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Old 02-11-2006, 11:39   #16
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Quote:
Originally Posted by SkiprJohn
Aloha Jim,
You seem to have done nearly everything I could think of. I think the Perkins is a great engine and I know you said that the out temp is only 10 deg different from the in temp at your heat exchanger and is a low temperature and you seem to get good flow through your exchanger.
Something is still restricting the flow of cooling water through your engine.
Can you check the engine without the thermostat in place to see what temps you get?
Maybe a piece of impeller vane from a previous bad impeller or a hose that collapses or has a restriction in it or an internal port that is blocked somewhere.
Can you do an engine flush?
Regards,
JohnL
I think we are talking about two different flows here. The 10 degree difference was in the Raw Water temp, it was an increase from 76F to 86F. The Fresh Water (coolant) temp has a 38 degree drop from 163F to 125F
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Old 02-11-2006, 11:43   #17
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Quote:
Originally Posted by hellosailor
Jim, I confess I don't have a clear mental picture of your setup or hands-on with the 4-108.

"Then I noticed the "T" with the hose going to the connection next to the thermostat. " That makes me wonder. I knew an engine once with a similar problem, it worked fine at the dock but overheated under power. That one turned out to be a simple thermostat failure--but none of us realize the tstat in that engine was supposed to work as a diverter valve (a flow restrictor) in a t fitting.
That engine was raw water cooled, and the design of the t and tstat was so that all raw water was dumped out the exhaust, but as the tstat opened up it was diverted through the engine to cool it instead.

Which brings me to wonder, is the t fitting you are looking at definitely something someone added for a hot water supply? Or perhaps the engine was originally aw water cooled, and there's something odd about the way the freshwater cooling was added in?

Any chance it is something that simple, i.e. that someone kludged some part of the cooling system? Do you have any reference to check how much of what you have is "stock" and correct? If there's no reference to the t'd line you found...WTF, try closing it off and see if things go back to normal. Maybe it is "short circuiting" the coolant flow pattern.

And for sure, the tstat is not in backwards?
The thermostat has been checked(old one was fine), changed with a new one, and cannot be put in backwards. So that is all operating fine.

I havent any input as to whether the measurements I took were normal or not.
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Old 02-11-2006, 14:16   #18
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Aloha Jim,

I didn't misunderstand your post and my suggestions remain the same.

"As best as I can figure this 3/4" hose bypasses the thermostat and the heat exchanger...probably more water flows this way than thru the thermostat!!! I have no idea what this hose could be for and I dont see it in any of the drawings in the Perkins engine manual."

Jim, my engine is a Mercedes about the same size as your 4-108 and has the same thing and because I totally had to come up with a cooling system on my own I asked the same question of the person who sells me parts in UK.

As it was explained to me by my engine guru, "Whilst the engine is cold the thermostat is closed and routes the coolant back to the engine block via (in your case the hose barb) before the thermostat. Once the engine is warm the thermostat opens and directs the coolant flow to the heat exchanger.

That's probably why you are getting different temp readings along that route and the t would go to a heater if you want it to.

My last boat had a 4-107 and I loved the engine. It only showed signs of overheating when I was at 3000 rpm and higher for a prolonged period so my solution was to never run it more than 2500 except in an emergency. Worked fine for me. Usually I kept it at 2000 or below.

Hope this helps.

Kind Regards,

JohnL
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Old 02-11-2006, 14:48   #19
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OK, that sounds reasonable if the engine is designed that way. But on the Perkins the hose never shuts off when the thermostat opens thus it is ALWAYS bypassing.

I think the suggestions that it was for a water heater are making sense...even though that is not the best place for a water heater. I am going to clamp it closed for the duration of a weekend cruise this weekend and see how that works.

If I ever put in a water heater it will be in series with the heat exchanger, not in parallel to it.

