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techspecial
06-04-2008, 04:18 PM
My Minx with a 260HP 350 overheats at low RPM's...I need to keep it above 1000 to keep the temperature down.I replaced my Alpha one lower unit pump and inspected the impeller on my circ pump.I have no idea how old the manifolds and risers are but they're Osco's so there not original. If I need to replace them I'd like to switch to GLM aluminum...Yes I love Stainless Marine with chrome risers but I just don't have the ching for the bling right now. Any corrosion issues with them? Could it be something other than them? Should I remove my thermostat to see if that helps? Any ideas? Thanks in advance!!!
Mike

hardcrab
06-04-2008, 05:40 PM
Should I remove my thermostat to see if that helps?
Mike

You can try and replace the t-stat, but removing it completly isn't the right idea. The t-stat is meant to retard the flow of coolant allowing it to absorb heat, removing it will allow the coolant to pass thru the system too quickly to effectivly take the heat with it.

MOP
06-04-2008, 06:40 PM
A lazy Tstat is possible, stuffed up manifolds will not cause low speed over heats. Being as you just had it apart my guess is the water tube seal is leaking! Do a simple test get a length of clear hose. put it in place between the tstat housing and the manifold. Run the engine and watch for a bubble trail in the water, that will tell you if the seal in the drive is leaking. This is a good test on any drive for air ingestion, many drive will suck air as the boat goes on plane lifting the main body of the drive out of the water. What can be happening is the heads fill with air from the bubbles and it over heats. On some as speed picks up the air gets pushed out, most of the time not. But the test is simple and conclusive.

Phil

Tony
06-04-2008, 07:30 PM
Three years ago I hauled my new to me 22' classic down to AOTH VI, without ever having dropped it into the water. Once there I also had low rpm overheat problems. After a cool down, it was fine as long as I stayed on plane.

To make a long story short, and after trying a new thermostat (thanks again, Trueser!), it turned out to be a hairline crack in the plastic fitting of the water inlet, on the inside of the transom. A little two-part epoxy repair and I was good to go.

:beer

RedDog
06-04-2008, 09:02 PM
... The t-stat is meant to retard the flow of coolant allowing it to absorb heat, removing it will allow the coolant to pass thru the system too quickly to effectivly take the heat with it.

is this what you call "new physics"?

cutwater
06-05-2008, 07:59 AM
is this what you call "new physics"?

That's what I was thinking...

MOP
06-05-2008, 08:35 AM
The water flow temp thing is real in some applications, when I was racing Ford 60's we tried removing the Tstats as we had some problems with them. We over heated in a lap or so, I was told if the water flowed to fast it did not remove as much heat. We ended up putting a washer in place of the Tstat with a 5/8" hole then the temps came back down so the statement is true, but like I said not on all applications.

ky-donzi
06-05-2008, 09:30 AM
I agree with MOP as far as flowing too fast in an automobile, BUT I believe that what the problem is that it flows two quickly thur the radiator to remove the heat. What happens when the t-stat is removed is the water picks up heat in the engine flows to the raditor (rapidly flows thur since there is no t-stat and heat is not disapated into the air)

Now on a boat, Im not sure since the lake or river ect. would be the raditor..... I would think that it would not matter how fast the water moves thur the engine...but I could be wrong...

Anyway a restrictor will probably solve the problem I have used them on cars were no t-stat would cause overheating.

cutwater
06-05-2008, 09:49 AM
The water flow temp thing is real in some applications, when I was racing Ford 60's we tried removing the Tstats as we had some problems with them. We over heated in a lap or so, I was told if the water flowed to fast it did not remove as much heat. We ended up putting a washer in place of the Tstat with a 5/8" hole then the temps came back down so the statement is true, but like I said not on all applications.

Running a car w/ no t-stat might make it overheat, but it would have to be due to some 2nd-order effects. The root of the problem isn't that the water is flowing too fast to heat up.

BigGrizzly
06-05-2008, 09:49 AM
Hardcab That only applies to old Fords and some Christler motors the fords had a internal bypass that had two problem 1 a rebuilder problem of removing what was called a restricter which is actually a diverter to move water to the heads. Predominately in Ford Cleveland's. In the 1960s and early 1970s they made up this tail, because of lack of research. Now if the hoses were big enough and water moved fast enough, it could produce a thermal barrier and cause this. In some boats removing the T-stat the gauge reads hot but the engine is actually cold. This was Russ Kilby's problem on his 16 with a 289 Ford. You could actually sit on his exhaust and it was cold. I am not trying to get into a discussion because I believed it too until It was proved to me.:smash:
This was a common theory at the races in that era.

ky-donzi
06-05-2008, 10:27 AM
Cutwater

I will agree and disagree (automobile related)

The problem (of heat build-up) is probably something else, higher compression, improper timing, lakc of air flow throw the raditor, ect.

But I have personally seen a t-stat removed cause the temp to rise because the water flows so fast thru the raditor that the heat exchanging effect was not able to take place as well as it should.

the water flows to fast to cool down in the raditor.

