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OBD I and radiator temperature

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boblx2a

Guest
I was wondering if anyone has an idea about the reaction of the CPU in '85 Vette to changing the temperature of the thermostat. I was thinking of lowering mine from 195 (I think) to about 180. The parts guy said that would screw up the CPU readings. I don't recall any reference to radiator temperature in the OBD I readings but I have not looked at them for awhile so I could be wrong.
Anyone know about this for sure?...Thanks.........
 
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boblx2a

Guest
In retrospect I remember watching the OBD I scan tool on my computer and seeing it go from open loop to closed loop at some given temperature. I don't recall what that temperature was now but obviously the CPU does read the water temperature.
So that probably means I would need to get a new chip to move my thermostat to 180 degrees.

Can anyone verify or correct this logic?

Thanks again..............
 
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c4ever

Guest
I don't know if you'll really see any gains with just replacing the stat to a 180. Closed loop engages at about 160 (I think). I went with the stage II chip which works in conjunction with the fan. Without a lower set temp. for the fan I don't think the stat alone will make a difference. Stock setting for fan is 228:eek That was just too high for me living in FL. It now engages at 174 and I still run at 200 in traffic and 185 open road on average.
This is on my 85.
 
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boblx2a

Guest
Thanks for your response. I just needed some confirmation. I can run my laptop diagnostics and see exactly when I get home.
I was planning on replacing the switch with one that turns the fan on at 200 and off at 185. So I thought a 180 stat would fill the bill. But then the parts guy started harping about my engine staying in open loop, etc. I've messed with this stuff before on a Fiero. I used that Hypertec system with a 160 degree stat, etc. I was pretty sure it would not upset anything but I wanted to be sure before I bought the stuff. I was relatively sure that the Hypertech chip did not change the closed loop setting.

Then I was reading on the Internet about a guy asking if he could put in a 185 stat in an '88 pontiac and this tech raked him over the coals about this open loop business. So I was becoming unsure of my ground. :)

Thanks for your input...I think I can proceed now....
 
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boblx2a

Guest
I did not read your response carefully enough the first time. What is a stage II chip? What does it do and where do I get one?
This is also if for an '85....Very stock '85...........
 
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c4ever

Guest
The Hypertech Stage II, sold at various parts houses(Ecklers,MAD,etc) improves performance in a few ways. It requires replacing the stock stat with a 160. It changes the fan start temp. to 174 degrees. The car runs cooler and performs better in regards to shift and overall throttle response. I'm no genius with this stuff and others can lay the heavy tech rap on ya.
but I have noticed improvement and thats all that really counts. I do run an open air box,K&N, screens cut out,MAT sensor re-lo,throttle by-pass and modified exhaust but the car is really stock except for these minor bolt on mods. The performance improvement is noticable with little cost.
I hghly reccomend all of the above mods for good cost effective improvments.
One things for sure, closed loop operation will not be affected.:cool
Always great to meet another 85 guy. It's my favorite year(I'm a
little bias):L :L
 

Radar

Well-known member
Joined
Oct 23, 2001
Messages
200
Location
Oconomowoc, WI
Corvette
1989 Medium Blue Metalic Convertible
In response to a lower engine thermosat setting:

I also have installed the Hypertech Stage II engine management chip with a 160 degree thermostat. It works great.

The car passes emissions, gets good mileage (26 mpg +-), and has excellent power. The chip changed the OBC fan cut-in temoperature to 174 degrees. The car has much better low speed throttle response and is much stronger from the hole.

I would not go back to the stock chip.

Radar :)
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
All you need is to add a three wire O2 sensor and you can run the car as cold as you want and the computer will still slip into closed loop.

Trust me on this one. In fact, my 90 runs tooooo cold. I need to work on heating it back up, and yet I am in closed loop by the end of my street each morning.

TPIs can send one out to you with the weather pack plug. All you do is add a 12+ key on power to one wire, ground to the other, then hook the signal wire up to your stock computer single wire O2 signal.

You swap the sensor in the exhaust and that is it. If it takes you more than 20 minutes, then I would be surprised. you will spend more time looking for a nice neat way to wrap your new wires up tight. I used the 12+ wire that goes out to the cooling fan relay to tell them the car is on, and I grounded the other to the chassis.

This is a $60 or so mod that will make a world of difference in performance as you drop the temps, keeping the computer happy.

Basically years ago it was thought all you had to do is stay in open loop for the most performance. Well, this is half true. In reality the best performance comes out of your engine when everything is in synch.

Good luck.
 
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boblx2a

Guest
Oh yes, the old Hypertech solution. Now I remember, takes awhile for the cobwebs to fall off. :)
We ran those in my Fiero days. That's before I chased a Vette off of a ramp to a freeway and he left me like I had slammed my brakes on! I said to myself, I need to get me one of those. I did and never looked back. :)
We ran the chip and the 160 degree stat. The theory went something like: The water going through the throttle body jacket became cooler so the air going through same became more dense and provided more power.
When we dumped that particular chip (the one for the Fiero) we learned that all it really did was increase the spark at WOT.
But that spark increase was handy so I left the chip in but changed the stat to a 180, 160 was a bit chilly.

Thanks for the reply, I appreciate it............
 
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boblx2a

Guest
I suppose there must be other peramaters changed in the Vette's Hypertech chip if the fan comes on at 174 degrees.

I was planning on using a new switch that cuts in at 200 degrees and off at 185 degrees and maybe a manual switch, just in case. :) Plus the 180 degree stat. What scared me off was that parts guy and that techy's reply to the guy with the 88 Ponitac who wanted to lower the stat temp.

With the help I have received I am convinced that lowering the stat to 180 degrees is probably not going to make any earth shattering problems after all.

I have scanner software for my laptop for both OBD I and OBD II so I will know if something doesn't play right.

A 3 wire O2 sensor, wonder what they'll think of next. That sounds like a good idea in any case.

Thanks for all of your help guys..................
 

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