Thanks for all the help and suggestions. I will be back Monday with a report!!
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Old 02-11-2006, 17:51   #20
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It is placed in that configaration for the reason of water flow and the amount of heat that should be produced from that area of the engine. It's no different to the heater in a car. The hot water is taken from an area of the block that produces a good excess of heat. Even though you may be getting a higher reading at the other end, you have to remember you are "cycling" the hot water. You do not want it to be related to the engine cooling system if at all possible.
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Old 02-11-2006, 19:55   #21
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Quote:
Originally Posted by Alan Wheeler
It is placed in that configaration for the reason of water flow and the amount of heat that should be produced from that area of the engine. It's no different to the heater in a car. The hot water is taken from an area of the block that produces a good excess of heat. Even though you may be getting a higher reading at the other end, you have to remember you are "cycling" the hot water. You do not want it to be related to the engine cooling system if at all possible.
But do yopu really want to by pass the cooling system with hot water. If you have it in the return line the already cooled water...which will be still hot enough to heat your water...is then used and the thermostat controlls the engine temperature. What you want is for the thermostat to controll engine temp and if you by pass the thermostat with some of your water you are defeating that controll system.
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Old 02-11-2006, 20:31   #22
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Hi again Jim,
If you do close that means of cooling the engine and go for a cruise your temp will rise extremely quickly and there will be a very dramatic increase in pressure at the thermostat because your engines water pump will be trying to force the termostat open. So please watch your temp gauge very closely and listen for hoses that might blow. If your hose blow and water does not get to your temp gauge it may not register that you've reached the boiling point. Have someone stay below and watch the steam rise.

Have you considered that your prop might be the wrong size and that it would be the cause of engine overheat if it is too large or has too high a pitch?

Kind Regards,
JohnL
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Old 02-11-2006, 21:18   #23
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Quote:
Originally Posted by SkiprJohn
Hi again Jim,
If you do close that means of cooling the engine and go for a cruise your temp will rise extremely quickly and there will be a very dramatic increase in pressure at the thermostat because your engines water pump will be trying to force the termostat open. So please watch your temp gauge very closely and listen for hoses that might blow. If your hose blow and water does not get to your temp gauge it may not register that you've reached the boiling point. Have someone stay below and watch the steam rise.

Have you considered that your prop might be the wrong size and that it would be the cause of engine overheat if it is too large or has too high a pitch?

Kind Regards,
JohnL
Thanks for the cautions.

All thermostats, of this type, are provided with a small hole that acts as a bypass so that there is circulation around the thermostat and the fresh water pump is not capable of building much pressure because of its design. Pumps of this sort have so much leakage that they just spin without moving water if there is any back pressure on them. They are designed that way. If there were any pressure, it would be between the pump and the thermostat...all cast iron block, no hoses.

The temp gage is at the thermostat so it will see the temp in real time as long as the "bypass hole" is functioning as it should.

The hose I am going to close is not a "means of cooling the engine" since it totaly bypasses the heat exchanger.

The propellor has been verified.
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Old 02-11-2006, 23:28   #24
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Jim you are totaly correct on the issue of the pump. It is a circulating pump only and has little pressure at all behind it. Certainly not possible to blow hoses with and as for the hose issue, you want no other means of water circulating anywhere other than through the "official" cooling system.
The hole in the stat by the way, is actually not for flow at all. It is to ensure that a temperature barrier is not created against the stat. With a little trickle of water flowing, it ensures the hot water does indeed reach the stat to open it. If it were blocked, the stat would have too much cold water for too long against it.
OK, now back to the main issue. Normaly that return to the engine would be in the engine block also. It would go nowhere near the heat exhanger. I imagine you will find another blanking plug in the block somewhere that would have once been connected. I imagine for ease of plumbing, the return has been plumbed into your exchanger lines for some gosh unknown reason.
simple fix is to remove the hose and hose tail in the head/block where ever it is and blank it off. Remove the "T" and put a straight joiner in. Better yet, put a new piece of hose right through so you have no chance of joint failures in the future. You should be set.
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Old 03-11-2006, 20:14   #25
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Right on the hole. When I said "circulation" that is what I was talking about. It provices circulation AROUND the thermostat so that the thermostat can work.

