Winterizing an RV in Southern California: Who Actually Needs It

Water does not split a line the moment the thermometer touches 32. It splits when enough of the water inside a fixed volume has actually turned to ice, and that takes both a lower temperature and time. The working threshold we use is 28 degrees or colder, sustained four hours or more, measured at the coach rather than at an airport weather station twenty miles away and a thousand feet lower. Water expands roughly nine percent as it freezes, and in a capped line that expansion has nowhere to go but outward through the weakest wall.

PEX tubing will stretch a surprising amount before it lets go, which is why the tubing is rarely the casualty. The casualties are the components that cannot stretch at all. A pump head, a brass elbow, a low point drain valve, a check valve body. Those hold a small fixed volume of water in a rigid housing, and they crack along a seam or a threaded boss where the wall section is thinnest. The split is frequently narrow enough that you cannot see it with the system dry.

The second variable is what the plumbing is sitting inside. An enclosed and genuinely heated underbelly buys several degrees and several hours of margin. An open frame trailer with PEX stapled to the underside of the floor buys nothing at all. Confirm which one you own before you decide, because plenty of units are sold with a heated underbelly where the heat source is the furnace, and a furnace does nothing after the propane runs out at two in the morning.

The mountain communities are not a judgment call. Big Bear, Lake Arrowhead, Idyllwild, Wrightwood, and Frazier Park all run multiple nights below 20 degrees every winter, and a unit stored there unwinterized will suffer freeze damage. Not might. Will. Those same units also carry snow load, which flexes the roof structure and cracks membrane at the truss lines, so a mountain-stored coach usually needs a roof inspection in the spring for reasons entirely separate from the plumbing.

The high desert is the band owners misjudge most. Victorville, Hesperia, Apple Valley, Lancaster, Palmdale, and Barstow sit at elevation with almost no humidity, and clear dry air radiates heat away fast after sundown. A November afternoon in Lancaster can reach 72 degrees and the same night can drop to 26. Owners see the daytime number, assume winter has not started, and get their first split around the second week of November rather than in January.

Coastal cities and the urban basin do not need it. A trailer parked behind a house in Costa Mesa, Long Beach, or Oceanside may see 38 degrees on the coldest night of the year, and the thermal mass of a full fresh tank never gets close to a problem. The low desert does not need it either, though Palm Desert and Indio owners have the opposite issue: a system that sat full through a 118 degree August grows biofilm and needs sanitizing, not antifreeze.

Storage location is only half the exposure. The other half is where the rig goes, and this is the case that produces most of the freeze damage we open up on units registered in Orange County. A coach that lives in Irvine and never sees frost at home goes to the eastern Sierra over Thanksgiving, or to the South Rim of the Grand Canyon, or to Bryce. The South Rim sits above 7,000 feet and runs into the teens on a clear November night. The rig has never been prepared for that, and nobody thought it needed to be.

Travel freeze protection is a different problem than storage freeze protection, because you still want running water. The practical approach on a trip is to keep the interior above freezing continuously, keep the fresh tank partly full rather than nearly empty so thermal mass works for you, disconnect and drain the city water hose every night, and pour a cup of RV antifreeze into each P-trap and the toilet bowl before bed. Then winterize properly on the drive home rather than after the rig has sat in the driveway for a week.

The failure mode that catches people on the way back is the dump valve. A gray tank with three inches of water in it freezes at the valve body, and forcing a frozen cable or blade cracks the flange where it bonds to the tank. That is not a valve replacement. That is a tank pull, and on a fifth wheel with an enclosed underbelly it means dropping the coroplast and the insulation to get to it.

There are two accepted approaches. Blowing the system out with compressed air, or pumping propylene glycol RV antifreeze through every fixture until it runs pink. The blow out method is faster and leaves nothing to flush in the spring. It also fails more often, and it fails for a specific reason: compressed air travels the path of least resistance and skips horizontal runs, dead legs, and anything with a trap in it. Air moving through a line at 40 psi does not lift standing water out of a level run under a dinette.

