Normal Operating Temp?

[TJ's GMC]

Hi guys, what's the normal operating temp for a 67 305E? The 60-61 shop manual states 160 degrees for a 305A. Did that change? Been having funny readings from my gauge. As you all know I did a light rebuild on the engine and during that I installed a new Temp sending unit from Napa. Ever since then the temps seem to act funny on the gauge. Normally the engine runs just below Normal. And when it Did run at Normal I was towing 10,000 pounds and sometimes it would go just a tad past. When you'd pop the hood you could feel the motor was Hot...maybe around 190 degrees. This was before the rebuild....now after..and with the new sending unit...it stays around 1/4 to just below norm most of the time...but if I let the truck sit for let's say 1 hour...and go to drive...while driving the gauge goes to norm...and just slowly keeps climbing....until it reaches the 3/4 mark. And this happened today, warmed up the truck for about 5 minutes at a 800 rpm idle. Bank is about 3 miles away...made it there and motor was at 1/4 temp. Truck sat for about 10 minutes. Fire it up and heading back home I'm watching the gauge just keep climbing...especially under acceleration. Speed on home, pop the hood and to my surprise....the motor isn't even that Hot! I could still easily hold onto the top rad hose without getting burned. Could almost hold onto the thermostat housing to. So I have ruled out that the motor isn't actually Over heating. Maybe it's the thermostat? Faulty new sending unit? Dunno guys, what do you think? What was the rating for the stock t-stat?

[bobdylan]

What temp. thermostat are you running?

[TJ's GMC]

Originally Posted by bobdylan

What temp. thermostat are you running?

Same one that was in there when I got the truck, so I assume the stock one.

[Funky61]

TJ, maybe a loose ground on the back of the gauge cluster(?) I added an external one with numbers.

[James]

Did you used Teflon tape? If you did it could interfere with the grounding of the sending unit. You should not use Teflon tape on the sending unit, use a very light coat of gasket sealer on the thread. If you have an ohm meter you could measure the resistance from the brass base of the sending unit to the battery negative terminal, with the ignition key off. It should not be more than a couple of ohms. If that check good I would suspect a bad sending unit. If more than a couple of ohms then the ground connection between the water manifold and the head could be at fault, I'm assuming you had the head off. If you do not have a meter I would put the old sending unit in and drive it to see what is happening. You should be able to switch them with minimum lose of coolant.

[TJ's GMC]

Originally Posted by James

Did you used Teflon tape? If you did it could interfere with the grounding of the sending unit. You should not use Teflon tape on the sending unit, use a very light coat of gasket sealer on the thread. If you have an ohm meter you could measure the resistance from the brass base of the sending unit to the battery negative terminal, with the ignition key off. It should not be more than a couple of ohms. If that check good I would suspect a bad sending unit. If more than a couple of ohms then the ground connection between the water manifold and the head could be at fault, I'm assuming you had the head off. If you do not have a meter I would put the old sending unit in and drive it to see what is happening. You should be able to switch them with minimum lose of coolant.

No teflon tape or any sealer for that matter. haha Could be a ground issue because it only does it certain times. There will be times I will go 20 miles cruises and it never gets past normal. But if I drive to work and back...let the truck sit for an hour...then drive somewhere the gauge just keeps creeping. lol Must be coincidence.