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Engine temp - new thermostat


bartenderfloyd
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Hello all! 1950 Plymouth Special Deluxe.  I changed the thermostat yesterday and took her out for a ride today.  I haven't driven her for a while so I don't remember where the temp gauge sat but it was not this close to the hot side of the gauge (see pic below).  I took out the old style thermostat and replaced with a 180 new style (pic below, old one on left, new one in pieces on the right).  Is this getting too close to the hot side?  Should I switch to a 160 or back to the old style even?  During the ride it was hovering over the "M" and it moved just over the "P" while idling in the driveway.  It's only 75 degrees outside.  What do you guys think?

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just wondering,,  is the old Tstat is a by-pass style and the new one isn't???  I think the thermostats housing are not the same,,  on my 251 , I have a newer style,, like the one on the right, Here are the different style,  first by-pass and second regular,, but I forgot to mention my 251 in my Dodge is an Industrial engine, maybe that's why I have a regular housing???,

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2 minutes ago, plymouthcranbrook said:

On my 52 non bypass style the bypass style thermostat would not fit in the housing.  I did not know about the differences at the time I did yhst.

When I bought my 51 Dodge Crusader, I thought it was a  long-block 218 cu in    so I should had the by-pass housing,  I did worry for awhile,  but  I saw the label on the side of the block ,, ''Industrial engine 251 cu,in.''  and of course because of the great help on this forum, I find out my set-up what ok,, never overheat in 3 years.  But next year, I will do the 3 engine/trans  mounts replacement, timing cover gasket & seal,  and of course the full cooling system maintenance as per the shop manual..  

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1 hour ago, lepic56 said:

just wondering,,  is the old Tstat is a by-pass style and the new one isn't???  I think the thermostats housing are not the same,,  on my 251 , I have a newer style,, like the one on the right, Here are the different style,  first by-pass and second regular,, but I forgot to mention my 251 in my Dodge is an Industrial engine, maybe that's why I have a regular housing???,

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Pretty sure it is a bypass.  The housing looks like this one on top.  When I pulled the old thermostat it was all loose, unlike any thermostat I've ever seen.  I could move the spring up and down with a minor push.  Plus it had a hole drilled through the top (a trick I did on my corvette before those holes became standard on a 160 thermostat).

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Just took her out for a half hour drive.  This is where the gauge sits while driving.  I checked the temps with the laser temp gun and at the thermostat housing it was 177 degrees and in the rear of the engine 181 degrees.  I then let it sit idling for a few minutes and the gauge went back to the position I was worried about.  I took the temps and the thermostat was 195 degrees at the thermostat housing and actually a few degrees less at the rear so I think we are all good.  Thanks for the advice.

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But you don't know how accurate the gauge is.  If your infra temps

are what they say they are, seems like no reason for concern.   Remember the thermostat temp rating is when it begins to open to circulation coolant to the radiator.   It has little effect on operating temp when the system is fully off bypass.

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7 hours ago, bartenderfloyd said:

Just took her out for a half hour drive.  This is where the gauge sits while driving.  I checked the temps with the laser temp gun and at the thermostat housing it was 177 degrees and in the rear of the engine 181 degrees.  I then let it sit idling for a few minutes and the gauge went back to the position I was worried about.  I took the temps and the thermostat was 195 degrees at the thermostat housing and actually a few degrees less at the rear so I think we are all good.  Thanks for the advice.

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the red statement above is indicative of low airflow through the radiator when idling.   Unless you idle a lot, or it continues to climb when idling that is normal.   The cure, if you want to pursue it would involve improving the idle airflow, either by using a better fan.  I assume you have the normal 4 blade version..  There are several versions with more blades that will fit.  Or add a electric fan controlled by a thermostatic switch so it only runs when needed.'

 

My plan is use only an electric fan, maybe two set to turn on sequentially if temps rise.

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Reading too hot for me...

A normal reading would be just beyond the "E".

If you can or want to...test the gauge with accurately heated water say to 180 and also 212 so you know what the gauge reads at those water temps using a small heated pan/ can of water.

I have always done that on questionable temp gauges.

Pulling the bulb out of the head might be easy and come right out or the core plug above it will need to be removed enabling the temp bulb to be wedged out.

All this to be sure of a accurate gauge.

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Just go to the dollar store and get a kitchen thermometer.   Run it up to operating temp with the radiator cap off, then take the coolant temp in the radiator.  This will not be 100 % accurate because it isn't getting temp from the hottest point in the engine but you should now know within 10 degrees what you gauge is indicating in the position where you get any.  Also remember 50 50 coolant mix has a raised boiling point.  What does the jug say the. Boiling point is? I think around 235 degrees, so there is wiggle room at 190 of 30 degrees in stead of 22.  Also coolant temp will always rise after shut down or with extended idle. As both air and coolant circulation rates have both slowed down.

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On the big Desoto I took the thermostat housing and drilled and tapped the side and stuck in one of those little moon thermometers.

 

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That way I can always cross check it against the dash gauge. Simple, effective and less than $100 for cheap insurance as to engine temp.

 

James

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