Fifteen PSI! If you rupture hose from 15 psi it must have had some kind of syphillis bump on it for 5 years already!

If you raise boiling point of coolant, you can increase temperature of coolant which is desirable...

don't forget the temp of coolant is not equal throughout, if you see 90 C at head outlet, you might have more in localized spots, you don't want boiling in any point as cavitation can eat metal...

Reviewing all your posts on this thread we as individuals have some simularities. If an engine is running hotter than an average example of the same model is I too want to know why.

A hotter engine experiences less wear and is better from an efficiency perspective. The only problem Is I want the engine operational temperature elevated by my choice of a higher temperature thermostat.

You might consider letting go of this until the warmer weather arrives. If it will not blow its coolant out under any situation then I might just let it be.


It was good to see you refilled the system properly. Trapped air in my opinion does not move but creates a hot spot in the area it is located in. Enough air and the coolant could blow out as any fluid getting to that area may boil.

This engine has the cast iron head as well. So much less concern there than the fragile early aluminium heads on the later engines. Basically as long as there is coolant staying in the 616 or 617 engines will do no harm. Unless you are certain otherwise this particular car may have always been the same. Make sure to have a look if you have not already for any bubbles appearing in the expansion tank.

For yourself and anyone else reading this thread, the FSM is absolutely correct. Anyone suggesting to test the vehicle without a thermostat installed doesn't understand how the system functions and shouldn't be offering up advice that is wrong.

I run a 10 degree lower stat,plus with one holed drilled for air release. I the summer a stat with bunches of holes.These motors are old and need block soaked in acid to get rid of scale.

The 617.95 engine features a bypass passage integral to the thermostat housing. With that in mind, drilling holes in thermostats makes no sense whatsoever.

i believe its clogged.
took forever to blech air before.Now bleeds air and you can fill one time.

Details.........we need details of this "unclogging".........please.

Or, did you fail to solve the clogged line and simply drilled the 'stat as a solution (albeit a poor one)?

I appreciate all the help, advice, and suggestions so far.

I'm going to try a known-good thermostat and see what happens with the temperature. While I'm not overly concerned with the current temperatures, I'm hoping to get it down at least a little.

I figured I should update this thread.

I purchased a known-good thermostat from qwerty (thanks) and installed it last Saturday. I have been using the car every day for a week now in a wide variety of temperatures (28F to 75F) and at the temperature has never risen above the 9 o'clock position on the gauge (about 88C). The gauge typically shows between 80C and 85C, so I'm very happy to be back to where I should be with regards to engine temperature.

So, it appears that the two brand new thermostats I purchased and tried initially were both operating at the upper end of what I assume is their margins of error for manufacture.

Thanks for closing the loop on this one. It is frustrating that we cannot trust new parts to operate correctly. I am glad you found the solution.