Why not just remove thermostat?

[PhillipsLT5]

Originally Posted by KILLSHOTS

No kidding Phillip! Someday, Daryll, I PROMISE I'm going to buy something out of your attic!!

See you at C&C on Saturday, Phil? Daryll, can you make it?

I am planning on going early 6:30 or 7 & leaving early due to heat 9AM should be 90, maybe motor down scottsdale road to corvettes & caffeine for a water & donut

[KILLSHOTS]

Originally Posted by PhillipsLT5

I am planning on going early 6:30 or 7 & leaving early due to heat 9AM should be 90, maybe motor down scottsdale road to corvettes & caffeine for a water & donut

Yeah, I'll be leaving early too. Look forward to seeing you there.

[rkreigh]

Originally Posted by Tyler Townsley

Check the code for fueling, it runs richer at the lower temp which will contribute to some cooling. I once asked Graham why they did not calibrate the car to run at the lower temps and the answer was emissions not power. The car can make more power at 165-175 than it can at 195-205 but it could not be made to comply with all EPA emission constraints at the lower temps.

Tyler

the man speaks truth, you want warm oil and cool coolant to make power

the drag racers warm the oil in the pits and go beat on the engine right after the burnout.

and the lt5 loves cool temps

at 50 deg, the lsv puts down 525 vice 508 at 75 corrected

their ain't no dyno correction factor on the street

drive the car on a a cool dry day and report back

[Tyler Townsley]

I have posted this before but it warrants repeating. Read what everyone posts and decide what you feel is best for your situation. I have run a Ron Davis radiator and no thermostat, it ran hot. I ran a cut thermo so it was open all the time blocked the bypass and at 70 mph and 95 degree day it ran 175-185 degrees with air on. In traffic it ran 190-200 with air on. At below 65 outside the temps ran 158 just below going closed loop and any lower the heater did not put out hardly any heat. If you consistently race your car I highly recommend this setup.

Engine temperature calibration is a huge compromise to emissions. The calibration is designed to meet EPA mandated levels and this requires the engines to run at higher temperatures. The current stock system is designed to accomplish this goal.

I happen to believe engine temps should run 165-185 degrees, but that's me. I have not seen any posting that show how to get the ZR-1 to run those temps in traffic on a hot day, that includes me. I can only conclude that the airflow through the engine compartment/radiator is not sufficient enough to cool the engine to at the lower speeds.

I have a 66 and for years saw high water temps at 85 until I installed a front spoiler, this change repositioned a low pressure area generated at that speed from inside the engine compartment to just below the pan which actually draws the air from the engine compartment. This allows the air to be placed in the underside airstream and drawn away from the car.

Tyler

[Hog]

Originally Posted by A26B

Here is the location for the LT5 sensors.
.

Sorry I got my sensors backwards, the single wire CTS located in the cylinder head feeds the gauge, and the 2 wire CTS in the waterneck feeds the PCM of the L31.

The sensors you pictured are identical to the ones used in the L30/L31 305/350.

thanks for the pics, those 2 sensors should read the same temp all the time.

I'm surprised that an LT5 stat is only rated at 180º. Thats on the lower end of OEM stats.

I have to wonder if the differences between the LT5 and the L31 such as cooling capacity might be making a difference.
A 160º in my L31's trucks reads lower on the gauge and will not heat up as much as the stock 195º stat. I'm wondering if the limited cooling of the rad in the Vettes get hot and stay hot, whereas my truck will warm up letting coolant flwo through the rad and cool enough to cause the thermostat to close again?

The LT5 should ultimatley produce more BTU, but I wonder is the cooling system can transfer those BTU into the air as efficiently as an L31.
On another forum all persons who have installed a lower than stock stat are reporting similar reduction in gauge sweep visually, and via datalogging the PCM.

Looks like there isnt any advantage to using a lower temp stat in the LT5.

[Hog]

GM radiators part number and core measurements

52473260 1995 LT5-manual trans and LT1 auto/manual core size 23 9/16IN X 15IN X 1 5/16IN $224

89019344 1996+ L31 1500 core size 34IN X 17 1/2IN X 1 5/16IN
$409

Considerably more cooling capacity in the L31 rad.

[A26B]

[QUOTE=Hog;204922]...............
I have to wonder if the differences between the LT5 and the L31 such as cooling capacity might be making a difference.
A 160º in my L31's trucks reads lower on the gauge and will not heat up as much as the stock 195º stat. I'm wondering if the limited cooling of the rad in the Vettes get hot and stay hot, whereas my truck will warm up letting coolant flwo through the rad and cool enough to cause the thermostat to close again?............................[QUOTE]

Very possibly so. The Corvette radiator, angled vs perpendicular, and the fact that there are not one, but two heat exchangers in front of the radiator, combined with a very low air intake (i.e. right off the hot pavement), could all add up to more limited cooling, especially at low speeds. Add in the tendency of the Corvette to "vacuum clean" the road and collect all sorts of debris in front of the radiator and you have a pretty good recipe.

