Skin tank system

[Andy Drinkwater]

Request advice and comment on (my) skin tank system

 

Hello to all, and good to be on this forum!

We have a 57ft Ironworks narrowboat, build date documented as 1989, moored at Wenlock Basin Islington. As Ironworks do not exist anymore (as far as I know), I cannot consult them on my question, which concerns the design and operation of the skin tanks installed, as discussed below.

I have a horizontal skin tank either side of the engine bilge section, and these 2 form almost all the floor of the engine room, which is large. The coolant flow from the engine (heat exchanger) is routed vertically into one tank (via a hose connected to a +/- 30mm vertical stub welded at the front), and the other tank is similarly connected to the engine coolant pump for return. As the 2 tanks appear completely separated by the bilge section in-between them, I believe a +/- 30mm steel connection tube allows circulation from one tank to the other, and crosses between them at the aft end of the tanks. Estimating the surface area of each tank, and that they are +/- 2" deep (based on the depth of the engine bilge section), each tank may be up to 25 litres, which provides a cooling volume of 50 litres + engine volume + 30mm hose feeds; this seems very large to me.

 

I recently rebuilt my BMC 1800 engine after a long period without being able to run it. I reconnected the coolant hoses exactly as I had taken them off. When I test ran the engine, the skin tank on the RHS became warm (this is connected to the feed out from the heat exchanger) but the LHS stayed cold. I don't know if the connection pipe between the tanks warmed up or not, I should have checked. I am not sure if the tanks were circulating or not, with such a large potential volume I assume  it can take a while, but no sign of warm water in the LHS anyway. However I also believe that if there is no circulation (maybe due to a plugged connecting pipe?), then neither skin tank will not get warm?

 

My queries are:

1. Would this be a typical skin tank design/layout, and typical of the volume I have estimated? Am I correct to assume a 2" skin tank depth? If only 1" depth, of course the volume is 1/2 of my estimation.

2. Would such tanks normally have internal baffles, and if so is there a correct flow direction for coolant in / out? Or is this not important?

3. Assuming correct direction of flow in my set up (from RHS to LHS), is there any way to check and maybe unblock the connection pipe other than cutting it open?

4. If the system is truly this large, is the engine coolant pump adequate to pull the coolant up a 30mm pipe (+/- 1m long) and circulate as required? Or is any additional pump recommended?

 

Appreciate any advice and comments on this!

 

Best Regards

 

Andy

 

 

 

 

 

 

 

[WotEver]

1/ not typical, no. Skin tanks are far more effective when manufactured to be vertical, usually mounted on the inside of the swim. Only you can measure the depth - 1” would be far more effective for a base plate tank as it would keep the water closer to the canal. 

 

2/ Yes, that would be normal. Direction of flow is irrelevant on a horizontal tank. 

 

3/ Blow through the pipe that enters one tank and see if the air exits the other one. 

 

4/ Yes, it’s only a flow around a closed system. It’s not like it’s having to be pumped anywhere. 

 

I suspect you have an airlock somewhere. 

[TheBiscuits]

12 minutes ago, Andy Drinkwater said:

When I test ran the engine, the skin tank on the RHS became warm (this is connected to the feed out from the heat exchanger) but the LHS stayed cold. I don't know if the connection pipe between the tanks warmed up or not, I should have checked. I am not sure if the tanks were circulating or not, with such a large potential volume I assume  it can take a while,

 

If you do have 50+ litres of coolant, it will indeed take a while to warm up.  Were you running your test run hard and for a long time or only idling for a short time?  If you were treating your engine very gently after the rebuild I would expect that volume to take at least a couple of hours to get hot.

 

I'd be tempted to get some big tubs and pump the entire cooling system empty into the tubs, flush it through with clean water then either replace the coolant if it's good or renew the lot with new antifreeze mixed into clean water.

 

 

2 minutes ago, WotEver said:

I suspect you have an airlock somewhere. 

Seconded.  Is your coolant level correct since you ran the engine?

 

 

[David Mack]

If you have a closed circuit skin tank system, then the thing you referred to as a heat exchanger is only a header tank, possibly incorporating a water cooled exhaust manifold. There will be no heat exchanger core inside. One water pump will circulate coolant from the engine to the skin tank and back to the engine.

 

[Chewbacka]

If you have 2 fair sized skin tanks with a pipe joining them together then if the engine is only idling I would not be surprised if the water leaving the first tank is fairly cool and so the second tank will feel cold.

[Andy Drinkwater]

To all who replied to my qeries, many thanks! Sorry, wrong terminology, the header tank/exh cooler is what I have (Polar), no heat exch core installed. Yes, running engine very gently for now as just rebuilt, so likely warm coolant only stays warm until exits into 2nd tank as suggested. Definitely plan a longer test run to check total extent heat transfer - and if result unclear I will rig up a spare elec water pump to try and push water through 2 tanks.

Cheers

Andy

[Andy Drinkwater]

As a further comment, after I had topped up coolant and started to run the engine, and initial air trapped came out, the level stayed constant, so I think no more air was in the system. The RHS tank did get pretty warm, within 2 sessions of 30 mins slow running (temp gauge was showing cool to normal temp), different to previous engine runs (prior to rebuild) and I noticed this as my feet got quite warm standing on that tank! That's when I checked the LHS tank, which seemed quite cold. At that time I hadn't figured out how totally isolated each tank construction was from the other, I had thought the tanks had extended further under boat towards front, and the flow connection (whatever it was) was somehow at the front too, not visible. Now having felt the RHS (only) getting warm, and not the LHS, I examined & remeasured floor area, and noted the configuration of engine bilge area and tanks either side, and realised the tube at the rear would provide an obvious flow connection between the 2 tanks rather than any strengthening device (there would seem to be no need for a strengthening tube anyway, as the aft swim & uxter plate assembly is very solid & robust there.). Also, it makes a lot more sense if the flow connection between tanks is at the other end of tanks from the input/output connections.

Maybe one reason I noticed the warmer than before skin tank was because I had replaced the thermostat, as the old one seemed to be non-operational, so not allowing much circulation from the head to the header tank, then to to the tank.

 

Its a journey of constant discovery! and the one constant that I am certain of, is that every narrowboat is differently constructed from the next....