best place to install water temp sending unit??????????

where is the best place to install the water temp. sending unit... the head or intake???
I have been told tht the intake will be 20-50 degress cooler than the head actually is,
and if you put it in the head the sending unit will asorbe the header heat at slow or idle speeds giving you a flase high reading!!!

so I am really confused!!!!!!!!!!! i just want the most accurate reading so I do not fry the motor.

also what is highest safe temp for a motor at idle.

I have a 454bbc that is running 225@ idle with a electric sending unit in the head. is that too high or is it alright?????

I live in a place where 120 degree days are not uncommon at this time of year with little humidity. I'm continually told that outside temp plus 100 degrees is not unexpected on a modern car equipped with a thermostat,fan clutch, and/or thermostatically controlled electric fan....
Having said that, I'm usually able to get almost any of my chevies to run under 200 (160-180 at speed) with the following improvements:
1) A new 3 or 4 core radiator... cheap from Auto Zone or Checker
2) A new 160 or 180 degree stat.... be sure to heat water in a coffee cup to expected temp and test! I've been told that over 35 percent of new stats are bad!
3) Replace the fan clutch with a solid spacer, but keep the stock fan..... The sound it will make at speed will remind you of a helicopter or prop plane booting up for liftoff or like your trans may be slipping (it isn't). Folks say it will cost you horsepower and fuel mileage, but I haven't been able to prove the mileage loss thru careful testing. What I can gaurantee is reasonable temps and cold a/c even when idling at a drive-thru!
If you do those three things and your 454 still won't run cool, try replacing the water pump and completely removing the stat.
Once you get to this point the coolant will be circulating continuously without interruption. Auto parts guys are always trying to tell me that the coolant doesn't spend enough time in the radiator to cool, to which I reply that it spends comparatively less time in the engine being heated, as well. In practice, your engine will simply run cooler without a thermostat and you'll have one less potentially problematic part to ruin your day.... same for the fan spacer!
If you then are still running hot, you have cam timing, ignition timing, or carburetion issues, or are running too much compression or have bored the engine too big. Another thing to check when cold is if any of your cylinders blow antifreeze, which would indicate blown head gasket or something cracked.
To answer your sender question...
I really prefer to use the bungs in the intake manifold because the coolant present there is from both sides of the engine. An argument for using the head bungs is more accurate head temp with less possibility that the coolant level would ever be low enough to leave those locations high-and-dry. Many of the current manifolds have multiple bungs and I like to plumb in a mechanical temp gauge to verify the electric one.

Hottroddd57,
If you are worried, you could invest in three senders and put one in each head plus one in the intake manifold. This would allow you to run a test to see what the offset is between each location. It really doesnt matter where the sender is located after you have a baseline....you want to look for changes from normal....whatever normal is. For instance, if your gauge reads 205 deg in normal summer traffic and one day, it goes to 235, you are alerted to something changing for the wrong......that's why a lot of gauges dont have numbers....so people dont get caught up with the number and they will react to the change.

A common error in gauge mounting is to use a pipe adapter that shrouds the sensor probe end. For engines that mount the sensor vertical, the pipe adapter (bushing) can trap air around the sensor tip and theoretically affect the reading by insulating the tip. I usually try to find a bushing that allows the tip to be extended a tad.
that's my story and I'm sticking to it.
mike in tucson

I like the multiple senders idea.... you could put them on a rotary switch. Another peeve of mine is that most of these older chevies with gauges do not also have warning lights and buzzer. This is easy enough to fix using an electric fan thermostat sender in one of the spare bung holes. I like these senders because you can get one that turns on as low as 200 degrees while there's still time to ponder your next move before the thing is cooked.

well I put a mech. temp gauge in the intake, next to the thermostast. s& left the elec. temp sending unit in the head.
as I have stated it it a bbc 454

at idle after 15min. 800 rmp.

electric in head reads ...225 and holds there
mech. in intake reads ... 155 after thermostat opens at 180, close until it gets to 180 again then drops back to 155

at 60mph after 15min warm up.

elec. reads 225 & holds
mech. reads 160 and never got to 180 until a stopped & idled for a min. then back down to 155

does this sound like a acceptable heat range for the motor?