Not sure why content doesn't post in the initial creation....
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My first forum post.... Bare with me 😁

I've been having engine cooling issues. The stock temperature guage works but I'm getting some nasty running issue I've been battling since I purchased the car from the 2nd owner in 2020.

The engine runs great, always checking my guages and on the freeway the stock guage will always be at or around 160* but driving more than 15 minutes, the engine will start missing/backfiring (i.e: exiting the freeway from a srop/start. It's so bad I have to gently limp it to a lot or safely off the road. I then have wait 15-20 minutes before it will run well again. I have been through just about everything (sensors, new Opti/plugs/wires/coil/ICM) but I started chasing the cooling system.

I just pulled the thermostat and found it's absolutely the INCORRECT style for what appears to be a standard Chevrolet small block. I believe with the wrong thermostat, the engine coolant isn't able to properly flow from the radiator--in to the engine. I took this path because I used my infrared temp gun in these spots:
1. Water neck (193*)
2. Upper radiator hose (cool return side at 163*)
3. The radiator in general (137*)
4. Lower hose (hot outflow at 130s*)
5. 3 core radiator is pretty well 130s*

My issue right now is the o-ring on the new LT1 specific thermostat fits but it's not exactly flush. I've lightly oiled it as I've done hundreds of times as a former auto mechanic. Including pics and hoping someone has experienced this concern here lately. Mishimoto brand (avidly used this on the 6 Fox Body Mustang 5.0L for years. What I pulled out had a part number, barely legible and it traces to Robert Shaw's website--part is a FlowKooler thermostat. Nowhere on their site does it list a Tstat for an LT1 and besides, there's no lower plunger to seal the opening in the pump housing (stock housing).

Any help would be fantastic in advance!

​​​​​​​Jon

 

Not sure I interpreted your questions correctly. I apologize if I misunderstood, it’s been a long day.

Here's a photo of the typical Hypertech LT1 replacement (160°F). It appears to somewhat match the one on the right in your photo. They both have the plunger to close the bypass in the water pump. Note that the plunger is retracted when the t'stat is closed (cold), and extends as the t’stat opens up. But it is unclear if all the dimensions are correct.

Or maybe you were just noting that the oddball t’stat you removed lacks the plunger.

The 160°F t’stat, (stock is 180°) with reduced fan on/off temperatures programmed in the PCM generally results in a cooler running engine

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

As far as the O-ring on the correct LT1 piece, I don’t recall it sitting flush with the water pump flange. Lacking a gasket, it has to project slightly to form the seal against the water neck.

Would be very unusual to experience the engine running rough and misfiring/backfiring with the dash gauge indicating 160°. The engine was designed to run at 210°, midpoint on the gauge. If you haven’t already done so, might be worth checking the accuracy of the sensor/circuit (driver side head) for the dash gauge, and the sensor/circuit (bottom of water pump housing) for the feed to the PCM.

4th Gen LT1 F-body Tech Articles

 

Thank you for the reply sir!

The o-ring when removed from the Tstat sits inside the beveled surface perfectly but when it's on the Tstat, it simply won't sit flush. Taking into consideration your thoughts, maybe you're right and it should fit flush.... Maybe if it were flush the neck could compress the o-ring. I'll go ahead and drop it and torque the neck to spec then.

*To note, when the backfiring/running poorly occurs, the temp guage isnt even at the mid mark and jumping out with the infrared gun shows discrepancies. Just been a very horrible battle!

 

I think the O-ring top should be a bit above the surface of the water pump flange. In any case, it's got to compress between the two flanges to effect a seal. That assumes the neck flange is flat, or even slightly concave. If the neck flange has a projecting rim that fits inside the pump flange, it just has to contact the O-ring and do some compression. I changed my t'stat 25 years ago, and sold the car last year. So my memory of the process is vague at best.

What year is your PCM. Have you scanned it for codes? Alternatively, if you are running a 94/95 OBD-1 PCM you can use (free) Scan9495 software to data log and look at what's happening when the problem occurs. I've been able to help with some logs. The presence of the S/C makes it a bit beyond what I normally see, but it might be worth a try. There is also a free OBD-2 scan software, by the same author, but the data is not as thorough as the OBD-1 version.

 

IIRC, the t-stat sits in the groove, but it's not flush. Like Fred indicated, it needs a little compression to be able to seal.

 

Thank you both for your knowledge and insight, highly appreciated.

