I was helping a customer the other day who requested a heat exchanger tube stack for an M753K. This is a 10 year old generator, but I was still shocked that he needed a heat exchanger. In our experience, the only thing that can cause a heat exchanger tube stack failure on a 5-20 kw generator is very poor maintenance. When I looked up the part number for the tube stack I noticed that we had sold 3 in the last 12 months.
There are, conservatively 300-400 of these generators in operation in the Caribbean, so that works out to less than a 0.75% failure rate. Most of our competitors would be envious of such a low failure rate, but we still feel that is too high. The only reason that these tube stacks are failing is because of poor maintenance practices, or using the wrong coolant.
We need to educate our customers that the only proper coolant is Distilled Water, or a 50/50 premix ethylene glycol mix. If our customers want to use 100% ethylene glycol, they need to dilute it with 50% Distilled Water. Most of the water we get in the Caribbean comes from Reverse Osmosis, and that often leaves too high a mineral (including salt) content. Even with proper coolant, sludge, scale and corrosion build up over a period of time. So we recommend that our customers drain, flush and refill their cooling system every year as part of their annual maintenance.
If the customer wants to extend the coolant change interval, they should purchase a pack of coolant test strips (part number 20-00005) and test their coolant every 6 months past the 1 year anniversary of the last coolant change. The coolant strips cost $15. A tube stack costs nearly $500.
In addition to the tube stack failing, poor coolant quality can cause water pump failure, and the core plugs (water jackets) to corrode from the inside out. Made of a thinner, less corrosion resistant material, the core plugs can often be the “canary in the coal mine”. If they start to leak, the customer knows he has a problem. A bigger problem is that some of these core plugs can be very hard to get to in order to change them.
So we need to emphasize to our customers that it is a very good investment to change their coolant every year, even if they need to hire their local dealer to do so. It can save them a lot of money down the road.