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Still running cold?

dhcomp

dhcomp

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UPDATE, see below


Ok, so what are the symptoms of a cat going out on a 94 blazer? 350tbi, 173K on teh ticker.

Something is rattling at low rpm's, and when i slam the passenger door. I can't find what it is, but it think its coming from the cat. Rattles at idle when cold, and sometimes when warm. Is my cat coming apart? If so, any reason to get a hi-po cat as a replacement, or are the OE just as good/cheap?

Also, i noticed recently that my truck has been running cold. When warmed up in town, it will reach 200˚ (one tick from marked 210), then drop back down to 180-190. It ALWAYS run around 200˚, hot weather, cold weather, under load, on freeway, whatever. So it worries me it is changing. It also seems to heat up slowly...... Tstat is recent, as is waterpump (both 6-8 months old).

Any idea what would cause this?

This truck is my DD, and NEVER lets me down, so i want to figure out these problems before they get bigger and leave me stranded.

THanks guys!
 
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I have heard the the exhaust will smell like sulphur when a cat is on its way out. If it is the cat that is rattling, then some of the cat internals may have rusted (or burned) out. Fire it up cold and crawl under to listen.

T-stat stuck open?

Long shot: Bad O2 sensor causing it to run rich, would cool it down and kill the cat more quickly.

Sorry, thats all I got.
 
hm, ok. I just had a smog done, so I'm tempted to cut the cat off, dump out the loose $hit, and put it back in for the time being. Or maybe gut it completely.......but probably not.

Tstat might be stuck open, but i doubt that would cause it to run cold once up to operating temp....it would just cause it to heat up slower.
 
If it passed smog it's probly not running rich enough to kill the cat.

Cut it off and blow it out- if it looks bad look for a replacement from a junk yard.

Fan clutch stuck engaged?
 
You can check for plugged exhaust by watching engine vacuum under varying RPM's.

I just glanced at the GM test in the manual the other day, something about idle vacuum, compared to what it is at 2500RPM.
 
The cat that you have is most likely the pellet type and they will rattle. The one on my 92 did if from the day it was new. I would replace it with one of the newer honeycomb types. The new type will flow better and be a lot smaller.
 
ok, sounds good. How would i check for a bad fan clutch?

When does the fan run? And how would i tell if its running while on the freeway?

Obviously, it runs when the motor is warm around town, but above those speeds, i doubt i would hear it......
 
As I understand it the fan clutch allow slip at higher engine speeds but is pretty well locked at low engine speeds. Usually when they fail they slip too much. You could try holding the water pump pulley still and trying to rotate the fan by hand (with the engine off, of course). Make sure that the pulley isn't moving, cause the belt may not hold it. They best way to check would be to compare how it feels with a truck that has a known good fan clutch.
 
The cat that you have is most likely the pellet type and they will rattle. The one on my 92 did if from the day it was new. I would replace it with one of the newer honeycomb types. The new type will flow better and be a lot smaller.
Click to expand...

94 should be monolithic, my pickup's is. aftermarket i have a magnflow universal fit monolithic on my k5 and the truck runs better now than it did with the PO's gutted pellet-style cat. easiest way to check for a clogged cat (which it does not sound like you have) is to drill a hole before the cat and one after, start the engine and then feel, gauge, or see (use some sand, water, etc, below it) if there is a significant difference in pressure. in all cases, the hole before should have slightly higher pressure, even on a high-flow cat, but if the difference is significant, you probably have a clogged one. if you want a quick check, lay under the truck and hit the (cool) cat with your hand. if a pellet-style doesn't rattle, it's gunked up or melted down. if a monolithic does rattle, the catalyst brick is broken.
 
vortec said:
94 should be monolithic, my pickup's is.
if a monolithic does rattle, the catalyst brick is broken.
Click to expand...

Thats what i am guessing is going on. Now to check if its bolted or welded on....and proceed from there. If its welded, ill prolly have a shop replace it, as i don't have a mig welder, and can't stick weld well enough to do it myself. Thanks!
 
On the fan clutch, when its cold if you can hit it and it spins pretty easily then its probably no good. There should be some resistance. When the engine has been ran a while and its warm, the fan shouldnt spin much at all and there should be more resistance. You shouldnt have to hold the pulley still, if the belt wont hold it then something is else wrong. I wouldnt recommend gutting the cat and putting it back in, I did that in my old truck and it was cool for a bout a day, it resonated horribly. This summer I thought my engine was overheating according to my gauge so I pulled the radiator and flushed it, put a new water pump in, new t-stat, a brand new "severe duty" fan cluth off a 454 (it basically doesnt slip lol) and even a new cap. Long story short, my gauge is messed up so I am weary of the factory gauge....I wouldnt put it past it. You might try flushing the radiator is you havent, easy and cheap.
 
