Do I need to replace all 4 glow plugs if one is broken?

[SanAlan]

Do I need to replace all 4 glow plugs if one is broken? The following is the relevant introduction of glow plugs: 1. The function of glow plugs: Glow plugs are used to preheat the intake air when the diesel engine is started at low temperature. Using glow plugs in winter can shorten the starting time, reduce the current consumption of the battery and reduce the wear of the diesel engine. 2. Cold engine power-on: When the engine is cold, power the glow plugs for 2 minutes, and touch the electrode of each glow plug with your hand. If the heating element of the glow plug is disconnected, the electrode will be cold. This method is simple and easy to implement, but the effect is slightly worse. 3. Single test: Test each glow plug individually, remove each glow plug, ground the outside of the glow plug, connect the live wire to the glow plug terminal F (use 12V power for vehicles with 24V batteries), and conduct a short-cycle test. If the glow plug becomes hot, it means it is intact.

[MaximusRose]

I've been driving a diesel car for twelve years, and when a glow plug fails, don't just replace the single faulty one. These little guys are usually installed in the same batch and have similar lifespans. Just like changing tires, it's more cost-effective to replace all four at once. My old car learned this the hard way—last winter, one plug failed, and I replaced just that one. Within two months, the other three failed one after another, leaving me struggling to start the car for half an hour in the cold. The mechanic later explained that the new plug's resistance didn't match the old ones, which actually harmed the battery. Since then, I've been replacing the full set, and three years on, everything's been fine. In the end, it's cheaper than dealing with three separate replacements.

[StPaige]

Last time my diesel pickup had a glow plug warning light, the mechanic advised me to replace all of them as soon as he opened it up. He said these parts are all from the same production cycle with identical lifespans - although the remaining three still work now, their internal resistance values have long exceeded the standard. The heating efficiency difference between new and old plugs can reach 20%, causing uneven cylinder heating during startup that damages piston rings. The most crucial factor was labor costs - replacing one requires removing the entire manifold, costing 400 yuan in labor, while replacing all four only adds 100 yuan more. Spending an extra 600 yuan on parts saved me the hassle of repeated disassembly later. Thinking back, it was totally worth it - this year at -15°C the engine still starts perfectly at first crank.

[MacBradley]

As the logistics manager for the fleet, I've seen too many cases where replacing just a single glow plug backfired. Last week, a stubborn driver insisted on changing only one, and within half a month, two spark plugs burned out. Now we have a standard procedure for replacing kits: first measure the coil resistance of all four plugs—if the variance exceeds 15%, we recommend replacing the entire set. New plugs and the ECU module have an automatic adaptation period, and mixing old components can easily cause preheating duration irregularities. Honestly, saving a few hundred bucks isn't worth it—when it fails on the road, the towing fee alone will cost more than the parts.