VetteLT193
06-05-2008, 12:22 PM
If taking the T-stat out doesn't work, and MOP's trick to check with the air in the line is proves that a leaky seal isn't the culprit I suspect the waterpump.

I've seen more than one pump fail slowly and work better with more RPM's. At slower RPM's it's probably just inhibiting the water flow. I pulled the pump out of one of my corvettes that was working just like this... slow speed heat issues. no leaks. I decided to change it because it was old, and to rule it out. When I pulled it I was shocked it was even holding together...

Cuda
06-05-2008, 12:35 PM
You can pull the t stat, drop it in a pot of hot water, and see if it opens. I never run a t stat, and I've had no problems with overheating on any of my boats.

As far as overheating in cars, back in the day, the first thing I would do, was pull the t stat, and throw it in the ditch across the street.

MOP
06-05-2008, 03:28 PM
I doubt that the Tstat is the problem, the Tstat opens against it the water flow the water does not push it open! As far as running without a Tstat not good, you can be down in power and the muck build up in the engine is amazing. A good performing clean running engine needs a Tstat, the only engines recommended to not run one is super charged marine apps. Big Green talked about the muck build up in his engine as have others, running no Tstat will only lead to grief most notably broken valve springs, and rusted push rods and some other internal components!

hardcrab
06-05-2008, 05:00 PM
is this what you call "new physics"?


no.. basic science

Cuda
06-05-2008, 05:25 PM
I doubt that the Tstat is the problem, the Tstat opens against it the water flow the water does not push it open! As far as running without a Tstat not good, you can be down in power and the muck build up in the engine is amazing. A good performing clean running engine needs a Tstat, the only engines recommended to not run one is super charged marine apps. Big Green talked about the muck build up in his engine as have others, running no Tstat will only lead to grief most notably broken valve springs, and rusted push rods and some other internal components!
You have to keep in mind, the water temp in the gulf can top 90 degrees. The 22 runs right at 140, which is exactly where it ran before I pulled the t stat.

Cuda
06-05-2008, 05:26 PM
I have to agree with Reddog. I don't see how warmer water, would remove more heat.

RedDog
06-05-2008, 05:26 PM
no.. basic science

yep - that's what I thought. Although it may be too basic and too non-scientific

Need to venture into thermodynamics and fluid dynamics

Now the explanation of flow being too fast through a car radiator to cool sufficiently makes sense. Fast flow though a block cooling less than slow flow - uh uh...

cutwater
06-05-2008, 05:32 PM
no.. basic science

... or not science at all. Pull out the ol' Thermo textbook and get a refresher.

In a radiator application, too much water flow makes sense because water is no longer the coolant when it's in the radiator, it is the water that is BEING COOLED.

hardcrab
06-05-2008, 06:53 PM
OK, I retract my opinion.

I also didn't suggest it was the root of the overheating problem either. I did suggest a t-stat installed was better than none.

:hangum:

joseph m. hahnl
06-06-2008, 09:27 AM
There is not enough information.
Cooler, Salt water boat

The thermostat thing is way out of control.

There are fundamentals to cooling and operating temp.
190F is standard operating temp.
Some people remove thermostat(Mickey Mouse and Goofy ).
:crossfing: because there is a problem somewhere else. They don't Know how to fix or it is to costly to fix it so they take it out.
The engine was designed to have one and non use decreases performance by not allowing the engine to reach it's optimal operating temperature

Plugged radiator Doesn't apply if you don't have a Cooler on it.

Hoses are Extremely important if they collapse or have pin holes in them.
If there is a leak any where The system cannot pressurize and it may overheat.
If it is collapses, restricted flow.Check that all hoses are sound

Clogged Sea strainer ,Damaged water tube and out drive impeller.
A piece of impeller clogging in an orifice in the engine.Was the impeller missing lobes?


This one Is a Mother: Shale(Iron Scaling) can form in the heads and water jackets Especially in salt water boats.The Shale is very thin but falls of in big sheets restricting flow.

Idle speed in drive. If the engine is idling to low in gear it may overheat.
Set idle factory spec.

Running to lean .If the idle mixture is to lean the engine can run to hot at idle.Set to factory spec.

MOP
06-06-2008, 10:24 AM
Very doubtful that anything is plugged up, if something was it would get hotter as speed increased not cool down. My feeling is only two things the hose between the drive and gimble is collapsing but being forced open at higher pressure or air being introduced into the system. On trailered boats the gimbles rubber parts bellows, shift bellow and the hose should be replaced every 2-3 years need it or not! On wet boats they last year or two longer being kept wet, they dry out on our boats.

Pismo
06-06-2008, 01:04 PM
You can try and replace the t-stat, but removing it completly isn't the right idea. The t-stat is meant to retard the flow of coolant allowing it to absorb heat, removing it will allow the coolant to pass thru the system too quickly to effectivly take the heat with it.


