Running Hot?

[McCSquare]

With the weather getting warmer (sorta) out here I'm starting to worry about the operating temperature of my K10.

The gauge reads 210 when I'm stopped at a light, and usually stays there between 15-50MPH. Sometimes it'll surge to 220. On a hotter day it hit maybe 240 and I started to panic and cranked the heater to the max.

Is that acceptable? What should I expect from a bored 350?

I'm not 100% sure that my gauge is accurate. But taking an IR thermometer to the intake manifold radiator side tanks, etc. I don't think it's that far off (based on surface temperatures being 170-205).

Should I be concerned? Where do I start? Timing, Carburetor? The pump is definitely flowing. I flushed the radiator when I first got the truck 4 months ago. It seeps a bit here and there, but no major leaks.

 

[woodsrider250]

Do you have pressure? Squeeze the top rad hose when hot...If you can squeeze it, that's bad, and can range from a bad radiator cap to much worse. For every psi you raise the pressure on a container of water the boiling point goes up.

 

[McCSquare]

Ugh. Yeah I can crush the upper and lower hose. But on the plus side, it looks like I've got 3/4s of a gasket on the radiator cap. So I guess I'll toss on a new one and hope for a "stiff hose"

Also my overflow tank is cracked and empty /non functional. That won't help either.

 

[woodsrider250]

The overflow tank is past the pressure relief, and has nothing to do w/ the pressureized part of the system. Older vehicles just have a tube directing coolant to the ground.

Bad gasket is likely a good find, and the culprit.

 

[chengny]

Check for good flow through the coolant system.

Remove the radiator cap and run the engine up to operating temperature (the t-stat should be open and the upper hose hot).

Take a flashlight and look down into the radiator through the cap mount. You should see some indication of coolant flow across the radiator tubes and into the tank on that side.

Still looking down into the RH side tank, rev the engine. Note an increase in flow and a drop in the level of coolant in that tank.

If those tests check out okay you have determined:

1. Your thermostat is operating correctly
2. Upper and lower radiator hoses are clear and not collapsing
3. The radiator crossflow tubes are clear
4. Your water pump is moving coolant as designed.

Spikes in temperature indication (that can't be attributed to coolant system components) are often caused by combustion gasses in the coolant - due to a head gasket failure.

 

[McCSquare]

The overflow tank is past the pressure relief, and has nothing to do w/ the pressureized part of the system. Older vehicles just have a tube directing coolant to the ground.

Bad gasket is likely a good find, and the culprit.

I replaced the cap and I can still crush the hose. If I turn off the engine and squeeze the upper rad hose I can hear air going out the overflow hose.

Check for good flow through the coolant system.

Remove the radiator cap and run the engine up to operating temperature (the t-stat should be open and the upper hose hot).

Take a flashlight and look down into the radiator through the cap mount. You should see some indication of coolant flow across the radiator tubes and into the tank on that side.

Still looking down into the RH side tank, rev the engine. Note an increase in flow and a drop in the level of coolant in that tank.

If those tests check out okay you have determined:

1. Your thermostat is operating correctly
2. Upper and lower radiator hoses are clear and not collapsing
3. The radiator crossflow tubes are clear
4. Your water pump is moving coolant as designed.

Spikes in temperature indication (that can't be attributed to coolant system components) are often caused by combustion gasses in the coolant - due to a head gasket failure.

When I rev the engine I can see an increase in flow and see the level shift. I also repalced the water neck gasket and hardware because I noticed a small leak.

What should I check next? Do I just have an old lousy radiator? Any other tests?

 

[chengny]

If you haven't had any overheating type problems I would look at the indication (dash gauge and associated wiring).

If you can see good flow and it's been flushed, your radiator is not the problem. Also, the fact that the level drops on the outlet side of the radiator means the water pump and the t-stat are working.

Was there any evidence of combustion gas in the coolant (bubbles in the radiator)?

As above, maybe your cooling system is fine and it's just a bad gauge reading.

