Sobering measurements

[Graham_Wright]

Investigating the reason for reluctance of my engine to start when cold, I checked the voltage readings at the glow plugs. Battery volts about 13, at the plugs 10.7!

Most of the relevant cabling is Ø2.5 tinned or silver plated but the feeds are a bit long. Additionally, for control from the helm, the commands are buffered by relays.

By changing routes, I now have readings of 11.2 volts and the starting has improved. (As an aside, I monitor the heater current - fsd = four heaters and 1/4 fsd 1 heater.- very useful).

 

[savageseadog]

The cables and connections between battery and engine can't be too big or too well maintained.

 

[[70521]]

What type of engine is it?

 

[macd]

Investigating the reason for reluctance of my engine to start when cold, I checked the voltage readings at the glow plugs. Battery volts about 13, at the plugs 10.7...I now have readings of 11.2 volts.

Were those two voltages measured at the same time, or is the battery voltage when resting? It depends on your engine, but the glow plugs in a four cylinder can draw well over 20A, which is enough to substantially reduce the available battery voltage. A reading of 11V or so when the plugs are heating is not unusual.

 

[Graham_Wright]

The cables and connections between battery and engine can't be too big or too well maintained.

Core diameter 13mm! However, I haven't checked connector tightness. That's next.

 

[Graham_Wright]

Were those two voltages measured at the same time, or is the battery voltage when resting? It depends on your engine, but the glow plugs in a four cylinder can draw well over 20A, which is enough to substantially reduce the available battery voltage. A reading of 11V or so when the plugs are heating is not unusual.

Yes - they draw 6A each.

 

[Graham_Wright]

What type of engine is it?

BMC 1.5. I read here 60 secs preheat! It starts easily when warm but from cold, 1 cylinder, 2 cylinders and then the lot which lead me to compare heater currents.

 

[macd]

BMC 1.5. I read here 60 secs preheat! It starts easily when warm but from cold, 1 cylinder, 2 cylinders and then the lot which lead me to compare heater currents.

Had one of those, which responded to just 10 seconds glow, albeit with fairly new plugs and not always starting on all four.
For comparison I've been through the same rigmarole as you with a Land Rover. Obviously the battery is probably much closer to the plugs than on a boat, but 11.3V when glowing seemed typical.

 

[<152587>]

Seem to remember in the distant past the orifice that leads to the combustion chamber cokes up in these engines thus rendering the plug ineffective.

 

[Graham_Wright]

Seem to remember in the distant past the orifice that leads to the combustion chamber cokes up in these engines thus rendering the plug ineffective.

I think I reamed them but will check. Good point.

 

[dunedin]

We were losing a lot of volts on a recent engine setup - after much messing around turned out the battery switch was defective (some have a reputation for this)