Why is lower rad hose a higher temp?

[mosel70]

'70 C10, 402. I have all new cooling system components to include Summit's water pump SUM-312461
Water Pump, Mechanical, High-Volume, Iron, Natural, Chevy, Big Block, Long, Each

I've noticed my upper rad hose from T-stat to upper/drivers side rad is 10-20 degrees cooler than the lower/pass side hose to water pump.

Q. Does that mean coolant is flowing OUT of the water pump to the rad and is the more accurate temp?

[MagmaJct]

Interesting.

Where does your heater flow to?

Apparently, at least on the SBC, for manual transmissions the heater core returned to the pump. On automatics, the heater core returned to the cool end of the radiator.

I suppose if the thermostat was regulating the coolant around 185F, which is a common aftermarket temperature, and the heater was returning hotter coolant to the radiator, then that might explain your inverted readings.

Of course, if your fans are off, this would make a lot of sense, as there'd be very little cooling taking place.

[Wrenchbender Ret]

That is weird. I wonder if you got a water pump for a Serpentine belt. It turns in the opposite direction.

[Alex V.]

Hmm! From doing a lot of work on front-wheel drive cars that requires letting the engine sit and warm up, I can say the cooling capacity of the radiator even without fans running is enough to maintain coolant temp for as much as 10 minutes before a fan needs to kick in for the first time. That is to say, even with an elec. fan setup I can't imagine the lower hose would be the same or higher temp. than the upper if the system is full and it's flowing the right way, regardless of heater hose routing.

[MagmaJct]

Originally Posted by Alex V.

Hmm! From doing a lot of work on front-wheel drive cars that requires letting the engine sit and warm up, I can say the cooling capacity of the radiator even without fans running is enough to maintain coolant temp for as much as 10 minutes before a fan needs to kick in for the first time. That is to say, even with an elec. fan setup I can't imagine the lower hose would be the same or higher temp. than the upper if the system is full and it's flowing the right way, regardless of heater hose routing.

Perhaps. But consider the thermostat is probably regulating the coolant leaving the the engine around 185F. But if the heater core is dumping into the cold end of the radiator, it could potentially be increasing the temperature of the coolant entering the pump.

The original poster could also take a temperature reading of his heater hoses to confirm my hypothesis.

[57taskforce]

Originally Posted by Wrenchbender Ret

That is weird. I wonder if you got a water pump for a Serpentine belt. It turns in the opposite direction.

Exactly what I was gonna say. Make sure you don't have a reverse rotation pump.

[hjewell2]

I have a 1980 Malibu SBC and it does the same thing. when I put the thermal gun on the T-stat housing it says 212* with a 180 T stat. the hose says 185*
Lower hose 198* radiator 177* just before going to bottom outlet. top of rad by inlet reads 189* soooo I thought about this for a little bit. the gun is picking up heat from the engine block, the fan is blowing air right back at the block and going around it causing the readings what they are, feel free to chime in and correct me. as for my 70 C10 never checked it never gave me reason to, stays at 170* all day. now the Malibu is giving me fits with over temping that's why I checked it.

[hjewell2]

Originally Posted by firedemon

with those meters you need to be exactly the same distance from what your measuring or it will pick up temps from other sources especially the further you are away from what your measuring

yup what I figured

[davepl]

Mine has 2 lasers that intersect so you know you're at the "right" depth when they overlap and appear as a single dot. Handy.

Assuming your measurements are right, gotta be a reverse rotation water pump! Wild if true, never seen one run.

[57taskforce]

Originally Posted by davepl

Mine has 2 lasers that intersect so you know you're at the "right" depth when they overlap and appear as a single dot. Handy.

Assuming your measurements are right, gotta be a reverse rotation water pump! Wild if true, never seen one run.

Only reason I thought of it was I had a cpi 4.3 in an s10 blazer that AutoZone gave me a standard instead of the correct reverse pump. I had a similar issue with the exception that it ran 15-20* hotter than before I replaced the pump.

[mosel70]

Hey, I appreciate all the replies. Helpful. Thanks!

I have a 3-core Mishimoto rad and dual electric fans. I'm chasing an overheat problem where temps only increase at idle, not while driving. It eventually goes into the red and starts idling rough.

I had my temp gun the same distance away from both top and bottom hoses, even shot the temp from below the truck at same distance. Bottom hose always hotter than top hose. In the pics below, the hose from the pump goes to the hose on top on the firewall. Hose below it on firewall goes to intake manifold. I readjusted idle mixture screws on Edelbrock 750 carb to ensure it's not too lean, still overheating. I'm perplexed. Last two remaining theories is total timing is too retarded or the TH400 torque converter is overheating. The trans cooling lines go to the radiator. Engine overheats whether or not the A/C is running. The gauge in middle red is 216 degrees on top hose and 226 degrees on bottom hose and that's where it starts idling rough. Once I start driving at highways speeds it stays in the red or barely comes out of the red.
I removed the 180 degree T-stat and no changes noted, same issues.
I'll take temps of heater hoses this week and will post.
Oh, yeah, the pump direction. My understanding is that V-belt pumps are clockwise (which I have) and serpentine belts are for counterclockwise pumps. So I'm assuming (correctly?) that clockwise causes the pump to pull coolant in from bottom rad hose. But should mean cooler rather than hotter coolant which it's not.

