Erosion and Corrosion

Thursday was just another day. Nothing out of the ordinary to report. I made my usual stop at Lucky Lou’s for happy hour with the crew and delivered a bag of fruit and vegetable scraps Donna saved for Mike and Jodi Hall’s tortoises. There was rain in the forecast due to hit us in the evening.

Back at home I didn’t fire up the Traeger – it wouldn’t be good to run it in the rain. So, Donna prepared chicken leg quarters in the convection oven. She cooked it as a one-pan meal with fingerling potatoes and kalamata olives.

Chicken leg quarters and potatoes roasted in the convection oven

Chicken leg quarters and potatoes roasted in the convection oven

They came out great, but next time, we’ll cook the chicken on the Traeger wood pellet fired grill to enhance the flavor of the rub and get the skin crispier.

Plate of chicken leg quarters and potatoes over XXX

Plate of chicken leg quarters and potatoes over arugula

The rain came later than expected. We had a lot of rain overnight, but it was dry and partly cloudy by morning.

Donna went kayaking with her friend Audrey on the Salt River Friday morning. She left just before 8am and I headed over to the Sports Complex for pickleball. After playing for two and half hours, I came home and relaxed. I finished the book I’d been reading and decided it was time to get after a few projects.

The first thing I attended to was testing the coolant on our Cummins ISL 8.9-liter diesel engine. In large diesel engines with wet liners, the coolant needs to have additives. These important additives dissipate over time. They aren’t needed in smaller diesel engines like the Cummins 6.7-liter ISB found in Dodge Ram pick-up trucks.

The smaller diesels aren’t built with wet liners. Their cylinders are cast into the block and machined to the final dimensions, making them an integral part of the engine block. On larger diesel engines, wet liners are common. This means the steel cylinder is a separate part that drops into the engine block. Seals on the bottom of the cylinder liner keep coolant from entering the crankcase and the top of the liner is sealed by the head gasket.

When combustion takes place in these cylinder liners, a vibration occurs – somewhat like ringing a bell. Although the amplitude of the liner vibration is very small, it’s enough to create a pressure wave that forces the coolant away from the outside wall of the liner. When the coolant moves away from the wall, it cavitates. The coolant then rushes back to fill the void from the cavitation and smashes into the outer liner wall. This happens on every firing cycle – so it happens several hundred times per minute while you’re driving down the road. Over time, this constant movement of the coolant can start to erode the steel cylinder liner. Think of it as wave action eroding a rock on the beach – but at a much accelerated pace.

Diesel engine coolant has additives to prevent cavitation and the sudden onrush of coolant against the liner. I ordered some test strips awhile back from Fleetguard. These strips are immersed in the coolant for 1 second. Then 45 seconds later, three pads on the strips change color and are compared to a chart. They show the freezing point of the coolant and the level of molybdate and nitrite. When I compared our strips to the chart, I saw that we were still in the safe zone, but should have more additive. I added a pint of Fleetguard DCA4 to the coolant.

Coolant test kit

Coolant test kit

My next project was to replace the anode rod in our Suburban 10-gallon water heater. When dissimilar metals are in contact with an electrolyte, galvanic corrosion occurs where one metal is attracted to the other. It’s the same electro-chemical principle that activates a battery. The water tank in our heater is metal. The water in it acts as the electrolyte – especially when certain minerals are present and other metals in the plumbing create the galvanic action. Most household water heaters have glass or ceramic lined tanks but galvanic corrosion can still happen as the liners don’t fully seal the metal components. It’s advisable to check if your hot water heater has an anode rod. You can get the basics here.

Our water heater tank has an anode rod that acts as a sacrificial metal. The rod will corrode in preference to the metal tank. As long as the rod corrodes, the tank will remain intact. However, the anode rod will erode away to the steel core as it performs its job, then it’s no longer effective.

The last time I changed our anode rod I used a magnesium based rod. These work really well but corrode more quickly than the aluminum alloy rods. I planned on changing it again after about 12 months. Well that was 18 months ago. Procrastination strikes again. I had a new aluminum rod on hand, so I got to work.

Our water heater is behind this panel on the living room slide out

Our water heater is behind this panel on the living room slide-out

First off, I opened the breaker on the water heater electrical circuit. Taking out the anode rod would allow the water heater tank to drain. You wouldn’t want the electrical water heater element to heat up without water in the tank – it would burn out the element in short order.

I taped a plastic bag below the anode rod to divert the water from the coach. Then I used a 1-1/16-inch socket on a half-inch drive ratchet to remove the anode rod.

Water heater and anode rod

Water heater and anode rod

Once I had the rod loosened enough, I realized I made a mistake. I didn’t turn off the fresh water supply and open the hot water tap to relieve pressure. The rod blew out of the tank with about 50 psi of water pressure behind it. I got a face-full of hot water filled with calcium carbonate sediment!

Oops - turn off the water and relieve the pressure first!

Oops – turn off the water supply and relieve the pressure first!

The anode rod was eroded but still had plenty of material left.

New aluminum alloy rod and old eroded magnesium rod

New aluminum alloy rod and old eroded magnesium rod

I wrapped the threads on the new rod with teflon tape and installed it. Then turned the fresh water supply back on and opened a hot water tap. Air was forced out of the hot water tank through the tap as the tank filled. Once I had a steady stream of water coming through the tap, I reset the breaker for the water heater electrical element. Job done! Twenty minutes later, I was ready for a hot shower and trip to Red, White and Brew for a cold one.

When I returned from the brew, Donna was pan frying potstickers and shredded cabbage on the induction cooktop for the weekly J Street potluck dinner organized by our neighbor, Jeanette. As usual, it was a fun time socializing around tables set up in our street.

The next project is to service the Spyder – oil and filter changes. We should have dry weather today with warm temperatures and clear skies. Tomorrow I’ll post a few pictures from Donna’s day kayaking the Salt River.

One thought on “Erosion and Corrosion

  1. FRAN

    WOW…thank goodness for happy hour. You certainly deserve it with all you do. Keeping that RV in great shape is mind boggling!

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