Chevy Cobalt Forum banner
1 - 18 of 18 Posts

·
Registered
Joined
·
1,080 Posts
Discussion Starter · #1 · (Edited)
Hey this is a puzzle. The BC is running great getting 35-38mpg on hiway 1/2-3/4 tank runs. Just last night, ran from OKC to Dallas @ ave speed of 71mph @34.9 mpg. Filled up today and got a 5qt jug of 5W-30 Mobile 1 and a new Fram filter. Drained the oil & installed the drain bolt. And started filling the engine with the fresh oil into a funnel…don’t want to dirty this ~10,000 mile engine and splashed about 1/4 cup of oil between the cylinder head and fuse block….well Pooo!….oh well it’s time for a dusting off bath any way. So completed the oil fill and checked the dip stick. Ok let’s fire it up before I splash the engine with some water…….
Nope. No crank….LOW FUEL…no crank, clutch peddle all the way down…low fuel..
well phifff,!!! Check voltage, 12.57V under hood, 12.65 at the battery…no start..low fuel
Frustrated, I rinsed the engine and all is well??? Engine starts without a problem.
This will come back to bite me sooner or later.

For those interested, the BC is an 08 LS 5 speed with a new, 10,000 mile engine with a Feb 08 build date on the engine. Full FE5 suspension, leather Steering wheel with fully functional cruise and radio controls,

@Oldslowandugly, @MP81
 

·
Registered
Joined
·
1,080 Posts
Discussion Starter · #3 ·
Now that the brake booster and master cylinder was replaced again with right at 10k miles on the new engine. I get the famous —-F and no AC and the nominal P28xx code. Zeroed the code, ac is back temp reading a bit low and the engine is warming up slowly…..l
Ok most likely the T-stat is blocked open. $16 later for a new Stant 180F, …the 1 yr old t-stat and gasket/o-ring looks perfect. Popped the new one in anyway and refilled the coolant system with Pink GM flavored juice. Better, but still slow warm up.
With AC off sitting at idle for 5 min engine temp up to 190F…good. But what the!?
Now this was in a new t-stat housing with new hoses and new temp sending unit. About to go over to the original engine and borrow a few parts.


Thinking poor connection between temp sensor and ECM is possible but the warm up rate just not cutting it.
At 75F, I should be up to temp in 6 blocks on normal driving and 190-200 within a mile at 55-65mph
@MP81, @Oldslowandugly
Suggestions!
Luckily, I had just passed state emissions on1sep2022 w all IM codes ready except for evap,
 

·
Registered
Joined
·
309 Posts
Well you had the entire engine out and everything disconnected so....... what could go wrong? Just kidding. Loose ground, oil on fuses, lots of things to check. I changed a thermostat at around 50k and it made no difference at all, it still runs hot. When you did the swap were you doing it in your spare time with no pressure or you needed it for work the next day? I ask because LOTS of stuff gets done wrong or not at all when in a hurry. As you said, good thing it passed already. My luck is a code the day before the inspection is due.
 

·
Registered
Joined
·
1,080 Posts
Discussion Starter · #5 ·
Thanks OSU….no all of the time was focused on the problem at hand and trying to stay cool. And yes, I just ripped everything electrical in the engine compartment when I completely removed the fuse block to access the brake booster. Yet, I think the engine temp sensor runs directly to the .ECU….those connections were not messed with….maybe they should. But the warmup rate leads me to think I have a 160F tstat
 

·
Registered
Joined
·
1,080 Posts
Discussion Starter · #6 ·
Now remember….10k trouble free miles then ac compressor went….full system replaced. Then brake booster….ripping out the fuse block then had left headlight…loose connector in fuse block…now slow warm up….,,
I touched something…..what?
Need schematic to 07-08 ECU & sensors to prove….for 2.0l T Malibu…t-sensor goes directly to ECU #5….. might need to open & close connectors a few times and grease
 

·
Registered
Joined
·
1,080 Posts
Discussion Starter · #8 ·
@Oldslowandugly
Always interested others will be too, it would be nice to see that the engine coolant sensor connects straight to the ECU…expecting the connection on about pin2
I heard from Coby7 and he offered “ambient temperature sensor in the grill”. This might be for an outside temp reading.
So while there is still light, I’ll take the t-stat from the original engine and the 10k mile tstat and hot water test them on the stove with a good digital thermometer.
OSU if you had the engine wiring harness schematic that would be super cool. I can’t seem to pull mine out
 

·
Registered
Joined
·
309 Posts
OK, for a 2008 2.0 the wires from the ECT go to the ECM at connector X1 at terminals #82 [yellow-reference voltage] and #44 [tan-ground]. Why can't I get the scanned page to post?!? All I can do is this and it won't rotate. Maybe this way?
Rectangle Slope Parallel Font Number
 

Attachments

·
Registered
Joined
·
1,080 Posts
Discussion Starter · #11 ·
Cool Thanks OSU that’s the schematic I was looking for…..Simple yes?
It confirms my suspicions that the engine temp sensor goes directly to the ECU.
Remember, the last repair was the brake booster. This necessitated completely removing the fuse block. For the ECU, I simply unhooked it from the fuse block ??? Bracket and laid it aside out of the way without disconnecting any of it connectors.
Now today, all is fine with the world…WT.??
It’s 84F outside. Outside BC air temp 84F…Coolant temp 84F. Seems they all agree. Started and drove 1 block, coolant temp passing 100F…drove 3-4more blocks toward hiway temp now 155-160…
Looking good.. onto the on-ramp to 55MPH. Temp up to180-181 now 1-1/2 to 1/3/4 miles and all is fine. Turn AC on coolant temp drops to 179. Then back to 181…..heading home. Hi temp about 183.
AC giving freezing air..feels good.
I can’t figure. I did reach down and just touched the temp sending unit before I started the drive.
No Idea what but it seems to be working……just one of those Cobalt things I guess.
 

·
Registered
Joined
·
309 Posts
That's the problem- you "touched" it. You know how those things happen. I'm glad it's working because the FSM indicated things like low coolant, bad thermostat, bad sensor, bad ECM, debris blockage, all sorts of fun things to cause low engine temps. I never have that problem. It's always overheating.
 

·
Registered
Joined
·
1,080 Posts
Discussion Starter · #14 ·
Yes I had to mention …I touched it.
You should have seen the new thermostat housing and eng temp sensor, new in the box and installed on the engine. Problem free until after the brake booster…..must have wiggled a wire somewhere. Now if it returns, it will be a methodical, connector by connector remove, clean, coat with dielectric grease, & reassemble. I did the easy job of replacing the thermostat for $20
The nice thing now is we are over the week after week of +100F temps outside. Nice 72-78F overnight till 10ish
 

·
Registered
Joined
·
309 Posts
Yes, I too have a mountain of work I postponed because of the oven being on all Summer. I need to do the rear leaf springs in my Jeep as well as other headaches. And of course now that Fall is looming the fish are biting and that eats up a lot of my time.
 
1 - 18 of 18 Posts
Top