If you blow out, keep the regulator at 30 to 40 psi and never hand a coach an unregulated shop air line. RV plumbing is designed around roughly 60 psi working pressure, and a 120 psi blast will blow a fitting off a manifold before it ever reaches a fixture. Open one fixture at a time, hot side and cold side separately, and hold each one open until the air runs completely dry rather than merely sputtering.

The antifreeze method is more reliable because you can see the result. Pink at the fixture means the line is protected. It requires bypassing the water heater first, which is the step people skip, and a six or ten gallon tank will happily swallow most of a case of antifreeze if the bypass valves are set wrong. Propylene glycol is the only correct chemistry here. Automotive ethylene glycol coolant is toxic and does not belong anywhere in a potable system.

The ice maker supply is a quarter inch line that runs from a tee somewhere in the cold side, across the coach, and up behind the refrigerator. It is small, it is long, it holds water by capillary action, and it is behind cabinetry where nobody looks. When it splits, it does not announce itself. It drips a few ounces a day behind the refrigerator and into the floor, and eighteen months later there is a soft spot in front of the fridge and delamination showing on the outside wall in that bay.

The washer box on a coach plumbed for a combo washer is the same story with a bigger line. So is the residential style water filter housing, which is a rigid plastic canister full of standing water in a compartment that is not heated. So is the exterior shower, which is behind a hinged door on the outside of the coach with no insulation between it and the weather at all. Every one of these is a two minute job during winterization and a four figure job afterward.

A frozen split does not leak while it is frozen, because the ice that made it is still plugging it. It also does not leak while the system is dry, because there is no water to move and no pressure behind it. So the coach sits through February and March looking perfectly fine, and the owner concludes nothing happened. The damage is revealed on the first spring pressurization, usually the day the unit gets de-winterized in a hurry before a trip.

That is exactly the wrong moment to find it. The system goes to 60 psi on city water, the split opens, and water runs behind a wall or into the floor while the owner is outside stowing chairs. We see the results in April and May every year, and the water damage is almost always worse than the plumbing repair that caused it. A cracked pump head is a part and an hour. The subfloor it soaked while nobody was watching is a different order of job.

De-winterize deliberately. Flush the antifreeze out, then pressurize on the pump with the fresh tank only, not on city water. Let it build, then switch the pump off and watch it. If the pump cycles again on its own within ten minutes with every fixture closed, there is a leak somewhere in the system and you have just found it with two gallons of water instead of a garden hose running unattended.

Plumbing repair is billed at our mechanical and electrical rate of $260 per hour, plus parts. A cracked pump replaced with the bay accessible is typically one to two hours plus the pump. A split fitting inside a wall is a different conversation, because getting to it means removing an interior panel and sometimes cabinetry, and the labor to reach the failure exceeds the cost of fixing it by a wide margin. If a diagnostic is needed to find where the system is losing pressure, that runs $285 per hour with a one hour minimum, refundable as a credit against an authorized repair.

If the water reached the floor, you are no longer in a plumbing repair. You are in subfloor and substrate work, and that runs from a contained soft spot near a door up into five figures on a coach where the water tracked laterally and sat against the frame. Water in an RV is almost never where it came in, so the first phase of that job is metering the entire unit to map where the moisture actually traveled.

One boundary worth stating plainly: everything above is house side work. We do not handle engine, drivetrain, or transmission work, so a chassis coolant issue or a block freeze problem on a motorhome goes to a truck or chassis shop rather than to us. We also do not perform DOT inspections. All of our work is performed at our Yorba Linda facility.

A great many mountain and high desert owners solve this by not storing the rig where they live. A coach that spends the season in a lot in Corona or Chino instead of a driveway in Wrightwood never sees a hard freeze, and the drive up the hill in the spring costs less than one plumbing repair. The tradeoff is that the inland valley bakes it instead, so a reflective roof coating and covered storage matter more than they would at 6,000 feet.

If the rig has to stay up the hill, the highest value additions are an enclosed and insulated underbelly if the unit did not come with one, tank heating pads on the fresh, gray, and black tanks with a thermostat rather than a manual switch, and a small monitored temperature sensor in the wet bay so you know what the coach actually experienced rather than what the forecast said. None of that replaces winterization on a unit that is going to sit unused. It protects a unit that is in use through the winter, which is a different problem.