Looks like there isnt any advantage to using a lower temp stat in the LT5.

Considering the fact that the engine was designed to operate at 190F, I would say there is not an advantage to a 160F t-stat, UNLESS the engine was tuned and built for it.

LT5 engine clearances were designed for the higher temp which should also be considered. Considering thermal expansion, does 20F cooler operating temp have any detrimental effect on a stock engine with aluminum cylinders. What about a modified engine with iron cylinders and a lower coefficient of expansion? I don't profess to know the answers, but I do know from discussions with Graham Behan that the development of the LT5 was incredibly meticulous which is why no other production engine even comes close to the durability testing that the LT5 achieved. Even today, GM engineers are encountering problematic, dynamic engine issues that were noted and solved by the LT5 engineers 25 years ago.

Bob Eyers and others have made mention of cooler air intake benefits. I couldn't agree more. The increased power in cool ambient air at 40F is easily noticed in the seat of the pants. Considering the engine was designed for 190F operating temp, I would concentrate more on cooler air intake for increased Hp rather than 20F lower engine temperature.

I tend to agree with your statement, "Looks like there isn't any advantage to using a lower temp stat in the LT5." Air flow through the radiator is where the action is, not in the thermostat. Instead, concentrate on keeping the cooling system in tip-top condition. Drilling a couple of 1/8" holes in the 180F t-stat flange will help the t-stat to see direct coolant temp, increase flow through the radiator and reduce back-pressure which will retard the bypass by a corresponding amount. All good!

[XfireZ51]

I know people have made comment regarding how the motor feels stronger when cooler air is coming through the intake. I notice the same in early mornings or as fall comes to the midwest. I don't think that has anything to do with coolant temps. The motor has a MAT(Manifold Air Temp) sensor in the airhorn. The MAT sensor has a role in modifying the fuel delivery based on the manifold air temps. The warmer it is, the less fuel it can support due to density. However, one of the reasons tuners have moved the sensor and essentially "changed" the sensor to an IAT(Intake Air Temp) is that the MAT location is susceptible to heat soak and confusing the issue. By moving the sensor further forward in the intake track, the sensor is isolated from engine heat much more.
However, doing this also throws off the stock table that commands the ECM regarding how much attention it should give to air temp v coolant temps.
Part of the issue we experience with higher heat comes from this. By addressing the MAT tables, you are able to keep fueling much more consistent in spite of higher heat. When tuners move the sensor further forward, the ECM never sees the level of air temps that are assumed in the calibration. As a consequence, the motor runs richer even tho the coolant temps are higher unless the MAT table has been modified to compensate for the change. Unless you change that table, you'll never achieve a consistent tune and end up chasing the BLMs brought on by air temp change.

[SClarke1958]

I just found out about this web site yesterday and when talking to a couple ZR1 owners at the Myrtle Beach car show. Looks like a great site.

As far as whether to remove the thermostat or not, I would defiantly not. All the reasons have been mentioned in the replies already but I would emphasis a couple technical points.

1. The LT5 thermostat not only controls the temperature of the engine but limits the max pressure on the radiator inlet. When the radiator pressure is over a certain limit (about 25 psi at the radiator inlet), the bypass valve (spring disc on the thermostat) will open further and balance the amount of coolant flow to the radiator and engine.

2. The engine and thus associated controls for fuel and spark are designed to operate at thermostat control for the far majority of the engines life. So all the calibrations have been fine tuned to the thermostat control temp.

3. Coolant temp and oil temp have a relationship, so if the coolant temp is lowered, the oil temp goes down also and could cause longer term problems if too low.

Bottom line, the engine was designed to run with the thermostat and many many hours of testing went into the cooling system and engine at the design temps.

LT5 Cooling Engineer (retired)

[XfireZ51]

Originally Posted by SClarke1958

I just found out about this web site yesterday and when talking to a couple ZR1 owners at the Myrtle Beach car show. Looks like a great site.

As far as whether to remove the thermostat or not, I would defiantly not. All the reasons have been mentioned in the replies already but I would emphasis a couple technical points.

1. The LT5 thermostat not only controls the temperature of the engine but limits the max pressure on the radiator inlet. When the radiator pressure is over a certain limit (about 25 psi at the radiator inlet), the bypass valve (spring disc on the thermostat) will open further and balance the amount of coolant flow to the radiator and engine.

2. The engine and thus associated controls for fuel and spark are designed to operate at thermostat control for the far majority of the engines life. So all the calibrations have been fine tuned to the thermostat control temp.

3. Coolant temp and oil temp have a relationship, so if the coolant temp is lowered, the oil temp goes down also and could cause longer term problems if too low.

Bottom line, the engine was designed to run with the thermostat and many many hours of testing went into the cooling system and engine at the design temps.

LT5 Cooling Engineer (retired)

SC,

Welcome to the forum. Great to have resources like you available here. Any chance you know the ignition system engineer for the LT-5?