When I first got my 85 Z51 I noticed the main fan operated all the time. So, took it to a vette mechanic and after tracing all the wiring he concluded the problem was in the ECM. He changed out the ECM and added a Hyper Tech Stage 2 chip. Problem solved except the fan now comes on at 175. Next problem: was running hot coolant temps. Same mechanic anylized the problem and he ended up replacing the radiator and added a 165 stat. By the way there was no stat installed when he opened the housing.
Now, heres the question, I am currently running at about 180 in town driving and getting about 14 mpg city and 18mpg mixed. My concern is the engine is not operating at high enough temps and accordingly the carbon build up may cause problems down the road. is my concern justified?
Thanks,
JW

 

Found this info on another forum! Hope it helps!

 

You are running cooler than designed. Car was designed to run around 205-230. What was the temp you considered too hot?

 

Went to the 240's a couple of times.

 

When you were driving or sitting still? Never trust those analog guages, they run about 20deg off I'm told!

 

Sitting, But why take the chance? At that temp you only have about 10 degrees to something bad happening. By the way AF1 I drove a C124.

 

That's cool, I think my Father-in-Law was a loadmaster on them! I was an Air Cargo Specialist, so I flew around in C-130's, C-141's and C-5's. C-130's for the most part!

 

Yea, kind of dates me. Anyway, with those 4 3260CU recips we could run them lean or rich which leads me back to my original concern. Rich caused build up of carbon and nasty things could happen. With my 85 running cool and only getting 14MPG I know there has a consequence. At least thats my thought.

 

Mr Drew...

good assumption.
There is a min temp for the ECM to be "happy" and dialing the inj pulse for optimum efficiency after the o2 sensor gets hot enough to come online and enter CL operation.

Your mpgs are a bit low...it might be time to call Jon. Ohms the inj both hot and cold. Report the findings here or to Jon.
Yours is running rich. Never get past a smog that way..and it will kill the cats early too.

Regarding the temps...230 is near normal. Bad things don;t happen at 250. If they did, I'd be in bad, bad shape. My modded motor with its fortune in upgraded cooling system, hits 235 with ambients of 100, Gulf coast humidity and a/c running at stop lites..
It was worse before I spent a pile of cash on radiators, fans, etc..
My engine ECM makes the "upshift" to CL at 158 degrees on the gauge. I hear the engine settle, smooth out, idle stabilizes. Anywhere below 158 its in OL and the performance is random and subject to change.

Your car probably had the fan rigged to run all the time. Thats old school BS. Running the fan all the time with NO stat is begging for an early rebuild. The car has some "electrical engineering" done to the fan relay or a jumper on or near the ECM...the ECM itself was most likely OK...its been rigged for fans to run at Key-ON. There are lots of ways the bubbas do this. Jumper wires, shorting relays..rarely done right in the prom.
Oil that never boils is oil thats FULL of moisture and crud. It likes to be HOT. It was designed that way and these engines go for 250,000 miles easily when the oil is changed and its taken care of...running at factory temps.

Fans coming on at 175 is kinda pointless...they'll come on and end up staying on. You need the following ...

195 stat. (remember, the stat controls the miminum temp ONLY, past that the stat is worthless) You want to control the MAX operating temps...not the min.
I might use a 180 in summer since my fans run at 185) Factory fans WAS 226 on all L98 C4s..

Get a program for the prom fans ON @ 185-200. (ECM turns 'em off at speed and a/c turns 'em on with air)
Keep the Air dam in GOOD shape. This is ALL about air flow...potential heat exchange.Clean between the condensor and radiator. Take the top shroud OFF. No other way. Its easy and worth it.

Your car likes 30-35 mph. Thats moving more air thru the rad than the fan can. That fan is more for back-up only. Its made to come on when sitting still and turn off once moving again. The system is more complex than just on/off..and when. Lots of things going on here.

Before your shop guesses about anything else, spend the money on a REAL FSM. You can get used sets on fleabay for $75. The books are worth their weight in gold..and they will describe exactly what is correct and why.
Until then get the 195 stat since its winter, and get a prom thats not going to waste fan time...its pointless for fans to run if hot water is not circulating..stat and fans should come on somewhat together. A fan that runs before the stat opens is cooling cold water.

Bottom line...
Normal operating temps are: 185 to 225. In extreme climates...240. You don;t want to run colder than 175 for extended periods. Certainly not under 160. Oils not even warm at that temp.

MPG...good would be 27-28 hiway, 17 city,. 19/23 combined. Jon will help. A 1985 L98...I can assure you that its time to see Jon. Everything will get better when you do.

 

any idea what your A/F ratios are? It really sounds like the car is running pig rich, which is causing heat, which is causing the fan to come on....

perhaps the hypertech chip masked a faulty MAF (or MAS - can't remember the year they changed) sensor reading...