I'm getting mixed signals on my engine temperature. I have a 1975 rebuilt 350 in my 69 Camaro. It was completely gone thru by a local machine shop, including vatted. It wasn't a heavy performance re-build. It's bored 30 over, small cam, Edelbrock Performer intake and 600 CFM, plus a set of headers. All other parts are stock, including the heads. I have two temperature sending units. The gauge unit is located at the back of the passenger side head and the idiot light unit is at the front of the driver's side head. The gauge shows 220+ and the idiot light is on. I read the temps with a Infrared Thermometer. It shows 220-240 on the heads but 180 at the thermostat and radiator. Also, when you open the hood, the bay doesn't feel unusually hot. Oh yes, there's not a used part on the car. Everything, including the 180 degree thermostat, water pump and radiator is new.

Does anyone have an idea? Has anyone measures the temps at various spots on their SBC engine? Since the sending units are tucked in between the header pipes, can this distort the temps?

 

Your heads tend to run hotter than the rest of the engine, and headers make it even worse by creating more of a heat soak situation into the heads. It's not because the sending unit is between the headers, as the probe is reading coolant temp inside the head. Because of that, I prefer to have my gauge sending unit in the intake manifold because (as you found out with the thermal) that's reading a more stable temp of the coolant flowing through the engine, not just at the heads. If you want to have two gauges, you could read both head and engine heat separately.

 

yea what he said

 

^^ lol

 

My sensor is on the side of the block and when I get much above 210, the engine starts coughing and spitting and missing... If it ever got up to 220, I don't think it would even run.

 

Thanks for the input, but are you saying that 220 to 240 is reasonable? I feel dumb asking this but is it possible to put the head gaskets on wrong causing some of the water ports to be blocked? I'm wondering if I'm not getting good flow thru the heads.

 

OK, I’m answering my own post for any future searches on this subject. First off, Camaro 69 was correct; heads just run hotter. Here's what I found so far:

1. When reading head temps with an infrared temp sensor, don’t point at the head between the headers. The sensor reads the air temp, not the head and the headers have a major impact on the air temp. The appropriate place is the front or back of the heads. When I did this, it was 180*. When I held it right next to the temp sending unit, it read about 20* cooler.

2. Make sure your timing is right. My timing was at 8* when it should have been between 12 and 16. This stabilized my temp gauge (reading at the heads) at 215*.

3. Make sure that the wire to your idiot light hasn’t melted to your header. (yes, the word idiot is appropriate in this case). When I corrected this, the idiot light did not come on.

4. I added a 1” riser under my carb and it eliminated the engine sluggishness after warm up.

Other things I will try if the engine continues to be sluggish after extreme warm up: Replace solid fuel line between pump and carb with braided line and use aluminum to shield fuel line, running along sub frame, from the passenger side header.

BTW, I'm in central Texas and it's been at or above 100 degrees so I would expect the engine to run hotter than normal.