Cooling Configuration on 4-108 Perkins

[jimisbell]

I am having a problem with the temperature on my 4-108. It is NOT a major problem but its not right and I have been chassing the deamon for two months and think I may have found it.

The problem is that all is well when sitting at dock side at a fast idle. The temp goes up to thermostat temp and then stabalises there. BUT....leave the dock anp put a load on the engine and the temp begins to rise untill at 5 knots it is at 200F and it will go higher if I continue to add power.

I have replaced the raw water impeller though it was in good condition.
I have boiled out the heat exchanger tubes
I have checked the belt tension.
The flow out the exhaust pipe looks suffient.
I have checked the thermostat and it works at the right temperatures
I have checked the water temp guage against a laser thermometer
I have cleaned the raw water strainer..even though flow seemed suffient.

Now I am down to the freshwater pump...which is cast iron so shouldnt be a problem and a few odd things like the transmission cooler blocking flow but as I said the flow out the exhaust seems to be fine.

TODAY...I discovered an odd thing that might be the deamon I have been chasing! I would like confirmation that I am right before I make any changes.

In looking closely at the plumbing I noticed a hose that goes from a hose barb that is screwed into the head just aft of the thermostat housing. Best as I can tell this should be a bleeding plug, not a hose barb. The hose goes from here to a "T" in the return line from the heat exchanger between the heat exchanger and the port side input to the block.

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.

Does anyone recognise this hose or its purpose? Or have I indeed found my deamon?

[jimisbell]

Oh Yes, more data:

Raw ater temp at hull intake is 76F Raw water temp at output of tranny cooler is 77F raw water temp at output of heat exchanger where it empties into the exhaust elbow is 86F

Fresh water temp at imput to heat exchanger is 163F (thermostat temp) and at output of heat exchanger it is 125F.

I first found the "T" when I noticed that the temp along the return pipe from the heat exchanger to the port side block input varried considerably up and down along its length. Then I noticed the "T" with the hose going to the connection next to the thermostat.

A Laser thermometer is a really useful diagnostic tool!!

[Alan Wheeler]

There is so much info that is not here that this is a hard one to answer. Like, why has this been two months. Have you just purchased or did the fault just suddenly occur??
If the boat is new to you, it is possible that the hose may have once gone somwhere else. Like a Hot water heater or something. If that is the case, then bingo you found the problem. But if this is a sudden occurance, I am sceptical and need a lot more info for any of us to comment further.

[Boracay]

When I had my boat surveyed the surveyor used a heat sensitive "gun" to take temperature readings from different parts of the engine.
Such a device might assist if you can find one.

[svHyLyte]

I suspect what you are looking at is a line designed to feed hot water to the heating coils in a water heater, which is an arrangement we have on our boat. In our case we have a small valve that can be closed to block this flow which, at times, can be problematic as the hot water heater is under the berth in the port aft quater cabin and can really make the cabin unlivable during the summer months--but toasty during the winter!

Adding such a valve on that line--or a hot water heater--might be your solution.

Cheers,

s/v HyLyte

[jimisbell]

Originally Posted by Alan Wheeler

There is so much info that is not here that this is a hard one to answer. Like, why has this been two months. Have you just purchased or did the fault just suddenly occur??
If the boat is new to you, it is possible that the hose may have once gone somwhere else. Like a Hot water heater or something. If that is the case, then bingo you found the problem. But if this is a sudden occurance, I am sceptical and need a lot more info for any of us to comment further.

Yes, I purchased the boat in May and have had this problem from the beginning. But as I stated, its not a big problem unless I want to push it to full hull speed. But being a perfectionist I know its NOT right and want to fix it. My last boat had a 6-354 in it and it always ran at thermostat temp so I know this one can as well.

It would seem that even if this hose was for a water heater, it would be a problem. Once the water in the heater tank reached engine temperature then the heater would be operating as a "bypass" and be bypassing a lot of water around the heat exchanger.