A thermostat exists to allow the engine to retain heat, restricting flow until the engine is warm. The faster coolant moves through an engine the more heat it will carry away. 150F is a nicer temp.

Cuda
06-06-2008, 06:23 PM
If it's a saltwater boat, keep in mind that salt tends to crystallize very quickly above 140 degrees.

techspecial
06-12-2008, 08:16 PM
After chasing all of the things that we're "low hanging fruit"...
Alpha One water pump...Circ pump inspection...New t'stat...
Hoses...Belts...Sweat in early 100 degree heat...
A five minute conversation with my local mechanic yielded
"Are your ball checks in the t'stat assembly seating firmly?"
Thankfully they were not...NEW SPRINGS!!!
Thanks for all the help guys!!! Especially the spirited discussion
about heat exchange and thermodynamics!!! Appreciate it!!!
Thanks, Mike

penbroke
06-21-2008, 08:43 PM
Thanks for posting the end result. So many threads are just left hanging. My "other boat" just started doing the exact same thing...


Frank

MOP
06-22-2008, 06:58 AM
There is a better thermostat housing with no ball checks, I have a spare if you need one. I did not use it on the new setup being F/W cooled, it had maybe 10 runs and flushed it is in decent shape.

Phil

BigGrizzly
06-22-2008, 10:25 AM
I should stay out of this but I can't. With all your guys infinite wisdom can take out a T-stat that has been running for years and almost every engine in the world uses one, and solve a problem. That kind of thinking is called a band aid and NEVER solves a real problem. Some of you guys ought to figure what a t-stat is really used for. It is NOT just to help engine to reach operating temperature faster. Of course when I was 16 I to was of that opinion-wrong! I worry when my engines runs too cold.

penbroke
06-22-2008, 08:47 PM
I always thought the purpose of the thermostat was maintain the engine at the proper operating temperature by controlling the flow of coolant.

Phil: I have not looked into the ball check thing yet but I might just take you up on that. I'm thinking that the ball check thing is there to insure the engine gets first dibs on any available water flow that it needs and the rest is dumped through the exhaust manifolds? ...and if they don't seat correctly the water doesn't go through the engine but out the exhaust?


Frank

MOP
06-22-2008, 09:23 PM
I always thought the purpose of the thermostat was maintain the engine at the proper operating temperature by controlling the flow of coolant.
Phil: I have not looked into the ball check thing yet but I might just take you up on that. I'm thinking that the ball check thing is there to insure the engine gets first dibs on any available water flow that it needs and the rest is dumped through the exhaust manifolds? ...and if they don't seat correctly the water doesn't go through the engine but out the exhaust?
Frank


Frank I have worked a few hundred ball check setups the were a poor design to say the least. The balls unseat to supply the manifolds and risers prior to the tstat opening but if the tension is off they dump to much water and over heat the engine. At the dealership we got so fed up with them we played with washers held in place by the hoses, a S/S washer with a 5/16" hole is far more reliable no springs to screw with. A Very A typical Merc design, Bar and a few others have put out a much better product.

penbroke
06-23-2008, 08:35 PM
It appears not all have the check ball setup? ...or maybe I don't quite understand... Actually I don't quite understand the ball thing. Keep in mind most of my time has been spend with the Ford/Volvo in the Donzi. This is what I have.


Frank

MOP
06-24-2008, 08:03 PM
You are right Frank that is the later style with the bypass and no ball checks, I am pretty sure you said you were running an Alpha. When was the last time it had a pump kit, I have seen them do the low speed heat thing just before they spit the blades.
Quote: Actually I don't quite understand the ball thing. Te ball checks would unseat and supply water to the manifold, problem was they were overlooked all to often and would either wear or lose spring tension. Once worn or lose sprung they would let to much water through to the manifolds and not enough to the block, you can eliminate the using a 1" S/S washer with a 5/16" hole. Hold the washer against the Tstat housing and shove the hose on to hold it in place. The balls were not the Balls! as my Boston buddy would say!!

Phil

penbroke
06-24-2008, 08:10 PM
It has 2 years on it. It was fine last year and we did a lot of idling in the locks...


Frank

MOP
06-24-2008, 08:23 PM
[QUOTE=penbroke;455023]It has 2 years on it.

Frank pull the intake hose of the hold it about 15 inches above the top of the transom shield start the engine, @ 550=600 you should have between 2" & 4"'s of head. You can also do the bucket test, run the engine at idle and put the intake hose in a 1 gallon bucket you should just about fill it in 60 seconds. Last but not least it is always a good idea to do the clear hoses from the Tstat housing to the manifolds, take it for a run and watch for tiny bubble trails in the hoses. That will show you if you have any air induction into the cooling water, the air will build up in the heads ans cause an over heat of varying degrees depending on how much is getting into the system. Any air is N/G and will only get worse.

Phil

penbroke
06-24-2008, 08:38 PM
Thanks Phil. Sounds like good advice. It will be a couple days before I will get down there.


Frank