I started my new motor tonight and after a minute or two of running the temperature was at like 260*! I had to get a new coolant sensor for the head because the sensor from my old head was too small for the hole. Could this sensor be the wrong voltage for my stock gauge or something? It doesnt seem like the engine was that hot. The radiator cap was off and the water was not boiling over or anything. Any help or advice would be appreciated! My car is running fine and I set the timing to 8*btdc but the temperature scares me!

Sounds like it might be giving the wrong OHM value to the gauge. If the radiator was not overflowing and you could see the coolant moving I doubt it was hot. are you running without a fan shroud?

no I have the fan shroud on there as well as an electric fan. My temp would never get above like 180 or so on my old motor, but that was with the old coolant sensor. So how do I know what resistance I need and where do I find the right sensor?

I had a similar problem on a 383 85 impala I built for my cousin (don't ask). The car ran really hot on breakin. Shut it off got mad and went in the house too cool down (both the car and me)and to think it over. Came out add some coolent never had a problem again. I guess it had air in the block and had to burp, then once full no more problem. You may have a similar problem if it is a NEW motor. Just an idea.

The radiator cap was off and the water was not boiling over or anything.

Here on the left coast water at atmospheric pressure boils at 212°F. If I was faced with the dilemma of trusting a half-vast temperature gauge or the laws of physics, I'd have to come down on the side of physics.
Get yourself a direct reading temperature monitor and calibrate it in a pan of boiling water. Install it on your engine.

I would replace the sending unit for starters, then look at your thermostat to make sure it is not sticking.

I read somewhere on here that teflon tape will impede the flow of electricity and that the temp sender is supposed to ground to the head. I took the temp sender out and took the teflon tape off, and i also noticed my water pump is cracked because the fitting for the heater hose was screwed in too tightly(oops how did that happen? lol). Not much water is leaking out though. Would that affect anything? Im going to change the water pump and take my thermostart out and boil it to make sure it opens, then try again.

Buy a $10 mechanical temp guage. The one that has the copper capilary tube on it, not the one with wires. Put that in the hole and use that. MUCH more accurate than an electric one.

260* after just a few minutes of running? Where are you, the Sahara? I wish my car would warm up that fast! I don't see an engine going from a cold start to 260* in just a few minutes.
Maybe your timing is retarded? I know you sait it's 8* advanced, maybe the timing pointer is in the wrong place?
If the timing is correct, I'd suspect the gauge or a stuck thermostat, but even with a bad stat, I don't see it warming up quite that fast unless you have air in the system.

<font face="Arial,Verdana" size="2">Originally posted by Air_Adam:
Buy a $10 mechanical temp guage. The one that has the copper capilary tube on it, not the one with wires. Put that in the hole and use that. MUCH more accurate than an electric one.</font>

Not according to AutoMeter

http://hp.autometer.com/techtips/faq_tech_writeups/mechvselectric/mechvselec.html

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70 Camaro Z/28 with 461cu.in. BBC & OD Auto, 3.31 12 bolt posi.

there very well could be air in the system whats the best way to purge the air out?

1) Yes, there are different sending units for factory gauges- one for gauges up to 1978, another for 79/80 and another one for 1981.

2) Yes, air pockets may be helping to make temperature appear higher. To purge the air- fill the rad and the coolant recovery bottle- run/drive the car long enough to get the thermostat to open (you'll know its opened because coolant level in rad will change)- top up the coolant, intall rad cap and run for awhile longer. Then park the car at a slight front incline and let it sit overnight to cool off and let the system expel air and draw coolant from the recovery bottle. Top up recovery bottle before running engine again.

<font face="Arial,Verdana" size="2">Originally posted by white 81:
there very well could be air in the system whats the best way to purge the air out?</font>

I've heard of a trick some guys on here have used, which is to drill a couple small holes in the thermostat about 1/8 inch dia. this will let the air escape by the thermostat when its closed.

eric the temp sender i have is from a 75 camaro because the heads I have on there have a larger port than my old heads. Does it send a different resistance to the gauge depending on the year?

yes, i believe a few guys experimented with all three versions of senders... the send er needs to match the year of the gauge... i had this same issue when i used a newer gauge and a 71 sender..
i have a second temp gauge (mechanical) plugged into the pass side head, and that tells me i never run over 190*..

Yes to what RS_SS said- gauge must match sending unit. As theflash mentioned- drilling holes in the t-stat will help- but will not eliminate all possibility of air pockets- only proper coolant circulation and a closed radiator cap with fluid in the recovery bottle will accomplish this over time.

Another method to burp air out of the cooling system is to:
Remove cap on rad and top off
Leave cap off, and start engine
Let engine run until operating temp or T-stat temp is reached, at that time you will see the coolant down the rad cap hole moving more vigorusly
Let it run like this for awhile, air will be burped out along with some coolant, when it settles down, shut engine off, let cool, top off coolant leaving a bit of room for thermal expansion, replace cap and your good to go.
Holes in the T-stat are a good idea, they HELP any trapped air to burp, but is not 100% effective. Holes in the T-stat provide additional bypass or flow until the T-stat opens, this is required with hi-flow water pumps. The method of removing air from the cooling system I quoted, is from the Stewart water pump site.



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70 Camaro Z/28 with 461cu.in. BBC & OD Auto, 3.31 12 bolt posi.

Well the engine really wasnt getting that hot, it was exactly what I though it was...the sender did not match the gauge. I bought a 3/8 to 1/2 inch adapter pipe fitting and used my old sender. It barely got up to 180 tonight! Man it feels good to drive my car again!!

<font face="Arial,Verdana" size="2">Originally posted by wayner:
Not according to AutoMeter

http://hp.autometer.com/techtips/faq_tech_writeups/mechvselectric/mechvselec.html

</font>


Sorry, guess I should have been a little less vague...

I meant to say that a mechanical guage will be more accurate than a factory electric guage. (ie. what came with your Camaro)