My H3 Alpha feels like a beast in the morning; 77* ambient temp, A/C off, windows down, engine temp around 1/2, the truck flies (or at least feels like it is flying) on my way to work. I pretty much can keep up and overtake traffic at will. No problem.

Later in the evening, I idle for about 15 minutes in 90* weather waiting to pick up my child from school. Ambient temp at least 90*, engine temp a little over 1/2, A/C on, the truck feels absolutely sluggish when moving off from a standstill. It moves off, but then seems to hold 1st gear too long, with engine revs going up to about 3K or so before abruptly changing to 2nd. It's to the point where vehicles behind me have to switch lanes to avoid me. After changing to 2nd gear, the truck runs a little better, but not as well compared to in the mornings.

If I press the accelerator more, it will sometimes downshift (like a kick down) with the engine racing, but no increase in vehicle speed. If I do this in the mornings, the truck does not unexpectedly kickdown, but instead accelerates forward as expected. It's almost like in the evenings, with the A/C on and increased ambient temperature, the truck loses power, and the transmission wants to stay in the lower gears.

Any suggestions as to the cause of this?

Engine doesn't seem to be overheating, 178K miles, and a tranny cooler.

 

Fan Clutch or A/C clutch

 

Clean airflow restrictions.

 

What you are describing can be completely normal... your PCM is retarding your ignition advance to compensate for heat and changing shift points through the TCM. We would not know that until you scan it while up to full temp so we could look at the actual coolant temp on the scanner instead of the ballpark guesstimate the dash temp gauge provides. Heat compensation by the PCM starts to kick in at around 218-220* F.

A good radiator wash and rinse are an easy starting point.

When was the last time you changed coolant and trans filter/fluid?

 

Hi all, thanks for your replies and suggestions. I don't know when the fluids were last changed, but I need to get them done. I inspected the radiator and it appears the cap is leaking. There was evidence of fluid leak. Called NAPA for a replacement cap, but they no longer carry one for an Alpha; strange. Will have to try another parts store.

I took the cap off the overflow tank and tried blowing through it; I couldn't. Isn't that cap supposed to be open to the atmosphere, allowing air to flow through freely?

Also, is it worth investing in an aluminum radiator, and twin 8" pusher fans in front of the A/C condenser to assist the engine driven fan?

 

All H3s use the same ACDelco RC85 (Part# 15042975) radiator tank caps, readily available through multiple on line sources and any GM dealer.

You would be lucky if it just the cap leaking. Fingers crossed. I would investigate that by opening the hood after you get home on a hot afternoon with the engine running to see if there is a leak or if you can smell antifreeze.

I do not believe the overflow tank is "open to the atmosphere" rather it is just not pressurized like the radiator cooling system. It holds hot expanded coolant until the coolant inside the system looses enough heat (like when it is shut off) and draws it back in for the next cycle.

 

Jmho,
I'd start by purchasing a coolant dye and black light. Poor a bit of dye into radiator and go about your day. Later at dusk hit the underhood radiator area with your black light.
You'll quickly know the area / culprit. Conversely, you could just stop at a local shop and have them pressure test it for you.

 

So I had a friend connect his diagnostic tool to the Alpha today after the check engine light came on, and we got the following codes:
(1) P0056 - O2 sensor, bank 2, sensor 2
(2) P0060
(3) P0328 - NOx sensor
Any advice on what the codes mean and how to tackle the problem causing them?

Crap, we forgot to check the engine temp with the scan tool, but I did order a new radiator cap today as there were signs on the radiator of coolant leakage; will receive the cap tomorrow.

 

you can try looking the codes up on your scanners manufacturers website or you can try this List Of Engine Trouble Codes ? | Engine-Trouble-Code.com

 

P0056&P0060 b2s2 (check wiring & fuse) P0328 Knock sensor (check wiring, any noise from engine, or overheating)