Piston Slap: Rubber Fetishes and Blowing Your Lid

John writes:

How often should coolant hoses be replaced on older vehicles? And not just when they start to leak! Should it be based upon age, mileage, climate of operation, or what? For that matter, what about the other hoses conducting pressurized fluids, vapors and the like? We have guidelines for belts and serpentines, but hoses?

Sajeev responds:

Good question. I’d check coolant hoses at every coolant change interval, which also leads to the obligatory RTFM reference for the newbies. Squeeze the hoses (when cooled, obviously) and look for brittle, soft or cracked rubber. Maybe go to a parts store and fondle a new hose to make sure you know the difference between a good hose and a soft one that’s about to burst. Don’t be shy!

And don’t forget the smaller hoses feeding coolant to the heater (at the firewall), the water pump and your overflow bottle. Every hose is critical on a pressurized system, if one fails the whole thing goes kaput.

Regarding other hoses: like transmissions (I’m looking at you, various iterations of the Chevy Malibu) that don’t come with a dipstick, other hoses are made to last “the life of the car.” Automotive leasing aside, that’s a crock. You will have to address these hoses after 8 years or 100,000 miles. The most common hose failures surround emissions equipment like the PCV system, and miscellaneous intake manifold mounted vacuum lines/junctions that cause “Check Engine” lights and poor performance.

And from what I’ve seen on the forums, these trouble codes (engine bank lean codes, specifically) are a ruthless/ignorant mechanic’s wet dream: there’s money to be had by throwing parts (and labor) to chase down a code instead of ruling out the most obvious problem. So do yourself a favor and inspect all hoses when you do a tune up, or change an air filter.

NN writes:

My 1998 Chevy Blazer (ZR2, 4wd, 5-speed) with ye olde 4.3L pushrod V6. 145k on the odo with recent radiator, water pump replacement. I had the coolant flushed and switched from the old Dexcool to the regular stuff. I noticed this past fall as the weather cooled that the engine was never really warming up…staying cold all the time, so I put in a new thermostat, figuring the old one was stuck open. Then the weird stuff started happening…sometimes my new thermostat wouldn’t pop open until the engine temp got well above 210, and I got a little nerve wracked.

It’s not the gauge… feeling the upper hose and seeing it was cool told me that it wasn’t circulating. Eventually the t-stat would pop open, but not at a consistent temperature; and well above the halfway mark where it should open. At the same time, there was a small coolant leak coming from somewhere I couldn’t detect… I guessed the leak may be a bad freeze plug, and a bottle of Bars stop leak did the job and sealed the leak. I switched out the thermostat again thinking the first new one was bad, and that didn’t work-same issue. I then figured the reason the thermostat wasn’t popping may be a lack of pressure in the system so I got a new radiator cap. Since the stop leak and the new cap, I haven’t had the thermostat issue.

But the heater is still weak, which leaves me with a lack of confidence. Did I really fix it with just a new cap and a bottle of stop leak? Could it have been a lack of pressure due to a worn cap or small leak that led to the delay in the opening Thermostat? Or could it have to do with something else (heater core?) that I’m not considering? I’m not sure I’m out of the woods yet so any other ideas would help.

Sajeev reponds:

Nice detail in your write up. I think you are out of the woods: the radiator cap was the final solution to your complex problem. For paranoia’s sake, check your overflow tank for stress cracks. Depending on the vehicle, an overheated (plastic) reservoir can lose its marbles and leak, which leads to engine overheating. Or on an I-6 BMW, a warped head and a $13,000 repair bill. Hot damn!

The heater is a mystery to me, perhaps it was clogged and the stop leak plugged it shut? I’ll keep my fingers crossed that replacing the heater core doesn’t involve removing the dashboard in the Blazer. I’m doing that right now and it truly sucks.

[Please submit your mechanical quandaries to sajeev.mehta@thetruthaboutcars.com]