I will proceed with installing the Tstat and torquing it down tomorrow after work. I had a thought and a memory from 2021....I found coolant would seep from the base of the water neck and I was even able to squeeze the cool side (upper) hose and coolant would seep out. I live in Milwaukee and the day I stored it, it was about 40* outside and showed my buddy that I could squeeze the hose and coolant would seep and it did. Then I thought about it more, the running issue has NEVER happened when the temperature outside was under 50*. This is why I previously stated I turned to chasing the cooling system......

Fred,

I purchased Tuner CATS' logging and tuning software in May. I'm still learning how to properly use both but right now focusing on the logging side. I've checked some PIDS and checked codes but I mostly found historical codes after replacing the Opti etc. and nothing related to the the cooling system. I did purchase an ECT sensor, I believe that's the one located in the pump housing, bottom right.

 

*UPDATE 10/12

I had previously replaced the thermostat with the correct LT1 style type, decided to replace the ECT while I was in there and properly bled the system. I've already driven the car a few time since.

I decided to data log yesterday after getting DTC 23 (MAT sensor low) the last time I drove it. While logging, I noticed the Coolant Temp PID showed the engine at 212* but my electric fans didn't even kick on, which are set to 185*. I shut down and used my thermal gun and no spots I tested were even over 200* (upper hose, housing, neck etc.) but the PID in Tuner Cat insisted the temp being read was now at 215*. Car was idling under 15 minutes as well. To me, something seems very off.

I assumed Tuner Cat reads the ECT and not the one-wire dummy gauge sensor. The engine came with a CSR electric water pump and now I'm curious if the wires are reversed and the pump is spinning the wrong way. I can hear the pump cycling however.

Any thoughts??

 

Is it possible someone installed a manual switch for the fans?

Did you verify the fans turn on when you turn on the A/C?

The PCM reads the sensor in the water pump, and that's what you see when you scan.

 

Thank you, Fred...

Only two wires from the CSR EWP is a ground and power, no other wires spliced in.

I have a Davies Craig dual fan switch installed, did that in May. The probe says to place in between the radiator fins, which I've done near the top/left (when standing in front of the engine). Curious if this placement is crap. The neck gets around 190* but the radiator stays stone cold while idling.

 

Is the “fan switch” a device that includes a temp sensor, a control box with relays, and a display to change the temperature setting? If you wired that to control the fans, you apparently completely removed the ability of the PCM to control the fans. That should set a codes for the fan relays in the underhood fuse/relay box. Did you cut the factory wires to the fans and hook them up to the “fan switch”? What advantage did you feel the independent fan switch provided?

Refresh my memory - what year is your car? The fan controls were changed mid-1994 model year. Good idea to add a “signature” so critical info about your car appear at the bottom of every post.

https://www.camaroz28.com/forums/lt1...nature-879835/

 

I purchased the car with the previous owner's missteps which been correcting and this is one of a very few but I feel it's the most important scew up. He originally had two garbage Derale fan switches and they didn't work. I ripped them out and all the wiring that came with them. This allowed me to start fresh with the Davies unit (LED control box, dual relay, 14ga wiring and a temp probe).

The owner ran the yellow trigger to fan fuse #6. But upon looking in the fuse box I see 2 relays for the fans. For the dual Derale fans installed he bypassed the factory fan harness/system for a 12ga hard ground and a 12ga positive feed at the little positive multi-trunk by the battery. I did take note in Data Cat the bit flags for Fan Relay 1/2 switching ON. He essentially removed the factory duty for an "enclosed system" without the PCM controlling the fans.



I had a very partial list of modifications posted in my profile under Message For Visitors since joining.

1995 TA
Golen stroked 383 LT1
D1SC
Dyno Tuned (I have perused the tune with Tuner Cat, touched nothing)
**I can add anything which could be helpful, including a data logged session from last night.

 

And it's the aftermarket controller that's set at 185°F? Sounds like the aftermarket controller is not working.

The PCM only monitors the signal side of the fan relays. If the relays switch when the PCM applies the ground the PCM assumes the fans are running.

I'm surprised you only found 2 fan relays in the underhood box. In late 94 and all 95’s have 3 relays. The relays are wired to turn both fans on low speed (226°F in stock program), and switch both fans to high speed at 235°F (stock). The earlier 2 relay setup simply turns on fan #1, then fan #2.

http://shbox.com/1/fan_schematic_1995.jpg

 

And there's no point in monitoring engine oil temperature, unless the previous owner added an oil temp sensor. The PCM has the capability of monitoring the sensor, but only the Corvette LT1’s included an oil temp sensor. Hence the -33°F shown in you screen shot.

 

Great question- Excellent response!