My main fan comes on at 228* and is off around 214. I grounded the pusher fan in front of the radiator (aux. fan). It came on, my guess is, for the first time in its life. By the way, the pancake motor in front of the radiator is a much better motor than is on the main fan. Double ball bearing etc. and I know a way to get 1250 cfm out of it. However, one has to ask. would it be better just to take it out? As in my oppinion it is an emergency fan, and it BLOCKS airflow to the radiator. So even though it is a great fan, that doesn't run. Is it just a big blob of debris in front of your radiator? I've been studing this intensely. I'm not 100% sure the temp. the aux comes on. Does it matter? I have a heavy duty radiator that I cleaned, and straightened the fins, as I had a huge amount of debris in front of it. It took me days, as I am a perfectionist. Then it was on to the condenser. After all what good is a nice clean radiator, if it can't get air? so I spent days on it, and it was harder, because I had to do it in the car. I've got it about 90% there, and that was the best I could achieve. It is buttoned up now, and I will report when I get it back to together, the outcome. I need to PM Lord Vadar, with a question. I might be able to make things alot better for C4 vette owners. Thanks...

 

Check your dash gage then with a scan. You can rule out resistance in the signal by disconnecting it - gage should peg LO. Grounding it should display 300. Otherwise, you usually see no more than a 75 degree temp diff between the radiator and the condensor putting your head pressures close to 300. The system can handle it, but your vent will be in upper 50's. Hopefully, you pulled a vacuum until all the moisture was out of it.

 

I never stated that both fans come on at 228. In my very first post I stated that the Aux. fan comes on at 228 and the main fan at 226. This is per factory spec. Where did you get that I said both fans came on at 228?

Well now, I did not know that the 86 manual clearly stated that the main fan for ALL YEARS comes on at 228. Amazing how they knew in advance that the 87 - 96 C4s would never change the cooling system. Funny, I was under the impression that the cooling systems did change quite a bit in later year C4s. I guess that in 86 they knew that a the LT1/LT4 would not really need a different radiator, or have to meet stricter emissions laws, and therefore would require no fan temp changes. The LT1 and LT4 guys can probably save big money by using L-98 radiators, hoses, and thermostats. Heck, they can use the 86 manual too, since it's cheaper and as you say, there is "... no a priori reason to assume they would change it.".


According to your words there are 3 different temps quoted, but only one is correct for the fans. If there are 2 fans and only one correct temp in the 86 manual, aren't you saying that ONE temp is correct for both? In other words, they BOTH come on at 238? Do you see how your post is misleading?


I try never to give 88 model year value specific advice to owners of other year Vettes as if it applied directly to their year unless I know it does. The 86-89 EGR temp switch looks exactly like the 85 switch, works like the later switch, and the ends are exactly the same. An 85 switch can even be used on an 88. Does that mean I should tell an 85 owner he can buy one for an 88 to use on his 85? NO. The 85 switch is approx 8" longer and needs to be. An 88 switch cannot be used on an 85 without modification. Should I recommend that a 90 L-98 owner check his cold start injector circuit when he experiences hard starting because it worked for me and others with 85-88 L-98s? NO. No such injector on the 89 - 98 L-98. If you have a 86 4+3 does it go into OD at the same temps as my 4+3? NO. So, "...theres no a priori reason to assume they would change it." is just wrong.


Well, the reason you picked to disagree with the factory service manuals might be blatently obvious to you, but it isn't to everyone else. In addition, the methodology you used may be accurate or it may be suspect. How did you come to your conclusion? Did you use a calibrated thermometer or other known accurate instrument? If you used the reading on the 86 digital dash as a guide, there are a couple of ways you could have made an error. The digital dash temp sensor could be out of spec due to age. The Aux fan switch could be out of spec and while that may cause the aux. fan to delay coming on until 238 on your Vette, that doesn't mean the manual is wrong. What did you use to verify the your value is correct?

I don't dispute that there are errors in the FSMs. You and all of us have good reason to question the accuracy of any value in the manuals. That is what makes this forum such a valuable resource. Before you quote non-factory specs for an 86 to someone with an 88, it might be a good idea to say what method you used to decide that the manual is incorrect and that the 86 values apply to an 88.


Steel Breeze, you do realize that the digital dash reading is not coming from the same coolant temp sensor as the ECM? A difference of 2*F between sensors is not unusual.

 

Of course, a 100% accurate gauge is almost unheard of. What I should have said, is it comes on around 228*. I've seen 227*, even 231*, but it is usually right as the gauge reaches 228*. Then it climbs to 232* to 236* before it comes down. Which is of course, thermal Inertia. Ya, I do no there is a sender for the gauge, and one for the ECU existing as seperate units. There is also the aux fan sender that is seperate from the above mentioned. It's really not that complicated, Being an electronics tech. That is why I am working on a project for this C4 temp. dilemma. In my oppinion they run to hot. They run hot for emmision purposes. Imagine what the alternator is going through, bearings, wiring, intake, fuel rails, belt, brake fluid, and on, and on. I was wearing the brushes in when I rebuilt my windshield wiper motor. Within 15 minutes, the motor was so hot, I couldn't touch it. Imagine how hot it gets when running in under hood temps. I hope the underhood bearing, and bushing oils are VERY high temp. I say fans on at 205*, and off at 190*, and that is plenty warm, but logical...

 

I agree. I bought a new aux. fan switch from MidAmerica that does exactly that. Turns the aux. fan on at 205 and off at 190. Easy plug and play swap. I spoke to Gordon Killebrew last Sept. about this and he recommended splicing the wire that goes into the aux. fan switch into the main fan relay circuit so that it turned on both fans at the same time, rather than have the ECM wait for 226* to turn on the main fan. On the 88, the main fan relay is on the driver's side pretty close to the aux. fan switch location, so it would be a fairly simple mod. On some of the earlier C4s with an aux fan, the switch is on the passenger side, so it may be doable, but not as convienent.

 

That's exactly how mine is wired..like Gordon recommended, and I'm as pleased as punch..well, actually, both fans come on at 200 and off at 185. This is on my 87 BTW.

 

I've contemplated that. Flip both fans on, and off at the same temp. They should have wired it that way. However I believe they were kinda watching out for the current draw. The fans wouldn't stay on as long. So in my oppinion, it is as broad as it is long. kind of a catch 22 situation. Gordon know's his stuff...