. On the A-4 with no T'stat you must use the bypass valve to restrict the volume going throught the engine to "maintain" an even temp. The only heating issues I have had in 26 years were when it was time to flush and once to replace the pump.
I had an interesting problem happen on one of my last cruises last season. As I was departing the marina I noticed the temp was a bit warmer than it had been so I popped the cover once in the outer harbor to take a look and give the bypass another nudge to closed and it did not respond as it usually would~~Hmmm~ somethings wrong. After pondering and looking around I decided that my water flow was far less than normal not good. So I pulled the intake off the strainer and the water just dribbled instead of gushing out found it, the problem that is. By now I am about 3~4 miles out of the harbor and only able to achieve 3.5 kts and I want to get to the island for an afternoon hike. I removed the hose at the thruhull and tried to poke through the valve and t-hull to no avail. It is mounted with a 90 where it comes through the hull due to space restrictions of the slole. Damn, need to go over the side with no one aboard and really did not want to do that. So I had a beer while "Ray" was still driving. As I sat and pondered I wished I had a diver or an air hose~ah hah~ an air hose would work but none on the boat. Then I spied a fire extinguisher and an idea formed!!! I stuck the hose back on the thru hull and stuck the extinguisher in the hose and duct taped it as well as I could. After hitting the handle and a big ga-dush. The hose and fittings were clear but not the cabin as the extinguisher did bolw off the tape and dusted the engine and myself and water was gushing out of the hose. And now there were some pretty confused crustations in the middle of the channel .
Dan On any H/P application I always modify the t'stat with a bleed hole as the engines are apart and back together often so one needs to insure that the system fills properly before making power. Don't neglect intake water temp changes if you run with no t'stat as it does make a difference. If your diverter is in proper orientation and operating order the heat distribution should be fine but it does take it a bit longer for the heat to settle as opposed to the t'stat. The main reason I run without is to keep the cabin cooler when motoring, the beastie is under my dinett and we often motor for 5 hours to get to the mooring before the wind starts and while the admirals ~ wife daughter and the Giz ~ are getting there beauty sleep.

Dave Neptune

[edwardc]

A question seems to arise here: does a faster coolant flow rate result in more or less heat extraction/exchange at a given point? Let's hear from the engineers with knowledge of thermodynamics.

A faster coolant flow definitely results in more heat extraction. It also results in lower coolant temps.

The rate of heat transfer between two substances is directly driven by the temperature differance between them. The faster flowing coolant doesn't get a chance to heat up as much, and keeps the temperature differance larger, driving a greater heat transfer rate.

[hanleyclifford]

A faster coolant flow definitely results in more heat extraction. It also results in lower coolant temps.

The rate of heat transfer between two substances is directly driven by the temperature differance between them. The faster flowing coolant doesn't get a chance to heat up as much, and keeps the temperature differance larger, driving a greater heat transfer rate.

So does it therefore follow that a faster flow rate thru the A4 will result in more uniform temperature throughout the block ?

[ndutton]

The rate of heat transfer between two substances is directly driven by the temperature difference between them.

And how long they're in contact with each other.

Coolant flow rate through the block is the same rate as through the heat exchanger. Inside the HX a slower coolant flow allows more heat to be extracted from the coolant - within limitations of course.

The point of use commercial water heaters (Insta-hot) are shipped with faucet restrictors to slow the flow through the heater to allow the water more time to pick up heat. It makes a dramatic difference.

A similar example is the old skool restrictors that were used in place of thermostats on Chevy small block engines.

[edwardc]

And how long they're in contact with each other.

Coolant flow rate through the block is the same rate as through the heat exchanger. Inside the HX a slower coolant flow allows more heat to be extracted from the coolant - within limitations of course.

The point of use commercial water heaters (Insta-hot) are shipped with faucet restrictors to slow the flow through the heater to allow the water more time to pick up heat. It makes a dramatic difference.

A similar example is the old skool restrictors that were used in place of thermostats on Chevy small block engines.

Don't confuse heat-transfer-rate with total-heat-transferred or temperature. Three different things. Temperature is a function of heat-transfer-rate and time (and a few other things, such as the specific heat of a medium and its volume). Heat-transfer-rate (eg - BTU/hr) is a function of the temperature differential between two points and the thermal-conductivity between them. Total-heat (eg - BTU) is a function of heat-transfer-rate and time.

In the case of the water heater, you're shooting for maximum water temperature, not maximum heat transfer. So slowing down the flow rate allows the water to get to a higher temp, but it simultaneously reduces the heat-transfer-rate.

Consider this thought experiment. In your water heater, if the water flow is reduced, the water temp gets hotter. If you reduce the water flow rate all the way to zero, the temperature of the water eventually rises all the way to the temp of the water heater's heating element. But now the differential temperature between the heating element and the water is zero, and the heat transfer rate is also zero.

Conversely, if the water flow rate is increased, the water temperature gets lower, and the temperature differential between the element and the water gets larger, and the heat-transfer-rate goes up.

Interestingly, the equations that govern all this look just like the ones that govern electricity. For example, Ohms law is

Voltage = Current x Resistance

whereas for heat, we have

Temperature-difference = heat-transfer-rate x thermal-resistance

In our A4's cooling system, the heat-transfer-rate at any point in time depends on the temperature difference between the block/head and the coolant at that point in time (as well as the thermal-conductivity, ie - how clean your cooling jacket is). Running coolant faster lowers it's temperature and increases the heat transfer rate. This higher heat-transfer-rate starts to lower the block/head's temperature, and thus starts to lower the heat-transfer rate, until everything settles back into equilibrium at a new, lower, temperature, with the cooling system still removing all the heat the engine is producing, but now at a lower temperature.

[hanleyclifford]

Ed, That last post is really good and important. Could you transfer it over to Bill's new thread on controlling temperature?

[Marian Claire]

Follow up to post 79. After grinding out the crack in the head the metal was 1/4 " thick. We may do a repair and then pressure test it.
Also I had a plate made that fits over the opening for the T-stat housing on the late model head I got. The plate is 1/8 SS so I should still have enough threads on the studs to fully engage the nuts. I will plug the temp sensor hole and pop out the "freeze plug" under the crossover tube and turn a late model into a early model head.
Anybody know why some of the cooling ports are blocked off in the late heads? I can understand the ones right under the housing but why 5?
Compare parts pic and the one I posted in post # 65. http://www.moyermarine.com/cgi-bin/s...rebuilder.html
Dan S/V Marian Claire