my 94 z28 cooling fan doesnt come on until 230 degrees and goes off at 220 the secondary fan never comes on. I replaced water temp sensor to gauge and water temp sensor to computer. changed thermostat to new one 195 degrees seems high? unhooked temp sensor in water pump and both fans came on right away. temp does drop when I drive on road but raises at idle. any help would be appreciated. thank you and cool site. Allen

 

sounds normal to me

 

sounds normal but on the gauge on the dash it comes on right at the redline for high temp. should other fan come on also. ?

 

Have to consider any possible misscalbration of the gauge too. In the b-body the primary fan on temp is 220 or so secondary is higher and the only time it will come on is if the primary fails to bring the temp down and the temp climbs to like 240. I know some of the F-bodies used a slightly different setup turning both fans on low and then high speed based on temp instead of one fan then both, not sure which system the 94 used.

 

If you use a 160F thermostat you would eliminate much of those problems. You might have to retighten your valve covers though as they might start leaking oil.

 

Why would you put a 195degF T'stat in a car that came stock with a 180degF unit?

Stock programming is 226degF for the first fan and 235degF for the 2nd. If the first fan comes on and the temp starts to drop, there's no need for the second fan to start.

The 1st fan/2nd fan setup was changed to low speed/high speed in the middle of the 95 model year on the F-Bodys.

 

You definitely are adding to cooling problems by going to a 195° thermostat.

 

And then there's the question.... did you get the correct LT1-specific t'stat, or did you install a generic SBC t'stat, which doesn't work right in an LT1????

 

The hi/low speed dual [3 underhood relays]fans started in 'late production' 94 F body... as opposed to primary/secondary dual [2 underhood fan relays]fans which are considered 'early production' 94's..
So your 94 should have 2 fan relays, since only one fan is coming on first..
you say both come on when temp sensor is unplugged so that sounds like both fans work..
The Drivers side fan is the 'primary ' fan in 'early production 94's, so that should come on first.. also the 2nd fan should come on when you turn the AC on.. it doesnt come on much otherwise...

 

If that's the case, then why does my 94 have 3 relays, yet was built in January of 94? 3 relays in the box under the hood, yet one fan is high speed, and one is low speed.

 

My 94 is a very late production model, has two relays and only 1st fan/2nd fan. The GM PCM wiring diagrams for the 1995 models indicate that both the 2-relay 1st fan/2nd fan ("early production") and 3-relay low speed/high speed ("late production") configurations were used in 1995.

 

you are correct my car is must be early production it only has 2 relays besides the aircondition one. which make 3 yet my buddies has 4. I used the 195 because the dude at the parts place said it was oem. I have a chilton book but doesnt say which one.would that matter if the computer tells it to come on at 230 until it reaches 220. car is fine when driving around just ate slow or not moving does it climb. I get no codes at all and the computer we hooked up shows it come on at exactly 230. that seems warm to me. everything else appeears fine.

 

The thermostat's temperature rating is the temperature it STARTS to open up at. A 195deg 'stat will start to open at 195deg, and will not be fully open until approx 215deg. That's certainly contributing to your problem, compared to a stock 180 that is fully open at 200deg, or an aftermarket 160 that is fully open at 180deg.

The guy at the shop just assumed that the LT1 is exactly the same as every other contemporary GM product, and its not, because it is the only engine that GM ever used the "reverse flow" cooling system in. And he may have assumed it needs the generic SBC t'stat, when in fact it requires a very unique unit.

Again, thanks to Shoebox:

http://shbox.com/1/tstat.jpg

 

I meant 2 or 3 underhood FAN relays, not total amount of relays.. sorry..
Also, it isn't possible to have one high and one low speed fan, since 'low speed' is done by running both fans 'in series'[or at 6 volts each]and high speed is both fans individually being fed 12 volts.. if you do indeed have 3 fan relays underhood, then you have 'late' production dual high/low speed fans..
I actually am pondering altering 'early' to 'late' setup..
See below post for further info..

 

Fred, I looked into it further, and..
It's interesting to note that my 94 factory manual refers to both 'early' and 'late' production 2 and 3 fan relay setups also[no date, VIN , etc is given for further reference..]
Since it is actually IN the 94 year factory Service Manual, I assumed [ in error, it appears] that it actually APPLIED to the 94 year..
It apparently applies to the entire LT1 F Body car line when referring to 'early' or 'late' production.. not any specific year?..
The PCM A10 and A11 controls to the relay are the same for both early and late, [they both ground the relays for the same parameters etc]the change appears to be adding a relay to allow for fans to run 'in series' for low speed.. In fact I am considering changing the early to the late style [it's on the 'to do' list that never get's done here..]
Not to cut into this thread too much, but I may start a new thread [a la a 'survey' to see who has what setup, and in what year etc ] so we can confirm:
A] whether ANY 94's actually HAVE 3 fan relays[ 'late' production]
B] When the factory actually MADE the change.. [mid 94? mid 95?]
Might be interesting to know..
Shoebox fan wiring diagram:
http://shbox.com/1/fan_schematic_1995.jpg
Which I believe to be out of a 95 FSM... but my 94 FSM has the exact diagrams, also..hmmmm