2000 with 143K...

Summer sympton...hot weather only.

Overheats and sputters badly then dies going up steep hills at altitude (>7K ft.). first symptom is zero power(the more psuh the excellerator the faster it will die.), then temp rise to 240....pull over 20 minutes and OK for a bit...almost like vapor lock. But the oil was smoking from the fill cap.


But this time, it repeated once I was down the hill in my neighborhood. No obvious leaks, no coolant loss (nice clean fluid), fan (and clutch) seems to work fine, upper radiator hose soft at temp. Oil pressure good, heater good, a/c good.

Just can't trust it to get up the mountain.

Any ideas?

 

Does the SES light come on? If so what DTC's are present?

Lean fuel mixture will cause it to run hot AND lose power. Fuel mixture normally leans out at higher elevation but if the fuel filter is restricted or fuel pressure is low, it will make the fuel mixture even leaner. Fuel pressure is not directly monitored by the PCM so it can't turn the SES light on. Check fuel pressure and leakdown: Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off.

A soft upper radiator hose at operating temp could be caused by a faulty radiator cap, or an air bubble in the cooling system, which can also cause it to overheat due to insufficient pressure. Could also be a faulty thermostat.

 

No SES light.Has new fuel filter, and thermostat did fuel pressure, leakdown and fuel volume test, all good. Thought soft upper radiator hose was 'good' (hard would indicate plugged radiator. Air may be possible, we burped it with a regular funnel as best we could.

Has aftermarket radiator after 2" body lift, and fluid id beatiful, so should be OK. As the matter of fact, we had to put a 190 deg. thermostat in, because it was running too cool last winter (heat would not get hot).

Changing the radiator cap is a good idea.

We have a front bra that has a full screen in front of the radiator opening...could that be an issue?

Anyway, we took it off.

We have always had a power and hard shift issue, (many older posts). But it runs like a top as long as you keep it out of the mountains. We were going to sell, but decided to keep, (It's my son's car), so here we are again, drying to find the secret problem.

 

the temp thing sounds like u have covered. the altitude is an east fix, nothings wrong most likely. when u turn key on just before it starts, ecm takes a reading of the barometric pressure(by the map sensor). onece ur running the MAP sensor now reads engine vacume instead. its normal at changing elevations to have to stop,power off for 30 seconds and continue on until elevation requires it again, the heights will change and make it leaner or richer depending on conditions. that sensor is rare to fail, its in the plastic upper plenum on the pass, side i THINK, maybe other side, behind the throttle body. Its small, black, 3 wires run horizontally. unplug gently hold 2 retaining tabs back and pull sensor out. just a rubber o-ring thingy on it. look at its nipple, these do get plugged with carbon goo and will be lazy when load is applied. dont stick anything far or solvent in there u will hurt it.

Duralast/MAP Sensor (SU1078) | 2001 Chevrolet Blazer 4WD 6 Cylinders W 4.3L SFI | AutoZone.com

 

oh and these things are always on the edge temp wise under load. hose the radiator and condenser out bolth ways till clean, use a bottle of red line water wetter, good stuff will take some heat off. no bra if it restricts it, take top fan shroud off, look between rad an condensor all the way down, u may have a blanket of fuzzy stuff in the front of radiator u cant see. n if u got her that hot u better change the oil, its ruined over 230. all this will only take an hour to clean, DO IT!

 

Looking for actual numbers here...
What is the fuel pressure and how long does it hold above 55psi after the pump shuts off?

Thermostat needs to be 195 degrees, year round. Soft hose indicates that pressure is not building up in the cooling system: either a leak, low coolant level or a faulty radiator cap. The radiator cap is what regulates cooling system pressure: At normal operating temp, it should be ~16psi, (hard hoses). Pressurizing the cooling system increases the boiling point. The "bra" is obstructing air flow, no question about it.

Fan clutch:
On a cold start up, the cooling fan should "roar" for a few seconds, usually anywhere from 5 to 20 seconds depending on how cold the clutch is. Colder ambient temperatures cause the fan to "roar" longer. The "roar" should gradually decrease as the engine warms up. At normal engine operating temperature, the fan should not "roar". When/if it overheats, the fan should "roar" to pull more air through the radiator. The fan clutch is an often overlooked, necessary part of the cooling system. They fail more often than most people realize.

 

Hey guys, really appreciate it...here's what we did today...

Put a bottle of seafoam in the brake booster line, just for fun, since we were going to change the oil.

Looked at the MAP sensor, it was dirty, but not completely clogged. Decided to clean with Mass Air Flow cleaner, as the part was $53.00, otherwise, it was not cracked, and looked fine.

Replaced oil and filter.

Looked around radiator, condensor, oil cooler, etc....clean as a whistle. The coolant looks brand new, I can see way into the radiator...cooling fins are as clean as new.

We could not find a new radiator cap as it was an aftermarket brand, but the main seal was good. It was a 15lb cap.

Fuel pressure is right at 60-61 and holds above 55.

Fan clutch seems to work well, it's usually on when it needs to be, but we did not push it today, will have to check that next time we head uphill.

Weird thing is that is still shifts a little late and very hard....and seems to put all it's energy into the shift, and it needs a brief rest after the shift. 2nd hits the hardest, but the lag is worst after third. Just can't get any power in 3rd, even a slight uphill run in third requires a downshift the 2nd. We stopped short of replacing the spider, and the distributer mechanism.

Won't know more till we head uphill...

 

Can't tell if the cap is good just by looking at it. For the amount of fooling around involved with testing it, it's hardly worth it. For $5 you can put a new one on.

Have you checked for an exhaust restriction?

 

We tried Napa, Autozone, and O'Reilly, no caps would fit. The wording on the cap is gone, except the 15lbs.

Exhaust restriction has been checked thoroughly. We have a free flow system with the CAT removed.

 

well w the trans too the map is involved in making power under load, u could have a maf going or tourqe converter. sounds like you need to find a honest independent shop around to diag it for u, a god tech w scan tool and a vac gauge should be able to find it right off, driveability can be difficult so stop around and see whats around for techs. it may save some aggravation and engine life.