I would think that an arrangement where the water heater was in series with the heat exchanger would be much more reasonable.

[jimisbell]

Originally Posted by Chris31415

When I had my boat surveyed the surveyor used a heat sensitive "gun" to take temperature readings from different parts of the engine.
Such a device might assist if you can find one.

That is what I used to get the temperature readings I reported.

[DeepFrz]

jimisbel; check your exhaust elbow.

[jimisbell]

Originally Posted by DeepFrz

jimisbel; check your exhaust elbow.

What am I looking for?????

I seem to be getting a good flow of raw water out the exhaust AND the temp rise on the raw water from in to out is only 10 degrees F so it looks like it is doing the job.

[jimisbell]

Originally Posted by Alan Wheeler

There is so much info that is not here that this is a hard one to answer. Like, why has this been two months. Have you just purchased or did the fault just suddenly occur??
If the boat is new to you, it is possible that the hose may have once gone somwhere else. Like a Hot water heater or something. If that is the case, then bingo you found the problem. But if this is a sudden occurance, I am sceptical and need a lot more info for any of us to comment further.

I answered the length of problem question, what other info can I supply other than what is posted in the above two posts??

[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?

[CSY Man]

I have had cooling problems on my 4-108 for almost 8 years now:

Any continous running above 2500 RPM will cause the temp needle to slowly but surely climb into the red.
(10 to 15 minuttes perhaps)

I can still run a 3000 RPM for a little while just to out run a squall, or even emergency power at 4000RPM if bridge is closing on top of me, for all normal purposes I am limited to about 2500 however.

Have tried everything to fix the problem...We did run a thread on this board about it a year or so ago.
Do a search on 4-108.

In the meantime, I have just about given up on the over- heat problem. Learned to live with it, like a spouse that snores and passes gas..Nothing is going to change..

As for the mystery hose, give me more info on the engine and I can look it up in the shop manual:

(It covers 3 kinds of 4-108s, low-line, old version, new version, etc. Which model is yours? Year?)

[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

[Alan Wheeler]

Thanks Jim, that helps me dramaticaly. Even with a water heater getting up to temp, chances are there is JUST enough cooling to keep the engine under control. Remember that the supply line to and from the water cylinder would be disapating as well as the water sink inside the tank. Plus and the very BIG plus, is that there would have been a flow restriction within that line. So water would not have been cycling around as quickly as it is right now. So adding all those together would have meant that the engine temp would have ranged within limits.
Right now with interupting that flow, your engine temp is actually a little on the low side. Not of concern, but certainly lower than it could be. 180 would be a good temp. So the original setup with a heater may have maintaned a closer to correct engine temp.

[jimisbell]

Originally Posted by CSY Man

I have had cooling problems on my 4-108 for almost 8 years now:

Any continous running above 2500 RPM will cause the temp needle to slowly but surely climb into the red.
(10 to 15 minuttes perhaps)

I can still run a 3000 RPM for a little while just to out run a squall, or even emergency power at 4000RPM if bridge is closing on top of me, for all normal purposes I am limited to about 2500 however.

Have tried everything to fix the problem...We did run a thread on this board about it a year or so ago.
Do a search on 4-108.

In the meantime, I have just about given up on the over- heat problem. Learned to live with it, like a spouse that snores and passes gas..Nothing is going to change..

As for the mystery hose, give me more info on the engine and I can look it up in the shop manual:

(It covers 3 kinds of 4-108s, low-line, old version, new version, etc. Which model is yours? Year?)

Mine is the "New" version. 1983 4-108M. It has the heat exchanger on the port side with the easily removable heat exchanger coils. AND.... the $250 molded rubber end pieces!!!

I could not see a "T" in the return water line from the HE to the block in any of the pictures in my manual so am begining to gain confidence that this hose is my problem.

If I were going to put a water heater in I would put it in series with that return line as the water temp there is 125F which is just about perfect for a water heater. This hose is in parallel with the HE and thus robs the HE of some of its fresh water flow.