What degree tstat did you put in?
Stock is 195* But if you put in a 180* Tstat it shoud run between 180-190.
Also as said you cant always trust the stock guage. Mine is off about 5* from what the ECM sees.

There 2 types of fan clutches. Thermal and Non thermal.

Non thermal dont have a coiled spring in the front. They are, and should be fully engaged at low speed. At high speeds the silicone fluid contained in the clutch will lose its ability to transfer the energy from the shaft to the fan clutch body (and therefore the fan) and the fan is then allowed to almost free-wheel, removing its load from the engine.

Thermal fan clutches have a coiled spring in the front of them. They freewheel all the time. Untill heat from the radiator causes the bi metal spring to expand and contract. Engaging the fan when the radiator water is hot, and shutting it off when the radiator water cools down.

You need to id what kind of fan clutch you have before testing them as people have told you above.
 
When I bought my 96 it's cat was toasted. I paid 150 bucks to have a new one installed and the rattling went right away :)
 
my bad I didnt even think about it possibly being a non thermal clutch. Did gm ever put non thermal clutches on theses trucks, blazers, etc.? I always assumed they were all thermal (hijack off).Even if it is thermal there should still be some resistance when cold.
 
ok, so i replaced the thermostat, lets see if that does anything. It got dark and i didn't get to check the fan clutch, but there is some resistance to spin it when cold.

I also lucked out, and the cat is bolted on. Got it unbolted, but ran out of time to screw with it an actually get it to come out, not much room to play to get the flange to slide out. Either way, should have the cat out tmr, and get to look inside.

and probably drive it around the block with open exhaust :haha:
 
Sounds like the cat might be getting ready to clog. My buddy's Jeep rattled like that for like 2 months, and we never could figure out why. Then one day it just died on the freeway, and never would start backup. Clogged cat.
 
Ok, so i unbolted the cat, but didnt' have enough room to slide it out. THere was piece of pipe welded to it, which bolted to a flange about 8" from the cat, but there wasn't enough room to slide it apart. I tried to loosen the rest of the exhaust system and slide it back, but someone at midas tack'd the nuts on the rear exhaust hangers :mad:.

So i broke out the sawzall, and cut it in the straight section. Removed cat, to find it 80% broken inside, and rattling. I had to break like 2 pieces, and it all just dumped out :haha:. So i didn't gut it, cause that would be illegal. I just poked at it in a couple places, then accidently set it open end up. Some stuff fell out, but i'm not sure what it was ;), so whatever, i decided to put it back on :wink1:. Didnt' feel like buying a new one, ill deal with it when smog comes up in 2 yrs.

So when i was removing it, i hit it with a sledge on the little bungs that are welded to teh side, and tore the casing a little bit. I bent it back close to sealed, and broke out the welder. Problem is, i don't have a mig, and suck at arc welding. Decided that all i had to lose was an empty cat, so i welded it up with the stick welder. I suck at welding, not much experience, but i got it to seal up. I was sorta proud of myself (but not proud enough to post pics :haha:), so i decided to weld up the part of the pipe that i cut. Figured a coupler and clamps wouldn't work too well on old a$$ rusted pipe anyways. So i booger welded it back together. Checked all the sections i welded with a shop light, and no light shined through, so i guess i sealed it up ok. If i'm able to access a mig soon, ill grind it off, and weld it properly, but for now, it gets the job done. Ghetto, yes. Cheap, yes. Functional, totally.

Fire up the truck, no more cat rattle :D. And exhaust note is a little deeper and louder than before....works for me.

Haven't driven the truck really since the new tstat, but i think its still not heating up. I'm gonna put some miles on it tmr, and see what happens. THanks for your help guys!
 
Ok, so i replaced the temp gauge sender, and the truck is still running cold.

Drove it 50 miles or so today on the freeway, with teh temp gauge at like 1/4, when it normally rides right at the 210 mark.

What would cause this? I'm watching it closely to make sure its not burning coolant, and dreading some sort of head gasket leak......

What else would cause it to run cold on the freeway?
 
Dumb question, are you running an HEI dist. The wing weights will weld in place and the timing advance doesnt work. Dont rebuild it with cheap aftermarket kit. GM only parts for these to be dependable.
 
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