Pete began work on our 1989 Daimler Double Six by starting the engine and checking the coolant level, which was then topped up. With the engine running, the vehicle was raised on the ramp and brought up to operating temperature to inspect for any signs of coolant leaks. None were identified during this process. The coolant system caps were examined, revealing a slightly damaged seal on the header tank cap. Replacement caps were ordered as a precaution. The heater function was also tested for both hot and cold operation, and hot air was successfully detected at all vents as commanded.
To further assess the system, a vacuum test was carried out via both filler caps. When the tester was applied to the centre cap, the system struggled to maintain a full vacuum, although it did not lose pressure at low levels. However, when connected to the header tank, the vacuum held perfectly. The coolant level was rechecked, and both caps were refitted.
An extended road test was then conducted, confirming that the temperature gauge maintained a stable reading and the cooling fans operated as required. Upon returning to the workshop, the car was left to idle in order to observe heat soak behaviour. The engine remained at the correct temperature, and after shutdown, the cooling fan continued to run and completed its cycle correctly before shutting off. No faults were found in the cooling system aside from the minor damage to the cap seal.
The next morning, after the car had fully cooled, the coolant level was checked again, and approximately one litre was added. No evidence of fluid leaks was found under the vehicle or around the engine bay and associated pipework.
A further 30-minute road test in mixed, rush-hour traffic was performed. Throughout this test, the vehicle displayed no signs of cooling issues. The engine maintained a stable temperature with no performance loss, misfiring, or symptoms of head gasket failure. Following the test, the car was allowed to idle at 1500rpm for ten minutes. As expected, the temperature rose slightly but remained only just above 90°C, with the cooling fans operating correctly. Once the engine was switched off, the fans continued their cycle and shut down appropriately. Pressure within the radiator pipes remained within normal parameters, and airflow through the fans was confirmed to be effective. The cooling system showed no indication of any leaks.
It was noted that once warm, the engine oil pressure dropped slightly, though no warning light was triggered. This suggests the oil becomes thin at operating temperature. Pete recommended an oil service and replacement of the auxiliary belts, particularly as the existing belt appeared aged, to ensure reliable fan drive operation. The air conditioning system was also checked to rule out any confusion between a potential leak and water from the condenser; the AC was found to be non-functional.
Ultimately, the fault described could not be replicated under any of the test conditions available. It is likely that the issue arose from an incorrectly fitted cap at the time of the reported fault.
