Cooling system "conditioner" for 2000 Forester

I don't have an engine with the gasket problem, but if I did then I figure the additive would go in with each coolant flush.

By the way, from what I remember reading about their "sealer", it isn't just a plug-type sealant but a heat-activated plug sealer. It's to plug leaks into the cylinder where is the higher heat.

One reader here in the past stated that the Subaru conditioner is actually Holts' Radweld. I didn't have a bottle to inspect.

a pic of Subaru's product "Holts" isembossed at the bottom of the plastic bottle so it's a dead giveaway. The claim is that this stuff "dissolves in the coolant and remains a liquid untill it is exposed to air and high temperature." The important word here is "and". Just exposure to air would mean it would plug any leak, like to the outside or even in the radiator or heater core. While it gets hot along with the coolant, that isn't hot enough. It takes the high temperature of the cylinder to activate the stuff so it seals against coolant leaks into the cylinder, not elsewhere.

They don't describe how it works. I found its MSDS at:

Alas, the MSDS only has to listcomponents considered hazardous so there can be ingredients not listedin the MSDS that are in the product. From the MSDS, disodiumtetraborate is borax which is acleaner (removes oxides). Phosphoric acid is also a cleaner and rustconverter is probably an emulsifier to meld the product into theethylene glycol (coolant) and used as a regenerator or booster; i.e.,this is the "conditioner" portion of the product. Ingredient list on the bottle: Ingredients listed on the bottle don't seem to match on Holts Radweld MSDS: see The resin is the air+heatactivated component. The linseed meal is a fibrilated fiber(particulate) suspended in the additive (and then in the coolant towhich the additive is added) that is used to fill gaps too large for theresin to handle alone "BACKGROUND OF THEINVENTION" section). The resin fills the cracks, the meal fills thegaps.

In the past, I found the following Subaru-sourced info on their coolant sealer, er, "conditioner", er, sealer+conditioner (SOA 635071):

Subaru "Endwrench" - Cooling System Conditioner Whenever the coolant is changed, you must add Genuine Subaru Cooling System Conditioner, (P/N SOA635071). It¢s been tested and approved for Subaru aluminum engines and radiators. Do not use aftermarket coolant reinforcement agents, sealers and/or flushing agents as those chemicals could corrode aluminum parts, or cause clogging. Genuine Subaru Cooling System Conditioner improves the efficiency of the cooling system and includes anticorrosive properties. When used as directed, it remains suspended in the radiator until the engine is started and thermostat fully opens. Once the conditioner begins to circulate throughout the cooling system, it is attracted to any suspected leakage area in the vehicle¢s cooling system. The heat generated by the engine acts as an activation agent and hardens the cooling system conditioner to help seal the area. Subaru of America, Inc. has determined that this product is safe for use in all Subaru vehicles."

So, yep, looks like you add it with every coolant flush. If you're going to add it, do so to new coolant; i.e., do a flush, put in the additive, and add the coolant. Don't waste it on old or reused coolant.

Below is some other Subaru info I found on which engines need their special "conditioner" (they don't like calling it a sealer):

For phase 1 engines, the leakage is internal hence destructive. Hydrocarbons show up in the coolant (detectable only with specialized equipment) and may appear as sludge in the overflow tank. Bubbles are seen in the coolant immediately after starting the car. Overheating can be erratic but most often experienced on slowing down or stopping after running the car at highway speeds for awhile. Owners have thrown lots of money at trying to resolve various symptoms, like replacing thermostats, coolant flushes, new water pumps or radiators. If overheating occurs too often or is severe, head warpage occurs and requires engine replacement.

Whether you have the destructive internal leak or non-critical external leak depends if you have a phase 1 or 2 engine.

Phase 1: dual overhead cam 96-99 Legacy Outback or GT 98 Forester or Impreza RS

Phase 2: single overhead cam 2000+ non-turbo Legacy & Outback 00-04 Legacy GT 1999+ Forester or Impreza 2.5

You sure you need the Subie conditioner? Doesn't your vehicle qualify as having a phase 2 engine? Phase 2 engines have an external leak so you don't need their special sealer, er, conditioner (but it probably works as well as other stop-leak additives). When you start the engine, the coolant that leaked externally onto the engine is too cold for you to smell, and when you start driving then you won't be smelling it. It's when the engine has gotten hot and you park the car when you smell the external leak from the coolant on the hot engine. For an internal leak (phase 1 engine) of coolant into the cylinder, you'd see white smoke out the exhaust and that's where you'd smell the coolant. Unless you had a rear hatch window/door open when you stopped, I'm not sure you're going to smell coolant coming out your tail pipe. Maybe you'd smell it when starting up and sitting there while the engine warmed up.

Whether it's an internal (phase 1 engine) or external (phase 2 engine), the Subaru rebranded Holts stuff probably works just as well for either engine type and leak direction; however, there are probably cheaper alternatives for an external leak. The real solution is to replace the defective gasket but, as you see, that's a pricey choice. Since you're probably only replacing the coolant (flush and replace) about every 5 years, the per-year cost difference for getting the more expensive Subaru conditioner probably doesn't amount to much. Personally I don't believe the claimed 11-year/120Kmile life cycle of Subaru's special coolant mix

on environmental conditions, I replace at 3-5 year intervals.I'd get nervous going longer than 5 years. The hygrometer you use tomeasure to the density of ethylene glycol doesn't measure the othercomponents (anti-rust, cleaner, oxidant, surfactant).

The conditioner does not work. Even on engines that Subaru claimed did not have a HG flaw (like our Forester 2002) its continuous presence starting at 31,000 miles did not prevent a failure ar 72,000 miles. If you already have a leak, there is absolutely no way it would help. But for $3 you may experiment and find out for yourself (while you are figuring where the $1200 will come from).

DK