Perkins 4-108 overheating

[Jubilee39]

The perkins on my Corbin 39 has always had a tendency to overheat from time to time. In the USA it was fine but in the Caribbean it would occasionally overheat. I finally solved this problem with an oversized heat exchanger as recommended by Sendur. It did not give me much problems in Asia and the Indian Ocean with the warmer water temperatures. In the past year in Greece I have not been able to solve the problem of overheat. I have taken out the thermostat, replaced the thermostat with new. Still overheats, cleaned the heat exchanger last year and it seemed to be okay. After winter layup with fresh water in sea water side overheated again first time underway. Raw water pump impeller looks okay, heat exchanger looks clean. A couple of Greek mechanics looked at it did the same checks I did and said they would come back the next day for a sea trial, never showed up . I then ran engine flush through the block, acid cleaned the heat exchanger and put a new fan belt on. Seemed to fix the problem, this was three weeks ago. I motored through the Corinth canal running full speed for an hour and half no problem. Next day started overheating again, I found the fan belt slightly stretched as I could just turn the water pump by hand. I tightened the fan belt again and still overheats but slower. Put a new fan belt on still the same, slowly overheats. The hull is reasonably clean, the propeller is clean, a 3 blade autostrean feathering prop which is slightly overpitched as full revs fall about 2600 rpm vs 3000. I have basically shotgunned as much as I can. What to do next? with a 30 year old engine could the water pump have lost efficiency? Should the raw water pump impeller be changed? new pump last year but the impeller was left in all winter. Should the thermostat be removed? Any suggestions appreciated.

[model 10]

Are you loosing water?

[jimbunyard]

Believe you may have answered your own question with this

"...prop which is slightly overpitched as full revs fall about 2600 rpm vs 3000..."

since you've tried all the obvious things and the problem is recurrent. Over-propping can definitely cause overheating.

[kenbo]

Originally Posted by jimbunyard

Believe you may have answered your own question with this

"...prop which is slightly overpitched as full revs fall about 2600 rpm vs 3000..."

since you've tried all the obvious things and the problem is recurrent. Over-propping can definitely cause overheating.

+1 on what Jim said

[skipperpete]

How is the overheat presenting itself? Is coolant boiling out of the header tank or is it just a gauge that gradually sneaks toward the red zone? Or is the overheat alarm going off?

[CSY Man]

. slightly overpitched as full revs fall about 2600 rpm vs 3000

Full rpm should be 4000, not 3000.
Sounds like you are way over propped..

[Jubilee39]

I have considered the pitch as being a problem but it has been the same for the last 15 years. The engine actually overheated when the mechanics were looking at it running out of gear at dock then suddenly came down indicating to me possibly thermostat was stuck. However there was evidence of plenty of circulation in the header tank. After doing the flushes on engine and heat exchanger everything seemed better. I have always had antifreeze in the engine but I am wondering if maybe this old engine with the aluminum header tank and exhaust my be deteriorating from the inside. Cleaning the heat exchanger several times in the last year seems to have improved but not fixed the situation. I am considering replacing the water pump but hesitate to do so as a guess because of the expense. I get a good delta T across the heat exchanger even when it overheated.boat speed is about 4 knots at 1500 rpm when it used to be around 5 knots

[Sojourner]

I have a perkins m80t, it is also over propped, max revs 2600-2800. Never gets a degree hotter than 82, its thermostat setting. Full throttle into wind might get it to 84. So I think OPs problem is elsewhere based on this and the intermittent nature of it...

[stormalong]

Have you checked your exhaust elbow for blockage? Restricted water flow into the elbow can cause overheat.

[jimbunyard]

Originally Posted by Jubilee39

...even when it overheated.boat speed is about 4 knots at 1500 rpm when it used to be around 5 knots

Unless you have a clutch, in the way that a vehicle manual transmission has a clutch, and it is slipping, overheating has nothing to do with boat speed; if the engine is turning at 1500, the prop is spinning at whatever the gear ratio in the transmission is changing the rpm to; the boat should move at the same speed given x rpm. If you're loosing a knot at 1500, that can only indicate a fouled bottom, prop and/or increased displacement.

