'65 running hot

[Jeremy Hedges]

My '65 L-79 is running to hot (220+ in just a few miles) Just been rebuilt, has 300 miles since frame off resto. I have put the breakerless ignition in it but other than that it is a stockk L-79. The timing has been set and is correct. Flushed coolant and still have problem. Thermostat is Ok, I have even taken it out. Radiator is a brand new Griffin Aluminum radiator. Clutch fan works properly and water pump is stock. Engine is bored 60 over. Could that be the problem? How can I get it to run cooler? Any help?

Jeremy Hedges
#31711

[Don H.]

Re: '65 running hot

Are you sure it is really that hot or is that what the temp guage reads? I would get something to verify the true temp (the new "gun" type tool is not real expensive). Does the rediator (overflow tank) boil? I would expect a .060 over engine to run a little hotter than standard bore but not the temps you descibe. Don H.

[John H.]

Re: '65 running hot

Jeremy -

Put the (180*) thermostat back in - it's a calibrated orifice that modulates flow. Is your vacuum advance working properly and connected to full manifold vacuum? Correct fan shroud in place? Radiator sealed to the rad support?

Have you compared an I.R. gun "shot" of the thermostat housing to the gauge reading so you know what it's telling you?

[Rob M.]

Re: '65 running hot

Jeremy,

Don and John are right. I had the same problem and put an I.R. gun on it and learned that the gauge reads @15 degrees above actual. I would put the 180 back in it and check the temp with an I.R. gun. Sure made me feel better.

Rob

[Les Jacobs]

My gauge was 30 degrees over actual. *NM*

[Jeremy Hedges]

Fixed!

Thanks for the respones. it was the sending unit. I had heard before that some of these were inaccurate, so I got one that was correct, or so I thought. This one was brand new and said to be calibrated, bought from Corvette Central. I took the one out of my other '65 and it works great, now running 180.

Thanks

Jeremy
#31711

[Randy S.]

Re: Fixed!

Jeremy,
I have the opposite problem, my gauge reads 40* low (140 gauge 180 actual). I am pretty sure it is the gauge. I would be interested in buying your corvette central sender as I believe 2 wrongs may make a right.

Randy

[Dick W.]

Re: Fixed!

Randy, old trick to check guage. Not 100% accurate, but close. Remove wire from sending unit. With ignition switch on, ground sending unit wire. Guage should read full scale. This will give you a fairly accurate indication if it is actually the guage, or in fact, as in most times, the sending unit.

[Randy S.]

Re: Fixed!

Dick,

In a previous post about 3 months ago I had asked about temp gage and someone responded with three resistor values that give low medium and high gage readings. My gauge was about 40 deg low on all three resistors, thats why I think it is the gauge. I have replaced the sender with same result; 140 indicated, 180 actual.

Randy

[Dick W.]

Re: Fixed!

Missed that post. Probably more accurate than the SWAG method that I was talking about.