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'95 Subaru Overheats At Highway speeds

My son has a '95 Subaru Outback that overheats at highway speeds but is okay around town. He’s replaced the thermostats, but that didn’t fix the problem. Sometimes the cars seems to lack power going up hills. Someone has told him that its the catalytic converter that’s causing his problem. Will a bad catalytic converter cause these problems?

A clogged cat can cause a loss of power, but I think the Check Engine Light would be on if that were the case.

Is this a 2.2 Liter or a 2.5 Liter engine? Is the engine losing any coolant?

He may want to test for leaking head gaskets.

He thinks its a 2.2 liter. No coolant loss that he’s noticed. He says the Check Engine Light does come on, but only when it’s raining.

There are a lot of possibilities including a radiator becoming coated inside with gunk, a failing radiator cap, a failing water pump (the impellars can erode and reduce the pump’s effectivity) and a breech in the headgasket. All of these can be checked by any competent shop.

By the way, the car is 14 years old…does anybody have any idea when the last time the coolant was replaced is?

The CEL will likely be a different cause, as that trips a code due to operating problems or emissions component problems, but that needs to be checked. Oh, and does anyone have any idea when the last tuneup was (wires, plugs, rotor, cap)?

The converter is highly unlikely to be the source of the problems. But I’m wondering of both problems are signs of neglect. No disrespect intended.