erratic temperature

[Katherine Ilowiecki]

I have a crate engine from GM in my 59. The temp. guage is erratic and runs on the hot side, just below 220. 160oF thermostat is installed. the engine is a 270hp with a fan clutch. Original radiator. Any ideas on having it run cooler?
Thanks

[Joe L.]

Re: erratic temperature

Katherine------

If by "erratic" you mean that the gauge fluctuates more-or-less wildly at times, I would expect that represents a problem with the gauge or sending unit. A poor ground is a likely suspect. Make sure that no sealer or teflon tape was used when the sending unit was installed in the cylinder head or manifold.

I don't understand one thing you mentioned. You say that you have a GM crate engine installed and later say that the engine is a 270 hp. There is no 270 hp GM crate engine that I'm aware of but there was a 270 hp engine originally used in a 1959. So, I don't know what engine you actually have installed.

If your main concern is that the engine runs too hot and if you actually have a GM 350 cid crate engine installed, it might be that your original radiator is not capable of handling the heat rejection due to a variety of reasons.

[Joe R.]

Re: erratic temperature

Hi Katherine:

Three things come to mind:

1) As Joe Lucia has noted, if the temperature is fluctuating erratically, there is probably a problem with an electrical connection, the gauge, or the sender.

2) An original radiator is well beyond its expected useful life and may be partially clogged.

3) A common problem with C1 and C2 Corvettes is that the temperature gauge reads incorrectly. If the sender has been replaced, the resistance range of the replacement sender often does not match the original sender, leading to incorrect (usually high) readings. Try using an independent method to measure engine temperature, such as an infrared temperature gun.

[Katherine Ilowiecki]

Re: erratic temperature

By fluctuate I meant that the temp guage does not maintain a stable temp. On the highway it tends to run hot, 190 to 210 depending onthe air temp. and speed. It then goes down on local backroads if i'm in the shade, at traffic lights it goes up again. Idling, the temp goes up.
The original radiator has a new core and with the original engine ran cool.
I havn't actually seen the paperwork on the crate engine so I am sure your assumption of 350cid is correct. The radiator issue seems to make a lot of sense to me.
Thanks,
Katherine

[Joe L.]

Re: erratic temperature

Katherine-----

The fluctuation that you describe sounds pretty normal to me. The temperatures that you describe for various operating conditions might be a little high, but not all that much out of range. The reason that they may be a little high is the additional heat rejection from the larger engine.

Also, keep in mind that the thermostat only controls the LOWEST temperature that an engine will operate at. It has nothing to do with the MAXIMUM temperature the engine will operate at. Once the coolant temperature gets to the thermostat's rated value, the thermostat is fully open. Other factors come into play with respect to how hot the coolant temperature gets. During open road driving on a flat road with cool ambient temperatures you should see about the lowest temperature you're going to see. That would represent about the lowest temperature that your cooling system is capable of maintaining. VERY likely, it's going to be higher than the thermostat's rated temperature.

[Jack H.]

Re: erratic temperature

I echo what Joe says! Plus, keep in mind the factory original temperature reporting system was NEVER that accurate from the git go.

It was designed to replace the 'idiot' light system most of the base passenger cars had. If you look at the original GM drawing for the temp sender, there's a graph showing acceptable vs. unacceptable temp vs. resistance readings. The band for acceptable performance is pretty wide/sloppy at lower temps and doesn't narrow for high precision until you're in the bona fide overheat range (240F and above).

Combine that with a history of the part being re-released + copied by aftermarket parts suppliers (they LOVE to make 'one fits all' stuff to reduce inventory proliferation) and we pretty much accept today a native accuracy range of approximately 15F under 'normal' driving conditions where the gauge is running in its mid-range.

A lot of folks 'panic' when they see these kinds of temperature reporting inaccuracies because (A) they're used to today's cars that're pretty darn precise and accurate, and (B) they've got a new engine in 'baby' and they're VERY concerned something might be wrong and/or sub-optimal.

But, there's a reason why the standard temp guage lacks gradicules across its face (those are the tick marks used to call out various temperatures) and it's because the system wasn't all that 'hot' to start with. The time to really worry is when you see a guage that's pegging or has risen well into the RED zone. That's the time to SHUT down IMMEDIATELY and go look for problem(s).

All of the above is why some are suggesting you get an 'independent' opinion on the accuracy of the temp reporting system by using an IR thermometer to double check the actual temperature of coolant in the system vs. what the gauge on the dash says...

[Verle R.]

Re: erratic temperature

Katherine,

What is on the engine for carburation?
What distributor are you using?

The way the distributor is set up and total timing can cause high temperature.
A lean carburetor will cause it to run hot.

Start with the distributor and timing.

Verle

[Katherine Ilowiecki]

Re: erratic temperature

Verle,

One single four barrel carburator.
New distributor but I have no idea "what" one it is. No points. Electronic ignition.

Any agreement on the old radiator not having the capacity to deal with a bigger engine? It was recored and had no problem with the original engine and you know that it was put through some rigorous conditions.