Temperature fluctuations that you describe usually indicate trapped air in the freshwater side.

A freshwater pump can usually be rebuilt, if not, there are enough 4108s around that an aftermarket pump should be readily available at an economical cost.

Being overpropped doesn't necessarily mean that you will overheat, but it certainly makes it more likely.

The beauty of having a freshwater-cooled engine is that it limits problems with corrosion/erosion to the heat exchanger, and a well designed system shouldn't have problems even there.

Since you've retrofitted an aftermarket H/E, I would be tempted to review the plumbing routing of the raw water through the system to see if there might be room for efficiency improvements.

Oftentimes overheating problems are the result of several small factors working in concert; all must be modified a bit to get to the correct balance. A relatively low performance, low rpm engine like the 4108, in good mechanical shape, should not have any problems with overheating once proper operating parameters are recognized and fulfilled...

[Wotname]

Originally Posted by skipperpete

How is the overheat presenting itself? Is coolant boiling out of the header tank orlf? is it just a gauge that gradually sneaks toward the red zone? Or is the overheat alarm going off?

This is important as the answer will determine if the engine is really overheating or if you just have an indicator problem. I have had intermittent overheating and threw lots of dollars at the cooling system only to find later I had an intermittent gauge problem.

Originally Posted by stormalong

Have you checked your exhaust elbow for blockage? Restricted water flow into the elbow can cause overheat.

Again, important to determine if your raw water side is up to speed or otherwise.

Originally Posted by jimbunyard

........
Temperature fluctuations that you describe usually indicate trapped air in the freshwater side.

.......
Oftentimes overheating problems are the result of several small factors working in concert; all must be modified a bit to get to the correct balance. A relatively low performance, low rpm engine like the 4108, in good mechanical shape, should not have any problems with overheating once proper operating parameters are recognized and fulfilled...

Both good points IMHO.

[rbk]

When I had my head off last year on my 4108 I found old casting material in the coolant galleries. One shook out the other was too large to remove without risking cracking the head in the process. If all else fails check those galleries, you may have a slab of metal in there blocking the flow depending on how it feels that particular day.

[BigAl.NZ]

I also have a Perkins 4.108. At full throttle it is about 2900RPM. If I run her at full throttle the temp slowly but surely also creeps up until the alarm goes off.

I have done many of the steps you have, new impeller, raw intake, cleaned heat exchanger, change thermostat.

I have concluded, and it also says in some other threads, that this is not unusual for the 4.108 (we have the original HX).

If I don't push the motor beyond 2500RPM she runs all day happily at about 88 deg C.

I know this isn't a solution, but that's my experience with our motor.

[skipperpete]

One of the causes of a slow steady overheat on 4-108 perkins can be the flow of coolant NOT through and around the tubes in the core but at least partially straight down the outside of the bronze tube that wraps around that core. This was a big mysterious problem with Perkins Prima engines when the plastic ring that serves as a flow director was either left out or wrongly installed.
As a previous post mentioned , there is also the possibility of gas or air in the cooling system from a compression leak, usually seen as bubbles in the in the top tank and if a compression leak is suspected a cylinder leakage test is a relatively cheap and quick way to verify. Simply remove the injectors , hold the engine at TDC on the cylinder to be tested and force air above 50 psi into that cylinder via the injector hole and watch the top tank for bubbles.
As always , first make sure that the raw water flow through the exhaust is not impeded in any way by a corroded mixer elbow or collapsing exhaust hose.
I hope this helps ......Pete

[Jubilee39]

Thanks for the suggestions, I may have found the problem but not the solution. It overheated again and this time I found rust flakes on the inlet of the fresh water side. I had put engine flush through so maybe it disturbed corrosion. I will continue to watch and hope for the best