I have a 1969 351W 2bbl Cougar. The engine was rebuilt and bored 0.30 over. The car has started experiences overheating problems when stopping after driving. I have replaced the radiator to a 3 row aluminum stock looking radiator from WCCC. The head gaskets were just replaced. The water pump, fan clutch, thermostat (180F), water valve for the heater have also all been replaced. The car fires up nicely and the temp gauge reads at 5/8 when the thermostat opens. I had the engine taken back to the machine shop that rebuilt it and he couldn’t find a problem with it. I then took the car back to the transmission shop and they couldn’t find a problem either. I was told that the inside portion of the torque converter in the car (I have an FMX) is always engaged even when stopped at a red light. In 1978 or so they invented a locking plate that disengages at red lights so that the inner part is not engaged anymore. When driving the car runs beautifully. The temp creeps up at stop lights in drive and that is what makes me nervous. The trans fluid is still bright red and there is air flow when the car is stopped. In park the car can idle for a while and nothing will happen, but in drive and after driving at speeds of around 55 for 30 minutes the temp slowly creeps up. There aren’t any leaks in the system and at this point I’m at a loss. Any ideas would truly be helpful.
The upper radiator hose is 198.6 and the lower is 170.4.
Both issues tend to point to a water pump problem. “The temp creeps up at stop lights in drive” “after driving at speeds of around 55 for 30 minutes the temp slowly creeps up”
Temp. at 199 at exit of upper hose does not seem to me as overheating…
See what mine does after stop and go in heavy traffic (early 1970 = same engine as you) and it drives really well: https://cccforum.discoursehosting.net/t/running-hot-or-reading-gauge-wrong/7827/13
Your gauge being at 5/8 when your Tstat opens seems too high to me, mine is at about 1/3 when Tstat opens.
You most probably know, but temp of the rubber hose can not be measured accurately with a laser thermometer, you need to point at the metal on top of the radiator right next to the exit point (see pic in above link).
If you have a clutch fan, make sure the clutch is still engaging. You need that airflow over the radiator when stopped. If you don’t have a fan shroud, that might help as well.
The fan and shroud were my first thoughts as well, though I’m curious what other changes happened around the time the overheating started, if nothing else I might suspect the sending unit going bad.
Here’s a thread on sending units that might be worth a read :
20 degree difference between the upper and lower radiator hose sounds like the radiator is shot, or the fan has no fan shroud, or the timing is way off. I would start by making sure that you have a fan shroud, then check the timing with a dial back timing light to see what’s really happening.
I do have a fan shroud and the radiator is brand new. I tested the sending unit with a multi meter when the engine was cold (air temp was 55-60F) with the multimeter set to 2,000 ohms. The reading when cold was .357 which was 357 ohms. Is that a normal reading for a cold engine? The fan clutch engages and disengages when it should and its also brand new. I did notice that if I put the car in park after its been run a little while and step on the gas to increase the rpm to about 1,200 the gauge drops a little.
That is because more air is pulled through the rad at higher rpm. To optimise the amount of air that is pulled through the rad at any given (lower) rpm, the fan shall sit 1/3 in the shroud and 2/3 ahead of it toward the engine. If the fan sits too deep in the shroud, efficiency of the shroud is tremendously reduced.
Check your waterpump pulley ratio, on the street a waterpump should turn 10-15 % faster than the crank pulley. Racing is 1 to 1. You might have to go to a smaller pulley on the waterpump to spin it faster.
Heat transfer is a function of two things: moving the water through the system and moving air through the radiator. If you are going down the road at 60 and it is slowly getting hot, it is not a air problem. The ram air effect of going through the grill at 5280 CFM per square foot of area is more than enough. Speed requires horsepower and horsepower equals heat. although you have a new radiator, you have to verify coolant flow. Look at the size of the radiator hoses. Compare that to a garden hose, and you start to get an idea of how much water flows through the system. If you can take off the bottom hose, and run a garden hose from your house into the top, running full blast, and it over flows the top of the radiator, then you have a radiator problem. If it looks like it can handle that and more then the radiator is probably okay. The next thing to look at is the water pump and thermostat. Some replacement thermostats are too small for a V8. Use the Mr. Gasket or FlowKooler design for better results.
I took pictures of the radiator and the fan shroud as well as measurement of the fan shroud. The fan shroud is a 24 inch fan shroud. But the fan is definitely more the 1/3 into the shroud. The fan is a 7 blade small block with AC fan and I posted a picture of the part number on the blade. The water pump is stock, the radiator is aluminum, but a stock replacement that just so happens to be aluminum. I know the fan placement is fixed and the radiator is in the stock support. The fan shroud is plastic so it is not original. I looked on WCCC website and saw there was a big block radiator shroud and a small black 24 inch radiator shroud. How would I tell the difference or possibly adjust the fan so it is 1/3 in and 2/3 out?
What year engine is this? Could this be a late model reverse rotation water pump? It looks like the radiator is pushed back towards the engine by several inches. The top mount looks funny.
As Bill says, it is either poor coolant flow in the system of poor air flow through rad.
I would think that if you can drive for extended periods at 30-60 mph with needle stable at ± ½ non stop and that it starts to climb only when you stop and wait (in drive) at red lights/traffic, then I would suspect lack of air flow, especially if it does not climb as much if you put it in park while waiting at red lights (you gain ± 100 rpm in park).
If it climbs while you move, then I would suspect poor coolant flow, especially if it climbs higher when you move faster since faster requires more combustion = more heat.
Here are pics of my set up (351W 2V but no A/C hence with smaller 20" rad). 6 blades fan directly attached to the water pump pulley, no spacer no fan clutch.
As far as I know, the normal operating temperature for that engine is ± 205°F, so if yours stays at 200 I do not think it overheats and may this is only your gauge that is little off.
Edit: changed pic.