If you can hold your hand on the upper radiator hose while the engine is running at operating temperature (and there are no other symptoms of overheating) I'd suspect a faulty indicating system.

Pull the t-stat out for a few days and see if you run cooler.

 

[philjafo]

Removing the tstat makes the coolant flow through the engine to fast and it doesn't pick up the heat from the motor, can actually have the opposite effect. Check the temp of the engine with a known accurate thermometer. Infared ones are ok, but I prefer a wire thermocouple type taped right to the thermostat housing. That will give you an accurate reading of the thermostat opening. Then tape it to the temp sensor, that will give you an accurate temp to compare your gage to.

 

[chengny]

"Removing the tstat makes the coolant flow through the engine to fast and it doesn't pick up the heat from the motor, can actually have the opposite effect."

I see this so often, I have to offer my thoughts.


This bit of conventional wisdom is contrary to thermodynamic/fluid mechanics principles and not true...higher flow rate of either media always INCREASES the heat transfer capacity in any heat exchanger (both engine and radiator in this case).

This is due to the reduction in depth of the stagnant layer (caused by increased velocity flow) on the surface of the tubes. The stagnant film acts as an insulation blanket which hinders heat exchange. Increased velocity of the fluid flowing across the surface "wipes away" the stagnant film layer to some degree and allows for faster thermal exchange. As someone smarter than I describes it:


(physics) A theory of the transfer of material or heat across a phase boundary, where one or both of the phases are flowing fluids, the main controlling factor being resistance to heat conduction or mass diffusion through a relatively stagnant film of the fluid next to the surface. Also known as boundary-layer theory.



But anyway; while it is true that pulling the t-stat can cause the coolant system to run hotter, it is actually due to lower - rather than higher - flow rates.

The misleading factor is actually the design of the impeller found in most automotive water pumps. It is way oversized in relationship to the maximum flow rate available through the radiator. In other words- at peak performance, the water pump is capable of moving much more water than can be provided by the total cross-sectional area of the radiator tubes.

Due to cavitation concerns, no centrifugal pump should be throttled by restrictng the intake. So, the water pump discharge side is designed to function with a certain degree of static head (resistance).

In addition to the associated hoses and passages within the block, that flow restriction includes the thermostat. Deletion of the t-stat often causes pump operation to 'go off the curve' .

Without the design restrictions in the discharge piping, the suction side of the pump is starved, the impeller 'cavitates' and total system flow rate actually drops. This reduced flow rate through the engine and radiator allows for an increase in the "stagnant film" depth and as a result, the heat transfer rate drops.

Here is the tricky part. Because of the reduction of flow due to cavtation (and consequently even less BTU's are being carried away from the engine block) the temperature of the coolant leaving the cylinder heads will rise, it will be hotter than with normal flow rates. But even though it's hotter, because of the reduced volume, there is actually less total heat being removed.

The coolant begins to overheat which increases cavitation, which further reduces flow, which increases coolant temp....

 

[89Suburban]

Also my overflow tank is cracked and empty /non functional. That won't help either.

That needs to be addressed.

The overflow tank is past the pressure relief, and has nothing to do w/ the pressureized part of the system. Older vehicles just have a tube directing coolant to the ground.

I have to respectfully disagree with that. It is there for a reason and the vehicle was designed around it being there so it should be there. It keeps air from being sucked back into the cooling system when it cools down.

"Removing the tstat makes the coolant flow through the engine to fast and it doesn't pick up the heat from the motor, can actually have the opposite effect."

I see this so often, I have to offer my thoughts.


This bit of conventional wisdom is contrary to thermodynamic principles and not true...higher flow rate of either media always INCREASES the heat transfer capacity in any heat exchanger (both engine and radiator in this case).

