......part: 165473.....am I buying the best thermostat for my 355 M2.7? I heard somewhere that these OEM parts do not operate correctly...or is this a myth?
Are you telling me that you believe that there is one spring better then another?? Thats all there is to a thermostat.. if you have any doubt if its going to work.. put it in some boiling water and watch it work.. then install it.. that's about as simple as it gets!!
Looking at the specified application of the 355 thermostat ..... it is also used on the Mondial and 348 Not taking cabin heater configuration differences between these models into account ..... there must be a reason(s) why this particular thermostat, often has difficulty keeping the 355 engine within an acceptable operating temperature. Manufacturing variability or defects tend to reveal themselves when a component is operated at or near it's limits ..... the 355 engine because of it's higher compression, increased breathing capacity and higher RPM range ..... does generate higher heat loads a little more quickly than the 348 or Mondial ...... this may over extend the thermostat's mechanical ability to timely respond to and control the quick temperature changes, causing premature wear? ...... however this in and of itself should not be a problem at all for a 'normal' thermostat ........ but it may partially explain the long list of thermostat longevity variations I have seen on many 355s ..... and ..... not so much on 348s ....... hmmm Ok .... now ... BUT!!! ....... that higher heat load of the 355 would only be part of the story ....... this same thermostat which previously only saw heat generated by the engine in the 348 and Mondial .... now sees the addtional heat load of the 355 transmission cooler ...... this can very well create a temperature discrepancy ....... because the thermostat is located after the transmission cooler ..... the thermostat will open sooner than it would, had the trans cooler not been there .... in other words, the thermostat thinks the engine is at a higher temperature than it actually is ...... so it opens .... and causes the engine to run cooler than the thermostat temperature rating .... the ECU sees the cooler engine temperature and responds with a richer mixture (which we know the 355 is known for) ........... then factor those pesky manufacturing variations or defects in the thermostat .... and things can go even further down hill from there ........ Illustration below shows the 348 coolant pump/plumbing assembly (note part 40) ........ Illustration further below for comparison, is of the 355 coolant pump, with the additional trans cooler assembly (note part 51). Image Unavailable, Please Login Image Unavailable, Please Login
I think you nailed it the thermostat sees a higher temp because of the transmission and stays open more than it should eeping engine cooler.
All I know is that my 308 and my 355 temperature behave almost identically on a day of similar ambient temperature and in similar traffic. Also note that the coolant temp sensors with influence the ECU/mixture are located before the trans oil cooler.
precisely..... !! ........... the coolant temp sensor will read a lower temp than what the thermostat is rated at and is responding to ....... cooler temp sensor = richer mixture ...... This at minimum, partially explains why so many 355s are reading lower than ideal coolant temps ..... as clearly indicated by the poll thread in my signature ......
