If the temp creeps up during cruising, shouldn't you check your front spoiler? I never have problems with heat at speed, and mine is bone stock (except for the duals). If the front spoiler is damaged or gone, there will not be enough air flow thru the radiator. Something to check anyway...

I put a new spoiler on when I restored it. I'm going to take a look at the seals around the radiator. Thanks for the suggestion though. Tom

Hi Tom
Ihave a stock 78 L-82 { run a 160 thermostat and the gauge never goes over 180
If the radator is sound
check the ignition timing.If the timing is late the
motor will heat up,no performance, and poor gas mileage!
The thrrmostat only determines minium engine temp.
Steve

TomB, no problem, let me know what you need. It is in the shop right and has been for the past week, but if the guy still has not done anything to it by tomorrow night, I will go get it.

First thing is to make sure the gauge is accurate. Go to a radiator shop and have them shoot various points on the motor and radiator with an IR gun. If the IR gun confirms the high temps and you have already looked into the obvious thing (thermostat, radiator clean, etc...) try removing the two half inch hex head bolts located on either side of the block just above the oil pan. The bottom end of the motor may be clogged with rust. If clear, the remainder of the coolant should run out these holes. Sometimes it requires a coat hanger to root around in there an help pull the sludge and rust out. Good luck.

I've had this exact same problem on my 1969 with a modified 350/300 base engine. It has an Eblebrock Performer cam and intake manifold and headers. I had replaced the temperature sender with a $9.00 unit from Zip thinking that this was better than the $4.00 units at the local parts stores.

The temp guage consistently showed "normal" operating temperature at the hash mark between the 200 and 225 (red line) marks on the guage. I had the radiator re-cored and the cooling system flushed. Still no change, so I used a couple of hose clamps to attach a long stem AC thermometer to the upper radiator hose right at the thermostat housing. Conparing the thermometer reading (after a long drive) to the guage, the guage was reading 32 degrees high!

Another way to check it is to look at your temp guage as the engine warms up. I have a 180 degree thermostat. Watch the needle as it rises. When the thermostat opens, the needle (temp) should drop as the cold water enters the engine block. When I did this, my needle dropped exactly at the same hash mark meaning that what reads as approximately 215 degrees on my guage is really 180 degrees.

I've read in more than one article that a Wells TU5 temp sender (get it at AutoZone) is recommended as a very close replacement to the original. I'm going to try this next.

Hope you fix your problem,
Jim