Temperature gauge and Headers

[Kiqman]

I put headers and electric fans on the Blazer. On the new heads the temperature sending unit for the dash gauge sits right in between two of the head pipes. My temp is running at about 240 degrees according to the dash gauge. Is it possible that I'm getting a higher than actual reading due to the sending unit being positioned between the two scorching hot exhaust pipes? I replaced the thermostat thinking that it was stuck shut. New thermo and my dash temp gauge still has me running at about 240. I'm having no signs of overheating other than the dash gauge. It never gets on the red but damn close. I'm afraid I'm frying my new rebuilt motor. Half the time I'm driving with my electric fans manually turned on and the heater blasting to keep the temp gauge at 210 - and it's winter!

 

[goldwing2000]

External heat shouldn't affect the sensor but that much heat exposure can shorten the life of the sensor and wiring. First thing I would check is to make sure the gauge is accurate.

After that, move the temp sensor to the water outlet or intake manifold crossover.

 

[Kiqman]

How do I check the accuracy of the temp gauge?
The temp sensor screws into the head. How do I relocate it without drilling a hole? What do I put in the hole it used to fill?

 

[ryoken]

you shouldn't be having an issue with the location.. the sensor is IN the head touching the coolant... btw, a NPT pipe plug is what you would use to plug a hole like that...

what kinda gauge? i'm betting either you have the wrong sender for the gauge, bad gauge or your actually running 240...

infrared temp guns are invaluable in cases like this for reading any kind of surface temp... can be had for under $75

 

[destinbeachman]

Check the sender by putting it in a pan of water and boiling it-you'll need a torch or something to heat up the pan while it's sitting under your hood.you may need to keep the unit grounded,but I'm not sure.Check your gauge as it begins to boil and it should read just about 210.If you want to move it it can be accomplished by drilling and tapping your water neck or intake manifold and you fill the original hole in your cylinder head with a pipe plug from Ace.

 

[goldwing2000]

How do I check the accuracy of the temp gauge?

Put it in a pot of water and heat it. When the water boils, the gauge should read around 212°.

The temp sensor screws into the head. How do I relocate it without drilling a hole?

There should be a hole somewhere around the water outlet. If there isn't, then you can get a new water outlet that does have a hole. Or you could drill and tap a hole into the intake manifold.

What do I put in the hole it used to fill?

Brass pipe plug. Should be a standard size.

edit: d'oh! two minutes too slow!

 

[destinbeachman]

Yup,great minds think alike.But I really don't think the location is his prob.

 

[dyeager535]

Just as an FYI, this is where mine sits (I think you can see pics linked like this) and it's dead on with the ECM temp sensor readings:

 

[goldwing2000]

Yup,great minds think alike.But I really don't think the location is his prob.

I agree but it couldn't hurt to move it away from the heat. Some sending units can be finicky.

dyeager535: that's where I've always had my sending units, too.

 

[R72K5]

and ill just add that ever since 1968 the driver side cylinder head is where the temp sensor has been on the sbc engines anyways

67 and older they were in the intake by the thermostat housing

you sure that those electric fans are putting good air through the radiator ??

waterpump is pumping good?

good pressure builds up in the cooling system ?

need all three to stay cool

240 is a bit warm to me, i wouldnt like it at all



good luck

 

[13lazer]

just an idea, i did this when i was 17. is your thermostat installed upside down? if so it wont open.

 

[Kiqman]

The thermostat is installed right side up. I made that mistake in the past too. The water pump and radiator were both replaced during the rebuild. I believe there's pressure in the system because I feel it when I pinch the top hose. I know the thermostat isn't sticking because I've had two in there and they both acted exactly the same. The fans I have on there are dual sucking Flex-a-lite 10". I wonder if I could just wrap some heat tape around the sending unit. Perhaps my cheap Flowteck headers just put off too much heat. Other than on the dash gauge the truck doesn't seem like it's at 240 degrees.
Oh and thanks for all the good posts guys.

 

[Smitty]

The thermostat is installed right side up. I made that mistake in the past too. The water pump and radiator were both replaced during the rebuild. I believe there's pressure in the system because I feel it when I pinch the top hose. I know the thermostat isn't sticking because I've had two in there and they both acted exactly the same. The fans I have on there are dual sucking Flex-a-lite 10". I wonder if I could just wrap some heat tape around the sending unit. Perhaps my cheap Flowteck headers just put off too much heat. Other than on the dash gauge the truck doesn't seem like it's at 240 degrees.
Oh and thanks for all the good posts guys.

I doubt the headers are affecting the readings at the sending unit. I've run a lot of small blocks with headers and haven't had a problem with that sending unit location. I'd try the heat gun or even a mechanical gauge to check the actual temperature. You might have a problem with your wiring, gauge or sending unit. A mechanical gauge would narrow it down to one of these three items unless your engine is actually running at 240 degrees.

 

[Chevy305]

http://www.jegs.com/webapp/wcs/stores/servlet/CategoryDisplay?lang=-1&catalogId=10002&storeId=10001&categoryId=13443&searchItemId=13401

This is the thermostat housing I have and I have a mechanical sending unit threaded into it. I also have a 160* thermostat and flex fan. So on cold mornings my temp hardly gets above 115*. I know its a little low since the gause is off a little, and I realize that you have fuel injection so changing the temp of of your thermostat is out of the question.

Just food for thought. Put a mechanical gauge into your thermostat housing and you'll get a better reading.

Also did you personally rebuild the engine or did a machine shop do it? Sometimes machine shops can be sloppy and drop something into a water passage and block it off.

 

[Kiqman]

I had a machine/engine shop longblock the motor for me. God I hope they didn't leave something in one of the cooling chambers. It will run at 210 all day on the freeway. These news heads just don't seem to like to lope around town.