theadmiral94

With all the discussion about the ‘high’ running temperature of these engines, I have realized there is a different placement of the temperature sensor versus the thermostat (temp sensor is in the water pump outgoing hot water out-flow to the radiator, whereas the thermostat is also in the water pump, but it is instead in the incoming cooler water in-flow from the radiator).

Therefore, isn't the dash temperature ‘misleading’ regarding the thermostat as it will always be higher than the thermostat?

Case in point, I am assuming our car has the stock 180* thermostat, yet the dash shows 205* as the temperature it warms-up to quickly and therefore presumed to be the temperature the thermostat is trying to maintain (I know the thermostat only limits the low end of the engine temperature)?

Has anyone determine the difference in temperature between these two locations on their LT1? Does it match ours?

If older, non-reverse coolant flow engines (e.g. L98) had their temperature sensors in the traditional location of thermostat housing’s outgoing hot water flow to the radiator, wouldn't the dash temperature have been more in line with the thermostat and thus not have as ‘misleading’ a dash temperature (during initial warm-up of course)?

So, doesn't this all mean that assuming the same thermostat, that the dash temperature of an older engine (e.g. L98) will always be cooler than a reverse-flow engine (e.g. LT1) by design, based on the thermostat and sensor location and the coolant flow direction and that the higher temperature may not be the result of radiator problems?

Any/all input and thoughts would be appreciated.

I should close by saying I am about to do a complete coolant system service. I have already decided to use a 180* thermostat, completely flush the cooling system, remove the radiator and clean its fins and the AC condenser’s fins, so no need to open-up that ‘can of worms’.

Also, Our 94 LT1 Coupe runs around 201*-210* with the AC on, while moving and standing still, and from 205* to 230* with the AC off, depending on whether the car is moving or standing still. All during ambient air temperatures from the 70’s to the 90’s. I am assuming the stock (180*) thermostat is installed. Also the oil temperature is typically higher by 10*-20* (using Mobil-1). 97k miles. New air dam. And, without removal, Radiator and AC condenser and in-between cleaned of leaves & road debris using vacuum and tooth brush.

Best Regards.

jrzvette

The temperature rating of the thermostat is the temperature at which it opens. Unlike a thermostat connected to the heating and cooling system of your house, the thermostat in a car's engine does not "maintain" any temperature, that is the job of the cooling fans and the cooling system in general. The car's thermostat is simply a valve that keeps part of the cooling system (the radiator) out of the loop until the predetermined temperature is reached.

FELNGR8

No opinion on LT1 vs. L98 readings. I'm told the LT1 runs hotter by design because that's good for emissions. Not for power or engine life. Flame suit on.

I have the 160 thermostat and a radiator completely cleaned one year ago. In really hot weather, ambient 95-100, my engine while moving at speed runs at 195 degrees with the fans set at normal on-off settings. At idle in really hot weather it jumps to 227 very quickly, then cools down quickly when I move. I had been running altered fan settings that had the engine max out at 195 degrees but had trouble passing the emissions test in July with those settings.

My engine definitely runs stronger when cool like at 185 degrees max in the staging lanes. But no harm is done to the engine to run hot, just the power sucks.

SJW

The LT1/LT4 thermostat is in the same place, functionally, as in the Gen 1 SBC engines. It regulates flow from the water pump, into the upper radiator hose, and then on through the radiator. The coolant flow through the LTx engine is reversed relative to the Gen 1 SBC, but the flow through the radiator is not reversed.

It's not at all uncommon to see a temp difference of 20 to 25*F between the t-stat opening temp and the operating temp with the A/C off on the open road. This is very typical. You have correctly noted that the t-stat only sets the temp threshold at which the radiator enters the picture. So, yes, expect to see the ECT running ~20*F or more above the t-stat rating. It's not misleading, as it's reporting the true ECT, and is in no way attempting to report the t-stat threshold.

Oil temps typically do run ~20*F higher than ECT, under normal driving conditions, so what you're seeing is normal.

It's worth also knowing that there are two temp sensors on your LT1. The one in the water pump reports ECT to the ECM, which will then in turn report that ECT data to the digital display on your IP, if that's the readout you select. The second temp sensor drives the analog temp gauge on your IP, and IIRC, it's located on the rear of the driver's side cylinder head (if it weren't so late, I'd verify this location, but...). The sensor in the water pump, and therefore also the digital readout on the IP, are generally regarded to be more accurate than the analog gauge and its sensor.

I responded to your operating/fan-on temp question in your other related thread.

Be well,

SJW

Tom Piper

You are are correct.

The one thing to keep in mind is the digital temperature sensor that is located in the out-flow of the water pump is used for both the digital readout and as the coolant temperatur sensor (CTS) for the ECM.

The LT1/LT4 coolant flow starting with the radiator is:
1) From the radiator through the thermostat in the water pump.
2) to the heads -- the analog temperature sensor is in the right head.
3) down through the block
4) back to the water pump -- this is where the digital coolant temperature sensor is
5) back to the radiator

When the thermostat is closed, the bypass valve opens that allows the water pump to keep circulating coolant through the heads and block while bypassing the radiator.
When the themostat is open, the bypass is closed forcing the coolant through the radiator.

So, this would be a likely scenerio:
Coolant coming in through the thermostat = 180 degrees
Coolant picks up 15 degrees of heat from the heads and block.
Digital temperature sensor reads 195 degrees.

Tom Piper

FD2BLK

Keep in mind that you want the coolest heads posible but the block temp is fine a bit hotter as long as no dammage is occuring. Both my digital (Water pump) and analog (head sensor) read with in 5 deg of each other.

SJW

Sigh... I gotta stop responding to technical posts after midnight.

My post SHOULD have said:

Coolant flow in the LT1 radiator is not reversed, but the thermostat regulates flow from the radiator into the water pump.

My apologies to theadmiral94 for the erroneous reply, and my thanks to Top Piper for correcting me.

Be well,

SJW

theadmiral94

Much thanks to everyone for their answers and confirmation of my observations.



P.S. to SJW, no apology needed, I noticed the hour of your reply and disregarded the very small error. Thanks again.

cspano

Hi:
Just for what it's worth I bought my first Vette, a 93 Coupe, in April this year. I am old school when it comes to water temp and was very concered with the 230 plus temps. I live in South GA where 100+ is the norm in the summer. Well I pulled the radiator to clean it found a small seaper crack in the plastic tank replaced all hoses, new Auto Zone radiator ($190.00 life time warrenty), new 180 stat and two cans of a product called 40 below. Car now maitains 185 to 190 with the A/C on in traffic in 98+ heat. Stays dead on 186 on the Interstate with or without A/C. FYI when I pulled the radiator it looked like a stone wall, it had so much dirt in it