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overheating?

pblaze725 said:
I looked up an '87 TBI at my local parts store and it shows 160*, 180*, and 195* but not the 220*. (CLICKY)

Maybe you have the wrong thermostat in there.:dunno: IMHO I would use the one that opens the fastest.
Click to expand...
The TBI trucks SHOULD use the 195 (or thereabouts, my 91 uses a 195) thermostat. Without getting over 200 degrees, the engine never reaches peak operating temps and the TBI system works very, very poorly.

210-230 is the operating temp you want (I think) for the TBI Chevy 350.

Edit: Here's my research from before about the thermostat: http://coloradok5.com/forums/showpost.php?p=2893965&postcount=14
 
I'm using a Napa Premium thermostat at 195. The one that my mechanic put in tested good, but I figured they're cheap so I'd put a good one in. I never skimp on the thermostats since this truck seems to like to eat them every couple years. I forgot this round and it bit me.

I plan on driving my truck around for a few days and see what happens. Hopefully the overheating doesn't come back.
 
Jessie James said:
The TBI trucks SHOULD use the 195 (or thereabouts, my 91 uses a 195) thermostat. Without getting over 200 degrees, the engine never reaches peak operating temps and the TBI system works very, very poorly.

210-230 is the operating temp you want (I think) for the TBI Chevy 350.

Edit: Here's my research from before about the thermostat: http://coloradok5.com/forums/showpost.php?p=2893965&postcount=14
Click to expand...

I dunno, I think 220 on up is on the warm side.

I have a 4 core radiator, heavy duty fan clutch and the stock 195* t-stat, it runs right around that t-stat level here in the Arizona weather, usually right around 200 and it does just fine.

The '05 Avalanche here with the 5.3 runs at a constant 195-200 with the factory electric fan setup as well.

I've always seemed to notice that when they get up towards the 220 range, they usually start going up higher, pretty quickly unless something is done like slowing down, or water over the radiator to help cool it down. But then again, if the system can't maintain a steady temp, then there is probably something not totally correct with it.
 
My 87 with 350 with a 195* thermostat runs right at 195*. It will go up to about 200* and the thermostat opens and it drops back.

I'm sure your head is spinning with all the info thrown out on the table. I think you are being wise to just drive it a few days and observe.
Think about it a little. IF it really was getting to 260* you would have had coolant loss and a lot of steaming and possible busted hoses. You took temps and even when the gauge showed 260* you could only find 200*.
 
I've been driving it around for about a week now and it seems to be running okay. A few times it's gone a little too high, but comes back down (that only happened when it was near 100 outside). I also think this may be because the new temperature sender is being more accurate than the old one which would sit around 160-210! Even so, I'm probably going to replace the water pump and lower radiator hose sometime in the next month or two since I realized how many miles the pump has on it (maybe radiator too, just so I can say I have a new cooling system!).

For posterity, I figured a summary of everything I've done to try and fix the overheating is in order:
1. Mechanic replaced the thermostat and temperature sender.
2. I got a new gauge, which displayed the same information as the old one. I proceeded to do the 90-ohm gauge test. Everything came back okay except both gauges read half-way when grounded with 90 ohms instead of max. I still don't know what the deal was with that. I put the original back in and it's working fine now (well, after step 3 below).
3. Tried a cooling system pressure test, but ended up pushing coolant out the thermostat gasket at some point after I put it at 20 psi. It held for 5 minutes after I pressurized it and then I left it for three hours, but still inconclusive.
4. Radiator cap was replaced since the old one wasn't holding pressure with the cooling system pressure tester. I'm not sure if this wasn't it just not sealing on the pump's adapter though. I should have tested the new one, but it didn't occur to me.
5. I noticed burbling noises in the heater core and could feel bubbles in the upper radiator hose when running. So, I purged air that was in the cooling system by running the truck with the radiator cap off until it got warm and puked a third of the radiator out. This immediately brought the temperature down to reasonable levels.
6. Since there obviously was air in the system, I needed to rule out a head gasket. I did a compression test which came back with every cylinder reading almost exactly 145 psi cold (I tested it warm, but forgot to open the throttle and got 120 each). So, no head gasket issues.
7. Verified the thermostat was good by boiling it on the stove. It was.
8. Purged the cooling system of air again after draining it for the thermostat.

I've probably done too many things to know exactly what was the issue, but I think it was probably a combination of gauge issues (which got fixed some point when I had it all apart), radiator cap, and air in the system. The last outstanding mystery is why air wasn't/isn't being purged out through the overflow tank. I think the next thermostat I get, I'm going to drill a small hole in to let the air through.

Thanks everyone for your help! :bow:
 
There is no need to drill a hole in your thermostat. If there were, I am sure the auto manufacturers would have done it. Remember, the designers are guys who have engineering degrees and spend thousands (if not millions of hours now) working on engine technology. No one drills a hole in their thermostat, and there is probably a good reason.
 
joshkbomb said:
The last outstanding mystery is why air wasn't/isn't being purged out through the overflow tank. I think the next thermostat I get, I'm going to drill a small hole in to let the air through.

Thanks everyone for your help! :bow:
Click to expand...

And as for the post that follows. Most thermostats you buy now, have the hole drilled in the thermostat, and there's a small 'thingy' in there that sorta closes the hole. It's to 'auto burp' your cooling system. Or attempt to.

Fluid/air will not exit through your overflow because the radiator cap prevents fluid escaping through that hose to the overflow unless there's enough pressure to open the cap. Take your cap off and look, you'll see.

Burping is a real issue, it's especially important on older Renix Jeep Cherokees, and other vehicles with surge tanks. Most of the time it kinda works itself out when you fill your radiator, and let it run for a bit to circulate, also helps if you park on a slight incline so your radiator, radiator cap is the highest point in the system.

If you had a head gasket leak, you'd see coolant leaking, or see/smell coolant in your exhaust and you'd notice a loss of coolant in your radiator.

Those who've worked on water pumps (not engine, actual big water pump) know how air gets trapped :D Its a PITA.
 
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