Bongo Fury

Just replaced the temp sender on my Bongo and now seeing strange movement on the gauge. (Sender replaced due to no gauge movement after purchase a week ago)

If stopped and engine running, needle rises to 11 O'clock and stays steady.

As soon as I drive the vehicle the needle moves swiftly to the cold position and stays there. (Airflow through Radiator)

Other Symptoms:

Plugs looked black (Rich Running) on replacing
Heater warm but not hot
Mayonnaise in Oil filler cap

My question: Are the the above an indication that the thermostat has failed in the open position?

I would be grateful on any help or ideas to confirm my opinion.

Many thanks

Selwyn

Symptoms seem to match that. What happens if you blank the radiator with foil and take a drive? Ultimately, changing the stat should settle the issue either way, and changing a stat of uncertain age and unknown history, is never a bad thing. Buy a quality one though, don't skimp.

I would be more concerned about the mayonnaise on oil filler cap which could be a sign of an issue with head gasket(s) or other leak between cooling and oil systems. Do you have any details on the history of this vehicle?

Changing the thermostat is not a big job if you're handy with the spanners. Remove the engine undertray first to make access easier. You can see the housing just above the belt. Draining an replacing the coolant will give you the opportunity to check for signs of oil.

Many thanks to all who replied. As suggested, I blanked off the radiator.

The results are as follows:

Below 30 MPH temp gauge at normal position (11 O'clock)
Above 30 MPH temp gauge decreases to start of graduations.

There is no sign of Oil in the cooling water and the system does not over pressurise (confirmed with pressure tester). From evidence, looks unlikely to be a head gasket issue.

Looks like the thermostat is staying open and engine running cold. Glad it fails this way though

Further investigation and replacement of thermostat now to follow.

Sounds like blanking the rad made a difference (and you leave the foil there as a stopgap measure. A new stat seems like the thing to try, and hopefully that will sort it, and no harm done if not. Good luck, keep us posted.

I'll let the following pictures tell the tale





Many thanks to Simon at G P Autos of Harbury, Warwickshire. He replaced the Antifreeze, all the belts and the defective thermostat.

Bongo no longer running cool. Temperature gauge now showing normal operation.