glow plug questions

[apm]

I've got a Komatsu PC50UU-1 with a 3 cylinder komatsu engine. Always been a slow starter, in cold weather requiring a sniff of starting fluid. I finally got around to testing the glow plugs and found 2 out of 3 not working. I've gotten 3 new ones to install, today. What is the rule of thumb for time for preheat? I turn the key backwards to energize the glow plugs. Do I wait 15 seconds, 30 seconds or what. I know not to use ether after preheating. Does too long of "on time" burn out the glow plugs? Can I cycle them once, try to start and if no start is there any advantage to cycling them again?

Thanks,
Greg

 

[Randy88]

Greg every engine is different in what it takes to get them to go and how cold out it is, I'd start at about 20-30 seconds and if it doesn't start try it again. I have a komatsu pc75 with a four cylinder engine and that's how I go about it, some of my other engines have preset seconds they'll heat till they shut off, and if it won't start I just recycle them again and try to start the second or third time.

As for too long of on time burn them out, not really, we've had glow plugs go bad and it doesn't matter if we use them every day or not at all to only seldom, you just never know what causes them to quit working for sure, we usually get several thousand engine hours out of glow plugs on average before we need to replace them, but it depends on the engines application and how often its started.

 

[apm]

Thanks for the fast response! I just changed them out and taking your advice, cycled them for 20 seconds. It fired right up on the first try. It's about 30 degrees, here. I think I'm going to like having working glow plugs!

Greg

 

[dakuch]

On ours Hitachi you turn the key on and wait for about 20 seconds and light goes off and your ready to go. I bought our machine and 2 were bad of 3. I added a blade type fuse in line, cause one shorted out and melted safety link. Was hard to find, down by the starter battery connection. This way very easy to check if power is going to glow plugs.
Good luck