Thanks for the response. It validates my thinking on that "bypass" hose, as have several others posts. When I found that bypass hose it didnt look right and I really needed someone confirm that it had no other use before I took it out. The only thing I could think of was that maybe it was used in a cold climate and it might assist in initial warm up. But on the Texas coast I dont need that.

Tomorrow I am going on a weekend cruise and will take a pair of wood blocks and a "C" clamp to clamp it off for the weekend and confirm that it will help. When I get back with confirmation I will remove it all together.
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Old 03-11-2006, 23:10   #26
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Aloha Jim,
Have a great cruise. Would be interested to know how it turns out with the engine. I know my Mercedes is configured differently than your Perkins. Please be cautious.
Kind Regards,
JohnL
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Old 04-11-2006, 14:00   #27
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Had to cancel the cruise. I went down to the boat to start the engine and get ready to leave. It would NOT start. I have had this boat for 8 months and it has always started immediately whenever I tried it. BUT not today. After running the battery down I went to town and got some ether. One short shot and it started immediately!! The outside temp was 75F so that was NOT a factor. I have no idea what the problem was but by the time I got it started it was too late to join the cruise. The only thing I have done since three days ago when it last started perfectly was to clamp off that hose. There is no way in hell that clamping that hose would make it hard to start..#8-)

But I did run it at a high speed idle at the warf with that hose clamped and the temp went to 162F and locked in there. So its no worse than it was before clamping the hose off. Tomorrow afternoon I will take it out on the bay and see what happens....if I can start it.
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Old 05-11-2006, 22:24   #28
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After a two hour cruise today I find that the clamping of the "extra" hose has resulted in some improvement in the temperature. But it is not the whole solution. Tomorrow I will be pulling the fresh water pump to check the clearances and I will be checking out the transmission cooler.

On the 15th I am scheduled for a haul to do a bottom job so I will be able to look at the entire bottom to see if there is a flaw there. Maybe I am draging a bucket...#8-)

It seems that each thing I do results in a small improvement. Not any one thing seems to be responsible for the problem, but just a collection of faults, each minor in themselves, but culminating in a total that is unacceptable.

Thanks to all of you for your help and if you think of anything please post. I will report anything I find on this thread, so stay tuned.
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Old 06-11-2006, 11:54   #29
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Your circulating pump doesn't have any wearing surfaces, so clearances will not be a problem. You do need to check the front bearing for wear. The belt pulley should not seem wobbly.
Check the Salt water pump impellor. Ensure all blades are in good condition. If any are craked, replace it. If a blade is missing, ensure you find the missing piece. If the impellor is brand new looking, that too could be a suspect. It maybe possible that the previouse owner has replaced it and a broken blade has been traped further down stream.
I imagine this is the Engine fitted pump, so lets assume it is the right sizeing required. But if it is not the engine fitted one, have you got the right size pump?. If the pump is belt driven, ensure the belt is of correct tension and correct gearing to ensure proper speed. Ensure you have a large diameter intake hose. No "kinked" bends in it. No hose fittings other than the through hull and valve and ensure they are large enough. Impellor pumps do not like pulling water. They must have no restriction. Ensure the hose from pump to exchanger is free from kinks. And most importantly, ensure you have a clear water intake. Especially if there is a screen or filter fitted. Ensure no weed growth is inside the intake.
OK, with cooling aside now, what about RPM. Does the engine rev to full or close to full RPM when in gear. To check this, rev the engine to max out of gear and take note of the RPM. Now place it in gear and rev to max again. You should be able to get within 200RPM of max. If you can't, then your boat maybe over proped and over working the engine which will cause it to over heat.
There's a start, report after the checks and we will take it to the next step.
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Old 06-11-2006, 14:00   #30
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Jim, Bill Trayfors had some comments on his 4-108, either on this forum or SSCA. Turns out he had to replace his heat exchanger with a larger one. He of course had checked everything in the cooling circuit before hand and had several diesel mechanics check his engine out before making the decision to change the exchanger.

You should be able to find the thread by searching on 4-108.

hth,

Deep
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