im buying a 1984 with a 4+3 from my father in law and he had put a 170 degree thermostat in it now the overdrive will not work because of engine temp, is there a different sender you can get to fix the problem or go back to a 190 thermostat, i have never owned a vette before so all new to me, always been a chevelle guy

 

Go back to the original temp thermostat. There is no need for a 170 degree 'stat. And because the '84 OD requires a 176 degree coolant temp to work, the 170 'stat is the problem.

 

i'd think it difficult to blame the t'stat for non-working OD. I'd think regardless the t'stat the car sees very likely temps to satisfy that aspect of operation. I'd think you would need to address complete diagnostics. Maybe just an ECT sender for a start. If you can't validate the temps the ECM is seeing I'd think it hard to blame t'stat 1st.

OP do you have the FSM and have you actually confirmed that the ECM isn't seeing sufficient temps.

Maybe if it has the older 'button head' ECT you just update it and use maintenance as an excuse.

I've read I believe different temp requirements from different individuals. I didn't confirm in a FSM so .........................?

 

I can confirm my 84 needs to be 176 degrees before the od will engage.

 

 

Yes but in 85/86 I think they lowered it to 140 or something since the 176 was pretty high.

 

Here's a link that shows the minimum coolant temps to operate the OD by year. The temps are shown at the top of the chart.

 

 

I'm not questioning the 'requirement' but I'm finding it somewhat hard to believe that regardless of cooling system maintenance that an '84 L83 isn't making 185° + under typical conditions even with the 170° 'stat

OP - Have you verified the ECT/CTS or whatever you'd like to call it? Have you had a scanner on it?

I'd think it much easier for initial diagnostics to confirm ECT/CTS function before jumping to a t'stat solution. Is the 'stat the solution? Maybe in the end yes.

What does your ECT/CTS look like? If it's not a 2-wire 'newer' service part I believe it would be my first replacement. Regardless of design I'd do an Ω check before run after sitting maybe a couple days and then after a good run. The FSM has expected values.

This would be original and removed from service many years ago.



This is the newer and preferred



If checking a dealer some old stock 10045847 would be the sensor and also the connector. I was able to get one not long ago from a local dealer.

You could use this resistance report of an OE/Delphi that's very popular and would be correct or it's current service replacement. Since it's an 'emissions device' tolerances are fairly tight.

http://pe-ltd.com/assets/coolant_temp.pdf

 

I can confirm it's 140 for the '85. I went with a 180 tstat to keep the temps down a little bit for day-to-day driving, that could possibly work for you as well. I had a stock one in there for a while though and never had any issues.

People always talk about the thermostat like a lower one will solve their overheating issue. It DOESN'T. It changes the MINIMUM temp your engine will run at. If you're overheating, you need to flush the cooling system. Check for debris in front of the radiator. Stuff like that. Opening the thermostat sooner won't actually make your engine run any cooler.

Sorry for the rant, just trying to help

 

I run a 180 and still have issues, it drops in and out at any ambient temp below 75 or so.

I hear you, but even on 90 degree days I more or less run at or near the thermostat... (~180-185) below 75 degrees and the ecm reads the temp (computer not dash) in the manifold at 173. Could it be an issue with the new delco sensor? Sure but the dash reads 2 degrees higher only so I doubt it. Could be the new thermostat being a 180 too. I had the original style sensor until I replaced my intake manifold last summer. The connector disintegrated in my hands when I removed it. I always found the CFI cars to run a little cooler than their TPI counterparts. My cousins gta stays around 200 no matter what the ambient temp is.

I am not arguing with you, I am just saying that in my experience the 84 needs a 195 degree t-stat to have the overdrive working the way it should. When my old one stuck open on a 60 degree day I could drive at 55 for a couple miles with od off and be down in the 155 degree range. The stat only stuck open the thickness of a quarter. It actually surprised me it would stay that cool. Once stopped it would go back up to 200+ but it would come right back down. Don't take it the wrong way, GM probably lowered the engagement temp for a reason. It is the only issue I had with the unit.