This is due to the reduction in depth of the stagnant layer (caused by increased velocity flow) on the surface of the tubes. The stagnant film acts as an insulation blanket which hinders heat exchange. Increased velocity of the fluid flowing across the surface "wipes away" the stagnant film layer to some degree and allows for faster thermal exchange. As someone smarter than I describes it:


(physics) A theory of the transfer of material or heat across a phase boundary, where one or both of the phases are flowing fluids, the main controlling factor being resistance to heat conduction or mass diffusion through a relatively stagnant film of the fluid next to the surface. Also known as boundary-layer theory.



But anyway; while it is true that pulling the t-stat can cause the coolant system to run hotter, it is actually due to lower - rather than higher - flow rates.

The misleading factor is actually the design of the impeller found in most automotive water pumps. It is way oversized in relationship to the maximum flow rate available through the radiator. In other words- at peak performance, the water pump is capable of moving much more water than can be provided by the total cross-sectional area of the radiator tubes.

Due to cavitation concerns, no centrifugal pump should be throttled by restrictng the intake. So, the water pump discharge side is designed to function with a certain degree of static head (resistance).

In addition to the associated hoses and passages within the block, that flow restriction includes the thermostat. Deletion of the t-stat often causes pump operation to 'go off the curve' .

Without the design restrictions in the discharge piping, the suction side of the pump is starved, the impeller 'cavitates' and total system flow rate actually drops. This reduced flow rate through the engine and radiator allows for an increase in the "stagnant film" depth and as a result, the heat transfer rate drops.

Here is the tricky part. Because of the reduction of flow due to cavtation (and consequently even less BTU's are being carried away from the engine block) the temperature of the coolant leaving the cylinder heads will rise, it will be hotter than with normal flow rates. But even though it's hotter, because of the reduced volume, there is actually less total heat being removed.

The coolant begins to overheat which increases cavitation, which further reduces flow, which increases coolant temp....

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[philjafo]

Well said Chengy, I may have been wrong on the reasoning but pulling the stat out has the opposite effect one would think.

 

[McCSquare]

Well, I'm pretty sure it really is getting hot. I thought maybe my timing was screwed up, but when it got hot today it kept trying to run when I turned the ignition off. Also the IR thermometer and the "can you hold the rad hose" test says it really is running hot.

Physics lesson aside... why do I want to pull the T-stat? What do I learn from that?

 

[MrMarty51]

I have a question:
How was the radiator "Flushed" ?
if it was with a garden hose kit,that may well be a waste of time and good water,if,the radiator is scaled throughout the cross flow tubes.
There are some chemicals that may or may not remove those scales,but,the only accurate way to get that job done is to remove the side tanks and run a rod through them,a sort of a flat piece of steel made to just fit the inside of them tubes.
Thats all.

 

[MrMarty51]

OH yeah,a "GOOD" radiator shop can flow test Your radiator,usually do`nt cost much,sometimes they`ll do it for free.
Just trake the radiator out of the pickumuptruck,take to the shop.

 

[chengny]

Physics lesson aside... why do I want to pull the T-stat? What do I learn from that?


All that discussion about running hotter without a t-stat really only applies to engines that are already exhibiting problems - or subjected to extremely heavy duty usage.

For a normal daily driven car that has no apparent problems with the cooling system, removal of the thermostat will allow unrestricted flow of coolant through the radiator. This will result in longer warm up time and cooler operating temperature under low loads.

You know that your t-stat is at least partially opening because you can see flow out of the radiator cross-flow tubes and into the cool side tank.

But, by design, thermostats vary the flow rate like a valve. They don't open and close fully and stay that way,they are in a constant state of flux. They react to the coolant temperature that is in contact with the wax-filled cylinder. However, as simple and dependable as they are, they are not infallible.

Yours may not be opening fully. If you don't want to drive without one, just take it out, throw it in a pot of water and crank up the heat.

It should be starting to crack open when you can see vapor bubbles start to form and break free of the pan.

By the time the water is boiling vigorously the t-stat should be wide open - you should be able to esily pass a pencil through the gap between the seat and disc of a wide open t-stat.


BTW - you do have a shroud installed between the radiator and the fan - correct?