[mosel70]

According to Vintage Air diagram, I have the heater hoses correctly connected.

[67 chevelle]

Originally Posted by Wrenchbender Ret

That is weird. I wonder if you got a water pump for a Serpentine belt. It turns in the opposite direction.

could be , and that would solve your overheating mystery

[67ChevyRedneck]

Do you have a better pic of your shroud? I had a similar problem with my mustang. I've found that "flat" style shroud actually blocks air from flowing through the radiator at highway speeds.

Almost all stock fan shrouds are 2-3" away from the radiator and are dished to let the air flow through. With those flat aluminum shrouds they're only 1/2" - 1" away from the radiator and being flat, they act as a wall creating hot spots inside the radiator because the air can't flow through.

[weq92f]

Hadn't thought of that ( the nice looking stainless steel "shroud" blocking regular at-speed air flow and causing problems ).

The argument seems to stand in my thinking anyway. So, the solution then would be...?

...Anything that allows free air flow is also going to diminish the CFM the fan(s) is/are capable of pulling through the radiator. It's a pressure thing. Allowing free flow is going to not allow as much negative pressure under the shroud during slow speed fan operations.

What gives? What is a nice compromise here between functionality and good looks?

Would a flapper over a vent hole on the "inside" of the engine bay/radiator shroud do the trick? That is, allow pressure when pulling from the shroud side, but also allow free flow through at speed?



-klb

[cleszkie]

My dual electric fan shroud covers the entire radiator core. But it does have multiple rubber "flaps" around each fan that allow air to pass through the shroud at highway speeds. It was made specifically to fit our trucks. I bought it through Old Air many years ago.

[mosel70]

Hey, I really like those!

But, the PO put a GMC grill on and the hood latch mechanism is more rounded on the aft side, different that for Chevy Grills.

I don't any of these online for '70 C10 GMC grills. Do you know of any online sources?

[HO455]

Just a couple thoughts. Is it possible at idle that much of the air is just moving in a cycle from the back of the fans over and under the radiator into the front of the radiator and the air is getting hotter and hotter when the truck is not moving? Are both fans turning the correct direction? Is the pump turning at the correct speed? Do you see good coolant flow in the radiator? When you are looking into the radiator and the thermostat is open as you Rev the motor the coolant level should drop as it is sucked into the pump.

[leftybass209]

Since this got back up to the top, I thought i'd share some information about coolant temps.

This is slightly generalized and hinges some conditions like timing which can negatively increase temps due to a mechanical disadvantage.

Engines like to run hot. The hotter the engine, the more complete the combustion process will be, the more power the engine will make and the cleaner the tailpipe emissions will be. A SBC is completely fine at 220. If it's not puking coolant, it's running fine. The cooler you run the engine, the worse the combustion process is and ultimately your gas mileage.

If you aren't boiling coolant, it's running just fine. Water boils at 212 degrees without pressure. The reason for the closed loop coolant system is to increase the temperature that the coolant boils, thus increasing its ability to cool the engine.

[MagmaJct]

You are not mistaken. What we are looking at is "thermal efficiency". Pistons move due to the increasing pressure in the combustion chamber. With that rapid increase in pressure comes heat. (Or is it the pressure come with heat?) Anything that absorbs that heat will also reduce the pressure.

Coolant that's too cold will "take energy away" from the process, reducing thermal efficiency. In addition to that, raw fuel vapor will more readily condense on cylinder walls, diluting the engine oil causing accelerated cylinder and ring wear.

I once did work on an old Mercury Cougar. The engine wouldn't warm up. Turns out it had one of those "fail safe" thermostats that ratchet in the open position if the engine were to overheat. The problem? The engine never overheated, the thermostat just decided to stick open.

More recently I was replacing a thermostat in one of my vehicles. The parts guy at Autozone asked me if I wanted a "fail safe" thermostat. I told him "no" and I commented that I don't trust them. To which he responded: "Yeah, neither do I. In fact, I don't even have a thermostat in my truck, we're in Arizona, we don't need them here."

To which I responded: "Oh-kaaayyyy"

I used to debate part jockeys in my younger years. Then I realized people like him are incapable of growing intellectually. (They learn something, but are completely unwilling to "update" their beliefs when new, more accurate, information is presented to them!)

Then there was the parts guy in the late `90s who told me not to use synthetic oil in new engines because "the pistons will fly off!"

Originally Posted by leftybass209

Since this got back up to the top, I thought i'd share some information about coolant temps.

This is slightly generalized and hinges some conditions like timing which can negatively increase temps due to a mechanical disadvantage.

Engines like to run hot. The hotter the engine, the more complete the combustion process will be, the more power the engine will make and the cleaner the tailpipe emissions will be. A SBC is completely fine at 220. If it's not puking coolant, it's running fine. The cooler you run the engine, the worse the combustion process is and ultimately your gas mileage.

If you aren't boiling coolant, it's running just fine. Water boils at 212 degrees without pressure. The reason for the closed loop coolant system is to increase the temperature that the coolant boils, thus increasing its ability to cool the engine.