Heater bypass not the cause of rough running

Dear Car Talk:

My heater core started leaking, so I plugged the hoses going to the heater. I live in Hawaii, so I don’t need the heater. After a few months, I noticed that the plugs I had installed had started to crack. They’re not the same-quality rubber as the hoses. So, I replaced the plugs with a hose that just connects the coolant line going to the heater core with the coolant line coming from the heater core. Then I started to notice that the car runs rough in traffic. Did I do this wrong?

— Charles

“Don’t need heat.” Sure, rub it in, Charles!

You did it exactly right. You basically take the two hoses off the heater core, you stick them together and you’re done. That way, the coolant will continue to circulate, even though it no longer goes through the heater core.

And bypassing the heater core should have no effect at all on the performance of the engine, Charles. So there’s something else wrong that’s causing your rough engine operation in traffic.

What else did you “fix” recently, Charles? I’d start there.

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