Volvo Penta D1-30 Raw Water Flow Problems – Solved

The cooling system on G-whizz’s Volvo Penta D1-30 has never really seemed right, granted we could motor for hours without any overheating issues, however the water quantity exiting the exhaust seemed to be somewhat less than other boats with similar engines. For a few years the mechanic who performed the engine services said that we should keep an eye on the water situation, as he believed there was a building restriction in the sail drive, his suggestion was to split the drive and clean the water channels when the boat was out of the water. Now while the title of this post is “Volvo Penta D1-30 Raw Water Flow Problems – Solved” it was the problem that we had that was able to be solved not a panacea for all problems encountered, at the end of this post I have listed, to the best of my memory and with some thoughts in hindsight, the diagnostic processes I was going to use in the attempt to rectify this problem.

Eventually the exhaust water volume dropped to very low levels and there was a lot of steam at anything above idle speed. Something was amiss and it was time to do something about it.

Inspection of the system with the D1-30 running gave a couple of hints:
1. While there was water moving through the system there was apparently more air than water.
2. There was virtually no water in the strainer, just a trickle coming into the raw water strainer then down the outlet to the pump.

The first thing I did was to ensure the O-ring on the strainer lid was sealing by cleaning the ring and its mating surface then giving the ring a light greasing. This had no effect. Then thinking that maybe the water passage in the sail drive was restricted I followed some internet advice and boiled some water, closed the seacock on the sail drive, blocked the strainer outlet, filled the strainer with hot water then opening the seacock and quickly pressurising the hose with a dinghy foot pump, I did this a number of times, actually enough to empty the galley kettle then for good measure just pumped some air for a couple of minutes, the noise that came from under the boat indicated that there was no restriction in the inlet. What I did notice was that there was some water around the seacock on the sail drive, probably just a spill but the hose clamps were tightened just in case, put everything back to operational condition and started the engine – No better.

Returning to the strainer I again blocked the outlet closed the seacock and filled the strainer with water then went up onto deck to stretch and relax for a while, on return the water level in the strainer had reduced somewhat and there was indication of water around the top of the sail drive, so I removed the hose from the seacock to the strainer and gave it a good inspection for damage none of which could be detected, I gave the mating surfaces at both ends of the hose and the spigots on the strainer and seacock a good clean and a little smear of grease, replaced the hose. While the hose was off I also opened the seacock on the sail drive and there was a satisfying mini geyser of sea water coming in, enough to suggest that there was no restriction within the sail drive. With everything back to normal I started the engine.

Joy of joys the strainer quickly half filled with water, there were no bubbles in the hose on either side of the pump and there were copious quantities of water coming from the exhaust, the exhaust noise was also dramatically lower. There was obviously an air leak in one (or both) end the hose that was slowly getting worse, not a big leak but just enough to lower the vacuum generated by the pump, I’m wondering if the application of hot water and a bit of pressure opened up this leak sufficient for a small amount of water to escape and indicate that there was a problem, the reason I filled the strainer a second time escapes me but I am sure glad I did. While my memory of these things is not the best I reckon that there is more water coming from the exhaust than at any time since we’ve been looking after G-whizz. I also recall the previous owner telling us how important it was to prod the sail drive water entry from underneath at every opportunity to keep it free of restriction, maybe an indication that this air leak was there from new, maybe just a tiny foreign object in a hose to spigot join.

Volvo Penta D1-30 Raw Water Flow Problems – Solved. For a couple of days my mind was fairly active on working out a diagnostic process, what follows is sort of what came to mind in the period before tackling this issue. In hind sight the diagnosis of this problem was made easier by G-whizz having clear reinforced hoses in her raw water system enabling sighting of the water flow.

– Is air present in the lines? –
Logic would suggest that if there is air in the lines then there is a leak allowing air to get in this issue is going to be before the water pump where there is a vacuum in the lines allowing air into the system, if there it was after the pump where the lines are under pressure there would be no air but there would be a water leak. Check all the hoses and connections, remove, clean and/or replace, check the lid seal on the raw water strainer if fitted.
– Check the flow from the pump by redirecting the outlet hose to a bucket etc. –
If the flow is strong then the issue will be after the pump, to establish where it is repeat the flow test by removing the hose just before each component, anti-siphon valve, inter cooler, water to exhaust mixer etc. Keep in mind that you may be lucky enough for the blockage to be in the hose itself and not the component.
If the flow is not strong then the issue is going to be before the pump or the pump itself,  before diagnosing the pump itself check the lines for blockages by connecting an air pump (I used an inflatable dinghy foot pump) and pumping, if the the lines are clear there will not be much resistance to the pumping action and you will hear bubbling from beneath the boat as the air escapes from the intake. This action itself may “blow out” an obstruction. If there appears to be an obstruction try this just before any component in the line stating at the seacock and working back towards the pump  (Beware and take precautions as this is most probably below the water line) or you could just remove the hose off the seacock, open the valve and see what sort of geyser erupts, if it’s a gurgle not a gush the issue is in the skin fitting or the sail drive if fitted, if it’s the sail drive enter “clearing sail drive water intake” into your favourite search engine, a read all he scary and not so scary scenarios.
If no issues are found either side of the pump then it’s the pump itself. Remove the cover plate and check the impeller and the inside if the pump, Cover plate, back plate and inside surfaces for damage, it could be the seal on the impeller drive shaft or even the rubber section of the impeller no longer has purchase on the central boss, the pump is being driven but the impeller is not turning. Enter “Repair raw water pump” to get all the information and more that you could possibly want.
Another point that I got a bit obsessive about was how much water should there be in the raw water strainer with motor running. The answer to this was pretty obvious in the “brighter light of day” after I had rectified our system and that was; while the strainer will probably not be full, there should be a head of water sufficient that the inlet and the outlet of the strainer are well covered at all times.

The Volvo Penta D1-30 workshop manual can be found here.