[Hostile_1LE]

Hey all, I'm just wondering if it is normal for the radiator fan to come on after a decent pull at WOT. I noticed that vacuum leaks cause the fan to come on. I learned that when installed my roto-fab and forgot to connect the factory air-oil separator, the fan wouldn't shut off, but when I reconnected it the fan would shut off shortly after. So now anytime my fan comes one (when the AC isn't running) I get a little worried. It don't remember my fan ever coming on prior to. My worry is that my MSD intake is leaking or something to that extent. Car doesn't feel down on power from what I can tell, and there are no Code related to the engine at all. Coolant temps never go above 205 or so. It could all just be in my head, but I'd love to get some thoughts on the matter. Curious as to what vacuum leak symptoms are on these cars and possibly how to test for them. My tuner said he didn't notice any leaks when it got tuned a 1000 miles ago or so.

TLDR:
Radiator fan comes on after WOT pull even though coolant temp stays below 210 and there are no codes related to the engine.

[SnakeEyeSS]

Heat is my guess.
You are in Texas, here is OK it's been over 100 quite a bit lately. The fan is supposed to prevent overheating, not wait for it.

Is it coming on ONLY after WOT?

[Hostile_1LE]

It's too difficult to tell. the car is too loud to hear anything else during WOT and most of the time the wind overpowers the fan sound. It was just something I heard once. I checked my fuel trims and they seem to be all over the place. Like anywhere between -15 and 15 % when I went on a drive. That is from my little obd2 app though, so who knows how accurate it is. Wouldn't 15% trim indicate a vacuum leak? Running 75-ish percent Ethanol right now.

[Hostile_1LE]

Actually, I was reading the fuel trims wrong. I wasn't maintaining a constant RPM. I'm not sure how accurate CarScanner for IOS is but I used it to log my trims at different RPM's. I'm sure something like HPtuners is better, but this is all I've got.

Idle:


2500 RPM:


3500 RPM:


If someone could tell me if these fuel trims indicate a vacuum leak, please do. Didn't include LTFT's because they were both 0.

[ctrlz]

Originally Posted by Hostile_1LE

TLDR:
Radiator fan comes on after WOT pull even though coolant temp stays below 210 and there are no codes related to the engine.

Well, at least this made me look up "tldr"!

Anyway, I think this may be related to HVAC. Radiator fan module responds to coolant temp and IAT. But ECM (or BCM) also shuts down A/C compressor at WOT. Once WOT is over and compressor turns back on, it may default to 100% duty cycle for the radiator fan, at least for a bit. These subtleties often go unmentioned in the repair manual.

[Hostile_1LE]

I would agree normally, but I did all my testing with AC off

[Hostile_1LE]

I've also realized that fuel trims may not be the best way for me to find a leak, as there are too many factors that can make trims increase. I have a very small exhaust leak behind the transmission and my cars has 32000 miles without any sort of fuel system cleaner, so that could account for a small amount of trim.

[Kamero6]

I don't know if it is still a thing with GM, but 90's corvettes will blow the fan at full speed if any fault is present. Some of them don't have to trigger the CEL.