Stig1 · Dec 5, 2020

Just did a short run on the motorway and noticed the temp gauge dropping and just got home and the top to hoses going into the stat are hot and the one going to the bottom of the rad is stone cold its got the later style stat fitted

Nodge68 · Dec 6, 2020

Was the engine running at over 3000 RPM?

Stig1 · Dec 6, 2020

Nodge68 said:
Was the engine running at over 3000 RPM?

At times yes . Why ?

Nodge68 · Dec 6, 2020

Stig1 said:
At times yes . Why ?

Because it's a PRT (Pressure Relief Thermostat) fitted, which contains a pressure valve which is calibrated to open at about 3500 RPM. High engine speed will allow coolant to flow, even if the temperature sensing element hasn't opened. I've seen the pressure spring slacken off over time, causing the PR valve to open earlier than it should. With cold weather, coupled with high engine speed and a slack PR valve spring, over-cooling can occur, which seems to be what you were experiencing.

Stig1 · Dec 6, 2020

Nodge68 said:
Because it's a PRT (Pressure Relief Thermostat) fitted, which contains a pressure valve which is calibrated to open at about 3500 RPM. High engine speed will allow coolant to flow, even if the temperature sensing element hasn't opened. I've seen the pressure spring slacken off over time, causing the PR valve to open earlier than it should. With cold weather, coupled with high engine speed and a slack PR valve spring, over-cooling can occur, which seems to be what you were experiencing.

I think your correct im going to order a new one

Stig1 · Jan 18, 2021

New stat fixed it

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