Jump to content

2 random questions

Recommended Posts

I have had 2 questions in my brain for a while, mostly it's when I see it , it makes me wonder.

The first is regarding cooling fan thermal switches. I often see it recommended to put the sensor into the return from the radiator to the engine.
Why is that?
Wouldn't that have a colder reading?
I have mine in the top cover for my thermostat, above where the temp sensor for the dash gauge is.  my thought is when the thermostat opens and is circulating coolant through the radiator the fans turn on.... my temp gauge sits just a hair past the centerline even on a hot 100 degree day....

The next item up for discussion are those flex pipes I keep seeing get installed just after the exhaust manifold.. and I mean the real ones not those shit pipes to fix an exhaust....
I'm under the impression they are not really needed for a rear wheel drive engine do to the fact the motor rocks side to side vs a front wheel drive engine transversly mounted that's rocking front to back.. I'm sure there are other reasons,  maybe solid mounting the exhaust after the flex pipe I'm not sure...

I'm not saying this is right and everyone is wrong I'm just curious if any of this has some validity...

Link to comment
  • Replies 5
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

2 hours ago, Crashtd420 said:

I often see it recommended to put the sensor into the return from the radiator to the engine.
Why is that?

Im guessing here it give the actual temp of the water from IN the motor.


I always thought putting the therol switich on the bottom of the Rad before the intake back in the motor would be a good spot as one would now how cool/hot the water is in the rad. (so you know if rad is plugged up)



Edited by banzai510(hainz)
  • Like 2
Link to comment

Ginger?... or Mary Anne???? It's a good question. Think of the cooling system as being just below, just at and just above the turn on point for the sensor. Mine for example is 190 or 192 F I think. Factory thermostat begins opening at 180 F and fully open at 185 F?


I put mine in the return hose. This is the relatively coolest place so this is the coolest water returning to the hot engine. But not by a huge amount because the water circulating is through a fully open thermostat and high volume. So it is not going to be boiling hot inside and just reaching the sensor turn on point outside the engine. All points inside the engine and the cooling system, will be close to the same temperature. When the fan turn on temperature is reached, then the rest of the system is also maxed out and no further cooling can be expected without turning the fan on. This give the maximum time for the hot water in the rad to cool all by itself before reaching the turn on point of the fan. At idle eventually the fan turns on and remains on for 10 seconds. This is time needed for the rad to cool the water and circulate it down past the sensor threshold point and turn the fan off.  It remains off for 30 seconds, the time for the hot water above to work it's way down and turn the sensor on again. Driving in stop and go the fan may come on for longer periods but forward momentum also pushes air through the rad somewhat delaying the turn on. At highways speeds the fan never comes on unless climbing an extremely steep hill for extended time.


If the sensor were to be in the top radiator hose, it would react almost instantly to small temperature spikes and turn the fan on even though the rad is full of below temperature water that has yet to return into the engine. The slightly over hot water leaving the top of the engine has not been given the time to pass through the radiator and be cooled without the fan. At near the turn on point for the sensor, the fan will be turned on at times when not really needed.

  • Like 1
Link to comment

Temp sensor should be as near the thermostat as possible, but as many others have proven, it's not a deal breaker.


Flex pipes are good if you are trying to eliminate any resonance from the exhaust system. I build good hangers using OEM type rubber isolators, not those strips of tire used by muffler shops, and not those small blue round ones either. On a really low car, like a slammed 510 where the rear crossmember is a tight fit around the pipe, using hangers isn't always possible. That's when you would really want a flex pipe.

  • Like 1
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.