13 replies to this topic

[Wirra]

I am installing an LS1 motor in a 70s sports car and I'm about the connect the heater hoses.

 

Like all earlier cars I'm familiar with the tap on the 70s sports car is placed in the inflow line to the heater and adjusted to monitor the amount of hot water permitted to flow into the heater core. I assume back pressure limits the amount of hot water being feed into the heater inflow hose at the engine.

 

On the LS1 motor, and it seems quite a few other motors, the hot water flow from the engine is constant and that which is not required to flow through the heater core is redirected back to the engine via a return hose.

 

What is the purpose of this 'loop' circulation and might changing to the simple restricted inflow system create issues? I assume there is something in it otherwise why would manufacturers go the the extra expense of the 'loop' system. Thank you.

[GreenMachine]

Can't speak for the Chev, but on the MX5 that flow is important for the cooling of No4, the reason being that outlet is all that remains of the way the head was designed to flow (in FWD configuration), the switch to longitudinal also involving a switch of the outlet/thermostat to the other end of the head.  Particularly on competition engines, and especially turboed engines, that loop provides a necessary function (even when the heater is 'off'), preventing poor flow/stagnation around No4.

[GBarclay]

I am not 100% clear on exactly what your question is, but .....

 

in my experience with LSX motors used in off road racing vehicles, I can relate the follows

 

- we have no need for a heater core in an off road machine, but simply blocking the heater core ports on the water pump can cause issues with the thermostat not opening reliably. We source a u-shaped hose (from Summit or Jeg's) which essentially bypasses the heater core, but allows the thermostat to function as designed, (you need hot water on the back side of the t-stat to get it to open). 

- removing the thermostat can cause it's own issues. Simply put it acts as a restrictor in the cooling system, slowing the flow of water and allowing an adequate exchange of heat in your cooling cores. Removing the t-stat allows the coolant to pass through the radiator too quickly and there is not sufficient exchange of heat. Gutted t-stats work just fine. 

- I don't think you will experience issues mentioned by GreenMachine on a LSX, but you will need to pay attention to the steam ports in a LSX cooling system. Failure to do so will result in a cooling system that does not bleed properly, and can have hot spots in the cylinder heads (driver side slightly more prone to this). How you route the lines in the steam ports will depend largely on the location of your radiator. With rear or bed mounted coolers where the cooler is the highest point in the system, we drill and tap a hole into the top of the water pump, thread in a t-fitting, and connect the steam ports to this. If the radiator is lower than the highest point of the engine cooling system, you will likely need to go with a pressurized header tank, and can vent the steam lines into the overflow part of the header tank. 

 

Once the engine is up to temp (t-stat open) I can pinch that u-shaped hose closed, and it makes no difference (at least visually obvious) to the operating temps. My guess is that the coolant will follow the path of least resistance, so if your restriction in the heater circuit is too much, the coolant will flow to the radiator instead, leaving your cabin air cooler than you like. 

[Greg Locock]

Never really worked on the fluid side of HVAC units, but running a waterpump into a throttled valve will cause erosion (from cavitation) and noise. So diverting the flow around the heater core may allow them to use thinner metal in the core and piping.

 

Thermostats used to have little jiggler bypasses on them which allowed some hot water to get around the back and warm the capsule. 

 

Many moons ago as an intern i designed the cooling circuit for the ECV3 economy car, in order to get fast warmup i took the cabin heating water from the radiator side of the thermostat. No. Not acceptable. They junked all of that part of it and kept my rather neat flap over the cold air intake duct for the rad, based on R/C wing construction, balsa over a foam core. So that was my first ever car part to get made. 

[Kelpiecross]

I have never been too sure about the theory of restricting the cooling water circulation flow to allow more time for cooling in the radiator etc.  I think logic would say that in a closed loop circuit the overall average time the water spends in the radiator  (or the engine)  remains the same.  If it passes through the rad. quickly - then it returns more quickly to the rad. having picked up less heat in the engine.  Having the water travel more slowly may allow more time for cooling in the rad. - but it also allows more time for heating in the engine - so the result is the same - except that if the flow is slow  the water may reach boiling point in parts of the engine.    It shouldn't make any difference in theory - but my personal experience (in older-type cars) is that removing the thermostat to speed up the circulation actually does help with an engine that is marginal in its cooling capacity in very hot weather.  A faster flow should give more even temps. throughout the engine. 

[gruntguru]

Faster flow increases the cooling system capacity by reducing the delta T (water) across the radiator. This allows the average temperature of the radiator to be closer to the maximum engine temperature allowable.

[Lee Nicolle]

I have never been too sure about the theory of restricting the cooling water circulation flow to allow more time for cooling in the radiator etc.  I think logic would say that in a closed loop circuit the overall average time the water spends in the radiator  (or the engine)  remains the same.  If it passes through the rad. quickly - then it returns more quickly to the rad. having picked up less heat in the engine.  Having the water travel more slowly may allow more time for cooling in the rad. - but it also allows more time for heating in the engine - so the result is the same - except that if the flow is slow  the water may reach boiling point in parts of the engine.    It shouldn't make any difference in theory - but my personal experience (in older-type cars) is that removing the thermostat to speed up the circulation actually does help with an engine that is marginal in its cooling capacity in very hot weather.  A faster flow should give more even temps. throughout the engine. 

Aaaahh. A thermostat or at very least a restrictor is the most important part of the cooling system. An essential.  No t/stat and an engine that will run far too cold when driven slowly and far too hot when driven fast. And heads will crack, even inserts fall out as the uneven temperatures cause havoc.

The only time to EVER remove a thermostat maybe is if the radiator is nearly blocked solid. Though in reality it will make no difference then as it will be wide open anyway.

