Diesel Doctor

[Tomk]

I bought an old boat a couple of years ago. At that time the glow plugs were working fine. A year ago, I too the head off it, had it reconditioned and refitted it. Soon after that, the glow plugs were burnt out. I replaced them with a set of PN-125s, which are supposed to be the correct plug for this engine. After 2 cold starts they burnt out. I replaced them them with a new set - same again. I have since put 5 sets of new glow plugs in, and each time cannot get more than 2-3 uses out of them before they are burnt out. The last time one of the tips was swollen, broke, and resulted in me taking the head off to get the broken tip. Don't want to do that again.
In and effort to fix the problem, I put a battery isolation switch between the relay and the glow plugs. I turn the switch on, glow the plugs for about 8 seconds, start the engine, and turn the isolation switch off, thereby cutting all power to the glow plugs. Same thing. 2 cold starts and these plugs are gone. They are 23V plugs. System is 24V.
Getting desperate here, any advice welcome. Thanks. Tom

[dieselmech2]

What kind of engine? There should be a glow plug relay or switch somewhere on the engine that will energize them. Even though you put a switch in there yourself it may be shorting them out since the old GPR is still in there.


Brian
Bleckman Diesel

[Tomk]

Hi Brian,
Good question - I edited my post and must have deleted that. Its an old Nissan ED-33. Marinised truck engine. Mid-eighties build I think. I placed the isolation switch between the relays and the GP - so when it is switched off, there is no chance of power getting to them. I have just dug a little deeper - the replacement plugs (ones available in the country) are HKT NP-125. They are a SQT plug. There are 2 other model plugs by that manufacturer, neither of which are available in the country. So I have ordered a similar plug from Bosch which will fit, which is a standard QT plug. 10-20 seconds and 800 deg C. I am hoping perhaps the change of plug might make the difference? The original plug in it was an NGK Y272R1 - but I am having a hard time tracking them down. So, I'm thinking perhaps it is a change in plug type causing the burn-out? (big maybe though...)

[dieselmech2]

Ok yeah I hope them work. That is fine where you put that switch, but what I am saying is that when the switch is ON it is letting too much through. See how the plugs work and let me know.

Brian
Bleckman Diesel

[Tomk]

Hi again Brian,
New plugs are in, so I will let you know how it goes over the next couple of weeks. I hooked a Fluke meter up to the GP circuit previously, and monitored the voltage to the plugs during the entire cycle - glowing, starting the engine, etc. At no time did the voltage get higher than 24V, even after starting, as I was only doing idling revs. Once started I turned the switch straight off. Just to be sure, I am now turning the switch (and therefore power to the GPs) off BEFORE I start the engine. In other words switch on power, glow, switch off power to GPs, start engine. Works well so far. We shall see how it goes after a few starts.
Many thanks for your replies to date. Tom

[Tomk]

Update - the new GPs are still working fine. Not sure if it is the change in model, or the fact that I am switching the circuit off immediately after glowing, but the problem appears to have gone away. Now I just need to locate an engine about double the horsepower to replace the current engine. (One of these days.....)
Thanks for you help on this Brian. Cheers Tom