Perkins 4-108

[Mediator]

That exhaust elbow is something else! Wow.

While you have the heat exchanger out, I would still drop it in some Barnacle Buster to be safe. The raw water passages look clear, but you also need sufficient space between the tubes for the engine coolant to circulate. On my engine even a tiny amount of crud will clog those up and make the overheating worse.

[BigAl.NZ]

Originally Posted by Mediator

That exhaust elbow is something else! Wow

Really it looks that badly clogged? Water still gets through as plenty comes out the exhaust and there is only maybe a 20% restriction.

[skipperpete]

Originally Posted by BigAl.NZ

Really it looks that badly clogged? Water still gets through as plenty comes out the exhaust and there is only maybe a 20% restriction.

Hi BigAl.NZ
The perkins slow overheat that I previously mentioned is better explained by these 2 photos and a really quick way to test if this is causing the overheat is to remove the rubber end cap and roll a fat oring down the outer case of the core bundle in situ until it stops at the alloy flange shown in the pic. Put the end cap back on, fill re up and see if there is a change in observed temp from before

[skipperpete]

The marked area on the core is where the alloy flange sits and should be a neat fit around the core..... a fat oring might be a bit hard to fit looking at the housing pic, the Prima seal is a tapered plastic one.

[BigAl.NZ]

Originally Posted by skipperpete

I'm sure this has been raised before on other 4-108 overheating posts but I'll mention it again. The cylindrical core stacks used on many engines are enclosed in a bronze/ brass tube with a hole through it at each end to allow the flow of coolant through and over the tube bundle. Raw water goes through the small tubes longitudinally. If the coolant flow is able to just travel down the outside of the bronze tube the heat transfer is greatly diminished and you get a slow coolant temp increase and eventually an overheat. To direct the coolant flow there was a flange inside the heat exchanger housing to stop the coolant from taking the shortcut outside rather than through the more restrictive tube stack. Perkins used several different methods to direct this flow including simply aligning the hole to the tubes with the circulating pump inlet or , on the perkins Prima , the inclusion of a plastic sealing ring around the core outer tube that had to be pushed into a casting sealing face in the housing.
The trick is to get a good flow of coolant through and around the tubes, not straight past em.
Hope this might help if you're having the slow overheat.
Pete

Ok with the benefit of reading this post and your pics, I understand what the ring does and the point your making.

Is this sealing ring not a Perkins part?

Cheers

Al

[skipperpete]

As far as I know, only the "Prima" and Penta MD 22 have it as a parts item ....and these engines really display the overheat when the ring is badly installed clear of the flange

[BigAl.NZ]

Originally Posted by skipperpete

As far as I know, only the "Prima" and Penta MD 22 have it as a parts item ....and these engines really display the overheat when the ring is badly installed clear of the flange

We have cleaned the exhaust elbow with acid and sand blasting and it looks near new now and unrestricted. We also have brand new rubber end caps.

I have rung Bowman and had a few conversations with them. As you correctly pointed out the rubber ring is only needed on the Prima series. The Perkins 4.108 has a metal flange down the same end as the filling neck - it is this flange which stops the water taking a shortcut.

There is no o-ring on tubestack - its just metal tubestack on metal of flange and Bowman confirm this. Will put it all back together tomorrow for a test.

Cheers

Al

[skipperpete]

Originally Posted by BigAl.NZ

We have cleaned the exhaust elbow with acid and sand blasting and it looks near new now and unrestricted. We also have brand new rubber end caps.

I have rung Bowman and had a few conversations with them. As you correctly pointed out the rubber ring is only needed on the Prima series. The Perkins 4.108 has a metal flange down the same end as the filling neck - it is this flange which stops the water taking a shortcut.

There is no o-ring on tubestack - its just metal tubestack on metal of flange and Bowman confirm this. Will put it all back together tomorrow for a test.

Cheers

Al

Glad to hear you're making progress. What I was trying to describe was the situation that occurs when that metal flange gets eroded/corroded and the gap gets bigger. A new bowman housing is quite a tight fit on the core but some of the old housings that I've kept have a 3mm gap all the way around the core and it was only after I solved the overheat on the Prima which has a 4mm gap sealed by a plastic sleeve that I realised that was the problem on the 4-108 heat exchanger... at least sometimes.
Hope all your hard work is rewarded by a cooler engine on the seatrial.

[BigAl.NZ]

Got it all back together today and ran it at high RPM, but out of gear for about an hour. Stayed at 88 deg C - not a true test since I never put any load on the engine - that will need to wait for another day.

I also measured the exhaust water flow rate - I calculated 16 Liters / minute - anyone know whats normal?