FAST and coolant temps?

[96Z28SS]

I have a 396 stroker with a FAST system.
I'm wondering which temp sensor is the FAST looking at is it the one in the head or the one at the waterpump, cause the numbers aren't matching.

I have a 170 thermostat in, the fans turn on at 175 and Fast says the coolant temp is 200 the factory gauge in the car is reading 190.

When driving the car watching the temp on FAST I've seen temp go to 203. When i come to a stop the temp goes down to 180ish.

Does my electric waterpump not flow enough?
Which temp sensor is FAST reading?

 

[Superskwrl]

I would think the 1 in the head, but odviously depends how the car is wired

 

[Lonnie]

If you have an LT1 car, it is the one in the waterpump.

The one in the head operates only the gauge. Remember the factory gauges are not that accurate either.

 

[96Z28SS]

I have an LT1, so okay it reads the one at the pump.
Why is the temp at 200+ when i have a 170 t-stat in.
Motor cools down at idle (185)but while driving it gets hotter (203).

Is the electric water pump not flowing enough?

 

[96SCTA]

Mine reads about the same. The gauge is just not to accurate about 10-15 degrees off.

 

[Chuck Leeper]

Huh??

Originally posted by 96Z28SS
I have an LT1, so okay it reads the one at the pump.
Why is the temp at 200+ when i have a 170 t-stat in.
Motor cools down at idle (185)but while driving it gets hotter (203).

Is the electric water pump not flowing enough?

Electric pump?? Did you put it on?
If the temp climbs at road speeds, it may be that the lower airdam is gone, and the air flow is not directed at the rad as it should be. The dam is not in the pic at idle, so the no load heat from the engine is handled by the fan..

 

[Chuck Leeper]

head sender...

Originally posted by Lonnie
If you have an LT1 car, it is the one in the waterpump.

The one in the head operates only the gauge. Remember the factory gauges are not that accurate either.

As Lonnie said, they are not real accurate. We find that the reason is the location of the sender in the head exposes it to far too much exh system heat.
I just moved one on a streetrod that has a Tune port engine in it..I put it on top of the intake, and the gauge became much more steady and accuracy improved a bunch...

 

[96Z28SS]

The air dam is still in place and isn't modified in any way.
I put a Meziere electric water pump in. Already checked the wiring and its correct.

I think the pump can cool the car at idle and then when I start driving the pump stays at its constant flow which it may not flow enough to cool at driving speeds.

I'm just wondering what you guys think.

 

[Chuck Leeper]

Could be..

Originally posted by 96Z28SS
The air dam is still in place and isn't modified in any way.
I put a Meziere electric water pump in. Already checked the wiring and its correct.

I think the pump can cool the car at idle and then when I start driving the pump stays at its constant flow which it may not flow enough to cool at driving speeds.

I'm just wondering what you guys think.

I'm thinking the same thing.. pump speed is constant.. May be a bit too much/OK for idle, but not enough for hi loads and hi engine speed.. Some of those pumps are not intended to be on the street for extended run times...??

Also, is that a reverse flow system?? Any issues there??

 

[96Z28SS]

Its a reverse cooling but its spinning or pumping in the right direction.

 

[Lonnie]

I also experience some variation from the gauge to the FAST reading. Anytime you have 2 readings from different locations, they will differ. The factory gauge is junk (seems like it has a big dead band). If it reads between the second & 3rd lines you are not hurting anything. As far as correlating the lines to values... don't. For a test hook an Autometer Gauge there & see what it says..... at least it will be pretty accurate. (The car does not need this connection to run)

Your engine will typically run at a higher reading than your stat setting... often by 10deg+ on the LT1 A stat starts to open at the rated temp & is generally fully open at 5deg hotter.

A 396 with stock rad will have marginal cooling at highway speeds. My 383 LT1 is happy if under 85 outside, above that it tends to climb equally with the outside temp.

200 to 210 will not hurt the motor & remember the heads are cooled first (due to the reverse cooling) , so the water leaving the pump is hotter than the heads. Mine runs in the 190's typically & took me to work (60mi round trip for 3 years) while running 10's. It used to run at 210-215 in stopped traffic when the intercooler was under the car blocking the rad airflow.

I have seen some problems with the electric pumps & am still reluctant to use one on mine for that reason. Some have good luck, some do not. Wish I could blame your pump, as I am fighting the urge to use one during my next heads/cam swap. I want the extra few HP as well, but do not want it to get hotter that it is now. For reference, what pump do you have?

I run the stock rad, single 16" Spall fan (running continuously to keep air movement through the intercooler) & a Hypertech stat. I would guess that the stock fans pull slightly more air. Mine usually gets hotter in traffic than when idling. Try buying a longer undercar spoiler (Wings West has one) that is closer to the ground. A heavy piece of 3 to 4 ply corrugated cardboard & duct tape can make a temporary test piece. Make it about 2" longer... It will catch more air at speed & may help cool it down.

 

[JrTuner]

Every LT1 i have ever seen with a FAST on it the temperature is always higher than the gauge. If you look at a stock ecm car with a scan tool you will probably notice the same thing. I think this is due to the fact that the water is hotter in the water pump than it is in the head especially since it is reversed cooled. As long as the coolant temperature is stable and consistent I wouldn't worry about it.

 

[96Z28SS]

Lonnie,
I have the standard Meziere Electric Waterpump. This is what gets confusing. On the manufacturers website it claims 42 gpm and on all the vendor websites i go to it says 37 gpm, I even saw it in Summit magazine it lists it at 37 gpm.

So which is it? Did they change the pump ?

Anyways i also see they have a heavy duty version that pumps 50 gpm.

The only reson I went to the electric waterpump is because on the LT1's you can't run a double roller chain and retain the use of the stock pump you need to run the stock chain or the LT4 chain, but I heard problems with stretching so i went with a Cloyes chain and had to get rid of the waterpump drive gear.

I might just go and buy a heavy duty unit and see what happens.

Also the guage in the car starts at 160 and the next line is 190 and it never goes past that line.


Rob