Generator set liner cavitation pits the coolant side of a wet liner until the wall perforates, and the damage is done before anyone notices. Check the specification against the coolant chemistry, then compare supplier offers before the first fill. Tesla Power writes the requirement on the plate; send the water report to the technical desk and we confirm it.
- Use a coolant with a nitrite or carboxylate reserve rather than plain water and antifreeze.
- Keep the loop pressurised, because pressure is what suppresses the bubbles.
- Bleed every air pocket, since entrained air is the fastest route to pitting.
- Test the coolant at every service and record the reserve rather than the colour.
What causes generator set liner cavitation?
The liner wall flexes slightly as the piston moves, and that flexing sends pressure waves through the coolant beside it. Where the pressure drops far enough, the coolant vapourises into small bubbles, and those bubbles collapse against the liner surface with enough force to chip the metal. Thousands of collapses in one place become a pit. A pit that is caught early is a liner that is replaced at the next overhaul rather than an engine that stops without warning.
The process is worst where the liner is thin and the coolant flow is slow, which is usually the thrust side and the area around the top ring travel. A pit that deepens past 1 mm becomes a perforation, and coolant then enters the cylinder or the sump. Tesla Power treats cavitation as a coolant chemistry problem rather than a mechanical one, because the metal does not change but the coolant does.
How does coolant chemistry stop it?
The additives in a heavy duty coolant form a film on the liner surface and raise the local boiling point, and both effects suppress the bubble collapse. Nitrite, molybdate and carboxylate are the usual actives, and the reserve has to be maintained rather than topped up with water. A coolant that has lost its reserve is plain water with a colour. The reserve is measured in the coolant rather than in the drum, so a fresh drum tells you nothing about the loop.
The reserve is consumed over time, faster on a set that runs hot and faster still where the coolant has been diluted. That is why the coolant is tested rather than judged by eye. Tesla Power specifies the reserve figure on the engine plate and asks for it at every service, because a drum of the wrong chemistry is worse than a drum of clean water.
| Item | Figure | Note |
|---|---|---|
| Glycol content | 50% by volume | Above 60% lowers heat transfer |
| Loop pressure | 0.9 bar cap | Pressure suppresses the bubbles |
| Additive reserve | From the maker figure | Tested, not judged by colour |
| Test interval | Every service | Sooner on a hot site |
Why does loop pressure matter?
A pressurised loop raises the boiling point of the coolant, so the local pressure drop beside the liner has further to fall before a bubble forms. A loop running at 0.9 bar is far better protected than the same loop with a failed cap running at atmospheric pressure. The cap is therefore part of the cavitation defence rather than only part of the cooling system. A cap that has lost its spring is a loop that runs at atmospheric pressure and pits a liner in a season.
Air entrainment works the other way, because air comes out of solution at the first low pressure point and adds bubbles that were not there. A leaking hose on the suction side of the pump draws air in without losing coolant, and a loop that needs topping up twice a week has one. Check the suction side for a weep and the cap for a seal before blaming the coolant.
What are the symptoms?
The first sign is often coolant loss with no visible leak, because a small perforation passes coolant into the cylinder and it leaves as vapour. A second sign is a rising iron figure in the oil analysis, because the pitted liner surface sheds metal into the sump. Neither sign points at the liner until the engine is opened. A set that loses coolant and leaves no puddle is the case that is misdiagnosed as a head gasket for weeks.
A borescope through the liner port or the drain plug can show the pitting before the perforation, which is worth doing on a set with a coolant loss it cannot explain. Tesla Power Equipment adds the borescope check to any investigation of unexplained coolant loss, because the alternative is to strip an engine that did not need it. A perforation usually appears on the thrust side of the liner, which is where the borescope should be pointed first.
How is the coolant checked?