With a thermostat [they can cause grief on occasion] working correctly you can control the engines temperature. An engine running cold has increased piston rock which wears out bores. Plus the ring gap is too wide. Warm the engine up no appreciable piston rock and closer ring gaps. Yet alone the head cracking and even block cracking associated with cold engines. Exhaust valves, the top of the cylinders, the pistons are all critical to stable controlled heat. The heat differences is what cause heads and blocks to crack and inserts to fall out

And yes I have seen all of the above, often! And a controlled  cooling system too is critical for heater operation.

Over cooling does far more damage then overheating.

[saudoso]

Faster flow increases the cooling system capacity by reducing the delta T (water) across the radiator. This allows the average temperature of the radiator to be closer to the maximum engine temperature allowable.

And increasing the delta T between the fluid and both the radiator and engine walls.

[Kelpiecross]

"Over cooling does far more damage than overheating"?    I'd take the over-cooling if I had a choice.    You certainly need a thermostat in winter - but not in hot weather.  My opinion is that an engine only needs to be about 70 to 80 degrees C  - it doesn't need to be 95C or so.

[GBarclay]

I have never been too sure about the theory of restricting the cooling water circulation flow to allow more time for cooling in the radiator etc.  I think logic would say that in a closed loop circuit the overall average time the water spends in the radiator  (or the engine)  remains the same.  If it passes through the rad. quickly - then it returns more quickly to the rad. having picked up less heat in the engine.  Having the water travel more slowly may allow more time for cooling in the rad. - but it also allows more time for heating in the engine - so the result is the same - except that if the flow is slow  the water may reach boiling point in parts of the engine.    It shouldn't make any difference in theory - but my personal experience (in older-type cars) is that removing the thermostat to speed up the circulation actually does help with an engine that is marginal in its cooling capacity in very hot weather.  A faster flow should give more even temps. throughout the engine. 

I can only relate my experience with LSX engines as I have actually dealt with these issues. 

 

I agree that on older type cars, a hot rod trick was to remove the t-stat, but in my experience this was only done as a last resort type of thing, or done to get the car through one particular race. It was a band aid, not a solution. 

 

For LSX motors, which is what the OP was asking about, it is well known that removing the t-stat can cause more issues than it solves. From personal experience I can sure say that pulling a t-stat on a LS6 dry sumped motor with rear mounted radiator will result in engine overheating at idle in average temps (no moving airflow, and no radiator fans engaged). Re-installing the t-stat solved this issue immediately, and while I was certain the cause was more involved, it really was as simple as the rate of flow being too high sans t-stat. Simply checked with an IR thermometer measuring radiator in vs radiator out temps. With no restriction in the system, the in vs out temp delta was pretty small, once the t-stat was in place the delta was a lot more pronounced (this was about 5 years ago, so I apologize for not having the exact figures in my memory, but it was in the 30 - 40 range once the t-stat was in place). Measuring temps in and out at the water pump would have been more accurate, because we used aluminum tubing to transfer coolant to the radiator in the rear, and we were shedding a significant amount of heat just through the tubing (by design)

 

So I would have agreed with you that in "theory" it should not have made a difference, but in reality (with an LSX) it sure did. 

 

Sure in most of our applications we are putting the motor under far more stress than a street driven vehicle will ever see, so some of these issues might never appear on a daily driver or weekend driver. 

 

Don't forget that all the LSX motors I see are run off a GM ECU or GM-clone ECU. If the temps are not correct the ECU is going to attempt to compensate (it is programmed to expect a t-stat in the system) and at the least the motor is going to run rough with poor economy, and terrible emissions. One of the tuners I deal with has programs for LSX motors that are run without t-stats, but this is exclusively for drag racing applications, and the motors are pre-warmed prior to firing them up. 

 

I am not as smart as some on this forum, so will leave the theory to those, but in practical applications I can attest to "slower coolant flow equals better temp delta's" in LS applications. As always your experience may vary

Edited by GBarclay, 28 October 2015 - 17:20.

[GBarclay]

Something to add to this thread that not everyone may be aware of

 

On SBC engines the t stat is located on the water pump outlet. 

 

On LSX engines the t-stat is located on the water pump inlet. I have sometimes heard it referred to as reverse coolant flow (though that is technically not correct)

 

Rather than clutter the thread with my (sometimes useless or lack of) knowledge I will just refer the OP to 

 

http://www.pirate4x4...avista/Cooling/

 

It is perhaps the best collection of information on cooling, specifically relating to LSX engines in one place that I have come across. Hope it helps the OP with his question

[Wirra]

My thanks to all who have posted.

 

It would appear from the above comments and information gained elsewhere that placing a valve in the heater inflow hose, and not creating a loop, will not lead to catastrophic failure. However. while no definitive answer, either here or elsewhere, has been forthcoming as to why GM included a loop system I intend to take the conservative approach and establish such a system. Again, my thanks to you all.

[Lee Nicolle]

Something to add to this thread that not everyone may be aware of

 

On SBC engines the t stat is located on the water pump outlet. 

 

On LSX engines the t-stat is located on the water pump inlet. I have sometimes heard it referred to as reverse coolant flow (though that is technically not correct)

 

Rather than clutter the thread with my (sometimes useless or lack of) knowledge I will just refer the OP to 

 

http://www.pirate4x4...avista/Cooling/

 

It is perhaps the best collection of information on cooling, specifically relating to LSX engines in one place that I have come across. Hope it helps the OP with his question

Good article.

[Lee Nicolle]

"Over cooling does far more damage than overheating"?    I'd take the over-cooling if I had a choice.    You certainly need a thermostat in winter - but not in hot weather.  My opinion is that an engine only needs to be about 70 to 80 degrees C  - it doesn't need to be 95C or so.

It is designed to run at at least 90C. Less is just wearing it out and with efi engines probably making it rich too.