Light Surge at Steady Cruise
 

I'm just curious what it could be :confused: probably no big deal...(this is in the Integra, BTW)...

It's more of a power draw, then surge.

At highway speeds (60 mph for the sake of discussion), something is cycling on and off that acts like a really weakened version of an A/C compressor kicking-on.

At constant throttle, FE drops very slightly, speed drops, and the feel of a faint "nudge" occurs -- I'm talking hardly noticeable. Then after 30 seconds, another slight bump, the power returns, FE increases and things are back to normal -- that is until it happens maybe 2 minutes later. It happens up hills, down hills -- usually at highway speeds during full TC lockup. No CEL, and the car otherwise operates the same as it always has...

It started about 3 weeks ago. Around the same time as a radiator-block installation. This may have no connection between the 2.

Theories: Since I have no idea, I'll throw out some guesses. Is it the thermostat opening and closing, causing more of a coolant pump load? I don't hear it, but would it be the electrical load of a cooling fan translating back to the alternator->belt->onward? Changes in pressure in the auto-trans / slippage? (let it not be that one...) And yes, the A/C is off :p

Thanks guys...

RH77

Did you not just replace the t-stat? Do you have any other parameters. If it's the cooling fan you should be able to tell by where the water temp is. I've got mine blocked completely and if never comes on in cruise. The highest temp during a climb is 209 and the fan comes on at 211.

The stat was changed over a year ago -- so nothing really recent there. I noticed during the summer that coolant temps would be reported as 216-224F from wherever the sensor is located. The fan would kick-in at 220+, but never went higher than 224. Temps aren't close to that now -- 215 at the most, but 200 at cruise. Lowest ambient has been 15F with freezing rain. On a side note, big time ZR+ tonight -- accumulations up to an inch of ice! :eek:

RH77

Is it possible the cooling fan on high speed could cause enough of a draw that you'd notice the extra engine load? The fact that this started when you added a grille block is a little too coincidental.

One way to tell might be to watch your SG2 voltage parameter. See if it changes when this event happens.

That's what I was thinking but the water temps are 20 degrees below when the fan kicks on. :confused:

I'll monitor the Voltage display during this event. I have noticed that once coolant temps get up to normal, they stay there -- and TC lockup is aggressive (finally) -- even in outdoor temps 10-15F ambient. I also altered the air intake to draw from the engine compartment for Winter. FE hasn't dropped a whole lot, which is a shocker.

Another hypothesis is a knock sensor of sorts, but I don't think it's equipped as such. IATs aren't high enough either.

Honestly, the only inconvenience is a slight drop in power (especially on hills), which has to eat into the FE bottom line. Aside from that, I'm picky about vehicle operation and the slightest abnormalities. :rolleyes: It's so faint, a non-hypermiler may not even notice it unless you monitor the numbers and feel closely for the vehicle's nuances. I just want to better understand the operation. The biggest obvious problem is a leaky valve cover gasket (stinky burning oil underhood) and lack of transmission maintenance. Christmas to New Years = little work in my field, finally! Time for maintenance. And the cold temps are perfect working conditions (better than the heat, IMHO). :)

RH77

Could it be something with the heater operations? Next time it starts doing it turn off the environmentals and see it it continues. Shrug.

It's got me stumped. It's more of an inconvenience or challenge.

The ice wasn't so bad in our part of town, but the airport got quite a bit of ice. We'll see what happens...

At any rate, I'll hook-up the data logger on the Teg to crunch numbers tonight.

RH77

Do you have A/C? It could be coming on as part of the defrost setting. And you'd definitely feel the A/C kicking in.