Topic: 68 J code cooling issues

[68NordicCat]

12/67 SJ built 68 Cougar J code 4 speed - rebuilt engine, new water pump, all new hoses, 180 degree t-stat, original 7 blade fan and original fan clutch, original restored radiator, running Evans waterless coolant. When breaking in the motor and driving 1st 75 miles or so (city) the temp gauge would creep up to the top end of the range. Downhill on a cooler day it would back off some but pretty much stayed pinned, especially at idle and when parked. Shot the top of the engine with a laser thermometer and showed 230+ degrees. Seemed like the fan wasn't spinning right so I replaced the clutch (current replacement to see if that was the problem before spending $$$ on an OEM or rebuild). After driving for 30 min or so in city on a hot day the temp gauge stayed in what I would call a normal range - just below or at midway point, maybe a little higher while stopped at idle but would then back down. Thought the problem was resolved but when shooting the top of the motor with the laser thermometer was getting 230-240 degree reading still. I tried shooting several spots on the manifold including at the water temp sender. I'm confused .

- Should I be concerned with the hi temp readings from the thermometer or trust the gauge?
- Am I right on the correct indication on the gauge? From other threads it seems like that is right.
- What temp should I see at the top of the motor if everything is working correctly?
- Should I shoot temps at some other location on the engine to get a better read on running temp?
- Anything else I'm missing or should be looking at?

Have tried searching threads and haven't come across the answers but if I'm missing something feel free to just point me that way. Thanks for all the great info here and any help on this.

Dan

[midlife]

Top of the engine is not a good place to test water temperature.  The better location is the upper hose between the radiator and the engine, as that represents the outflow of the engine water.  If you want to put your thermal gauge onto something metallic, the thermostat housing would be recommended.

[dave6768]

Water temperature is what you need.

Don't trust the gauge....trust but verify.  It does not have any temperature values on it.  It only provides a relative indication.

If you want to take a deeper dive, you can do a calibration curve on your temperature sensor relative to your temp gauge.  I can share how I've done it.

[68NordicCat]

I've taken a reading at the t-stat housing - again around 230 degrees. At the upper hose it is more like 210. Really less concerned about the gauge than about getting the temp of the engine right. What should I be reading for temp? From other threads it seems like 190-200?

[krelboyne]

Do you have a fan shroud?
If it is a 20 inch radiator, do you have the 2 vertical block off plates installed on the sides?

[Coralsnake]

Do you a spring inside the lower rad hose?

[kcodecoupe]

Check to see if both head gaskets were installed correctly, you should see a square shaped part of the head gaskets sticking out inbetween the block and head surface on the L/F and R/F heads, if one is installed backwards the flow of coolant will be blocked,

[Juanball Mustang]

Check your timings not retarded and carby mixture not running lean.

[68NordicCat]

It's a 24" radiator with a shroud. Have concours reproduction hoses (think they are from Marti) so I assume there is a spring in the lower hose but I will have to confirm that. It appears both head gaskets were installed correctly. I think timing and mixture are good. Still looking for info on a good location to shoot the laser thermometer and an idea of what temp to look for. Thanks for all the great input so far.

Dan

[midlife]

Best location for IR sensor is to aim it at the thermostat housing, as that gives the best indication of water temperature that the thermostat sees.  From there, one can look at both incoming and outgoing portions of the radiator to see how effective it is cooling the water.