Mack MP8 SPN 111 FMI 1 — Coolant Level Low

Code Details

Plain-English Meaning

The Mack MP8 cooling system uses a coolant level sensor in the deaeration tank to monitor the coolant level and alert the ECM when the level drops below the minimum safe threshold. When SPN 111 FMI 1 is set, the driver is notified through the instrument cluster and maintenance is required to determine whether coolant loss has occurred and identify the source. The MP8 is a heavy-duty diesel engine used in Anthem, Pinnacle, and Granite vocational models that operate under demanding load conditions — conditions under which adequate coolant volume is critical for managing the high heat output. External coolant leaks from hose connections, the radiator, or the water pump are the most common causes of coolant loss. Internal leakage through the head gasket or EGR cooler is less common but should be investigated when no external source is found. A sensor or wiring fault can produce a false reading and should be ruled out once the physical level is confirmed.

SPN 111 is Coolant Level; FMI 1 indicates a valid signal below the normal operational range. On the Mack MP8, the coolant level sensor monitors the deaeration tank level. Mack Premium Tech Tool (PTT) provides the sensor live status and freeze-frame data at fault set. PTT should be used alongside a physical coolant level inspection — the tool confirms sensor behavior, while direct inspection confirms the actual level. If SPN 110 FMI 0 (high coolant temperature) is also stored, the coolant loss is affecting thermal management and the situation is more urgent. PTT cooling system data can help identify whether the temperature has been elevated alongside the low coolant level.

Common Symptoms

• Low coolant level warning on the instrument panel
• Coolant deaeration tank visually low or empty
• External coolant seepage at hose fittings, radiator, or water pump
• White exhaust smoke or coolant odor from the exhaust if coolant is burning internally
• Coolant temperature rising if the cooling capacity is compromised

Possible Causes

Possible causes may include the items below. The list is not a parts diagnosis.

• External coolant leak at hoses, fittings, or clamps
• Radiator core or tank leak
• Water pump seal or weep hole leak
• Head gasket failure causing internal coolant consumption
• EGR cooler internal failure causing coolant to enter the exhaust
• Coolant level sensor or wiring fault causing a false low reading

First Checks

• Inspect the deaeration tank and radiator coolant level with the engine cold before operating
• Look for visible coolant leakage at all accessible hose connections, the radiator, and around the water pump
• Add the correct pre-mixed coolant to bring the level to the full mark and monitor the level over the following hours of operation
• Connect Mack PTT to check the coolant level sensor status live and confirm the sensor reading matches the physical observation
• If no external leak is found and coolant continues to be lost, perform a combustion block test and inspect the engine oil for emulsification indicating internal coolant leakage

Can I Keep Driving?

Low coolant is a serious cooling system condition on the MP8. Avoid high-load operation with confirmed low coolant. The risk of rapid overheating is significant during heavy vocational work or linehaul operation with insufficient coolant volume.

Related Lookup Pages

• SPN 111 topic page
• FMI 1 explanation
• Search this code