Originally Posted by fish head
I know nothing about Duramax diesels but ...

I was having a problem with my gas 98 Chevy taking longer than normal to warm up and it turned out to be a faulty radiator cap. It was only holding 13 psi instead of the required 16 psi. I would never have believed that a slight difference in pressure would make a difference but it did. Pressure and heat go hand in hand.

My first thought was a bad thermostat so I put in a new one but no change. Then I swapped out the radiator cap and that cured the slow warm-up problem.

Just to play scientist for a minute...water can't get any hotter than boiling. At normal pressure, it boils at 212 and that's as hot as it can get until it turns to steam. As the pressure rises, the boiling point goes up.
So, at 13lb, you have a certain boiling point. At 16lb, the boiling point is higher.

Once water turns to steam, the pressure will skyrocket and can become very dangerous. The purpose of a thermostat is to keep the temp below the boiling point and one of the purposes of the radiator cap is a fail safe to release steam before it blows up something if the thermostat fails.


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