Test the reserve with a test strip or a titration kit, read the glycol figure with a refractometer and read the pH with a strip. A reserve below the maker figure means the coolant needs an additive or a change. A glycol figure that has drifted above 60% raises the boiling point but lowers heat transfer, which is its own problem. A reserve reading taken on a cold loop and one taken on a hot loop differ, so record the temperature with the figure.
The volume matters as much as the chemistry. A 500kVA set at 0.8 pf delivers 400kW and holds about 40 L, so a 50% glycol fill needs 20 L of concentrate: 40 L x 50% = 20 L. A mix made by eye in a drum is a mix that is either weak or over concentrated, and both fail. Tesla Power records the mix on the loop drawing so a top up matches it.
What happens once a liner is pitted?
A pitted liner is replaced rather than repaired, because a welded or sleeved repair does not restore the surface the coolant film needs. On a wet liner engine the liner comes out with the piston and 4 bolts and the ring set, so the job is a partial rebuild rather than a service item. That cost is why the coolant is worth testing. A perforated liner on a set that has just been serviced points at a coolant change rather than at wear.
A set that has perforated a liner may also have hydraulic locked, which bends a connecting rod. If the engine stopped abruptly after a coolant loss, check the rod as well as the liner. Yangzhou Tesla Power checks both on any engine that comes back with a coolant loss and a hard stop, because the second fault is easy to miss.
What should a buyer put on the enquiry?
Send the engine model, the liner type, the coolant already in the set and the local water hardness. Add the duty cycle and the ambient, because a hot site consumes the reserve faster. Those six items let a supplier specify a coolant that protects the liners, and they show whether the offer has named a coolant at all. A coolant that is named by brand rather than by specification is a coolant that cannot be checked on arrival.
The wording on the offer matters too. Generator set liner cavitation manufacturers often quote a coolant by brand with no reserve figure, and Chinese generator suppliers sometimes ship a concentrate that is not compatible with the existing fill. Ask for generator set liner cavitation for a standby set, generator set liner for a mixed fleet and generator for a data centre as three separate cases. Tesla Power writes the reserve on the plate, and the 1000kW container build shows the liner arrangement.
What does the handover file record?
The file carries the coolant type, the reserve figure, the glycol percentage, the loop pressure and the test result at the last service. One page covers the coolant when those five items sit under the engine serial number. Add the conformity assessment for the coolant chemistry when the installation is part of a permit package.
Hand the page to the technician who tops up the loop rather than to the buyer who placed the order. the Yangzhou factory describes the bay where the coolant is mixed and tested. the commissioning notes lists the frames that use a wet liner engine, the build range explains how a suction side air leak is found, the ISO 8528-1 duty definitions sets the rating basis the duty cycle comes from, and the NFPA 110 maintenance routine covers the load steps the set was accepted on.
Frequently asked questions about generator set liner cavitation
It is not, because antifreeze protects against freezing and does not carry the additive reserve a diesel liner needs. A loop filled with water and antifreeze pits a liner within a few thousand hours. Use a heavy duty coolant with a stated reserve and test it.
A filter with an additive charge releases reserve into the loop slowly and is useful on a large engine. It is not a substitute for the right coolant. Check the filter at every service and replace it on the maker interval rather than when it looks dirty.
A small perforation passes coolant into the cylinder as vapour, so it leaves through the exhaust and nothing appears under the set. A pressure test on the loop that holds does not rule it out. Check the oil for coolant and borescope the liners before stripping anything.
It is far less common, because there is no coolant directly against the liner wall. The same coolant chemistry still matters for the head and the water pump. Read the engine type before applying a wet liner rule to a dry liner build.
It lasts to the major overhaul, which on a standby set can be many years. The liner is not the limit when the coolant is right. The limit becomes the ring set and the valve seats, which are service items rather than rebuild items.
A test strip costs very little and takes a minute, and a laboratory sample costs more and tells you about the wear metals at the same time. Either is cheaper than a liner. Tesla Power recommends the strip at every service and the laboratory sample once a year.