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Old 10-19-2009, 10:02 PM
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Strange overheating/Idle issue.

Let me start with a brief run run down on what is going on here.

I bought this truck, 1988 Chevy 2500 350 4x4 about 6 months ago. The truck was sitting for about a year before I bought it, and i was able to jump start the truck and drive away in it. After giving it a brief overlook, i replaced the battery, and drove it around town for a few weeks, putting 200 ish miles on it, without replacing anything but the battery. I moved about 160 miles away, and loaded up my truck and drove out of town. I made it to my new place just fine. I drove the truck for a few more weeks, with no issues. One day i went outside to start it up, and the truck would turn over, but would not maintain an idle, without me messing with the gas peddle, to massage the thing to stay running. If i gave it no gas, it would die, if i gave it a little gas, it would try to rev up, but still want to die. I was stuck in this loop of giving it a little gas, and letting back, then giving it gas, etc... The only way to keep the truck running.

From this i determined that I had a fuel distribution problem, so i started picking apart the fuel system. I started with a new inline fuel filter, when that didn't do it, i went ahead and gave it a standard tune up. New cap, rotor, plugs, plug wires, making sure i maintained the correct wire pattern.
Still had to do the same gas, no gas rhythm to keep it running...

I went ahead and replaced the TBI gasket, and that helped.. kinda... the gas, no gas rhythm was delayed out a little longer, by just a second or so more per gas, no gas rhythm cycle.

I dropped the gas tank and replaced the fuel pump, making sure i changed everything out correctly, etc. This solved the gas, no gas issue.

The truck now idles without any human intervention. After letting it run for 10 minutes, i noticed that the temp was around 220, so i turned off the truck.

I went ahead and replaced the water pump with a factory replacement (brand new one, NOT a referb) and replaced the bottom supply hose that goes from the bottom of the radiator, to the water pump. I also replaced the thermostat.

The truck still over heats. I can run the truck with the radiator cap off, and see the water moving, but it seems like the thermostat never opens (195 deg.)? I pulled the new thermostat out of the truck, and put it in a pan of boiling water with a thermometer, and it does open at around 195 deg, so that's not the issue. I also noticed that i correctly installed the thermostat with the spring part pointed into the engine. The cooling system has no leaks, that I am aware of, and have thoroughly checked out all the places where it could leak.

My question is:

What should I pick apart next? I did find a post in this forum about parking the truck at an incline, so that any air would make itself come towards the cap? I'm guessing i have an air bubble in the block, since i did replace the water pump, and the fluid level in the cooling system did drop considerably from that.

Also, The truck still inst running correctly. When i go to rev up the RPM's of the truck, it wants to stutter, almost stalling out, but doesn't die. I can back off the gas and the truck returns to an idle, and runs fine until it over heats.

I am wondering if these two issues could be related.

Another possibility is that there is a bad "mass air flow" sensor that could be creating an in correct fuel/air ratio, making the truck run really lean, therefor causing the over heating issue???

I'm stumped on this one guys. Any advice on what i should focus on next would be greatly appreciated!!

Thanks!

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Old 10-20-2009, 04:55 AM
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Have the engine tested for hydrocarbons in cooling system (leaking head gaskets). Simple test that will save a lot of time.

Fuel problem sounds like a bad tank of gas.
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Old 10-20-2009, 09:46 AM
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I was talking with a few mechanic friends, and one of them said that i should have had the gas tank cleaned out when i dropped it to replaced the fuel pump. I did put a bottle of fuel system cleaner into the gas tank, and im hoping that might take care of some of it....

My thinking is that I should focus on the cooling system system first, so that i can run the truck for more than 10 min at a time. And then address the fuel system issues. I was curious to hear what you guys had to say about these two issues being related or not.

Is there a "do it yourself" way to test for hydrocarbons? I can run out and check to see if there is any white foam in the oil... Would that be close enough, as a do it yourself option?

Thanks again.
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Old 10-20-2009, 03:16 PM
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I just checked the oil, and it looks clean. No hint of white or foam in it at all.

Is there a more definitive method that I can do myself to test this? Do you think i should pull the heads, and look at the seals? I would have to find a guide online to do this though. I don't mind doing whatever I need to do, i am playing catch up on the learning curve thought

Thanks again guys!
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Old 10-20-2009, 04:44 PM
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Any professional auto service will have a setup to check for hydrocarbons in the coolant. Call around and get prices for a test. Save you a lot of money and labor in the long run..
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Old 10-21-2009, 04:17 AM
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are you sure you have the correct water pump?88 is one of those years that can be either reverse or standard rotation depending on belt setup.Full serpentine setup was reverse rotation, standard vee and flat belt was standard rotation, you could have been handed the wrong rotation pump when you did the replacement.
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Old 10-21-2009, 02:49 PM
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I just called the parts store where i bought the water pump, and we verified that the part number of the pump I have is the correct one to run with the serpentine belt my truck uses.

I also verified that the radiator is not clogged, or has any major blockage, and I can see daylight through all the fins in the radiator.

I also did run the truck last night without the thermostat installed, and the truck seemed to not over heat at idle like It had before with the new factory replacement thermostat installed. I did verify that the thermostat does function correctly. I put it in a pot of water, and brought it to a boil, and noticed that the thermometer was reading around 195 deg, when the thermostat opened. I removed the thermostat from the water, and watched it close again.

With this said, I am leaning towards the idea of an air bubble in the system somewhere...

Should I place the thermostat back into the system, and run the truck some more? park the truck at an incline, so let any air escape?

Or is there something else I'm missing here...

Thanks.
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Old 10-21-2009, 04:23 PM
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A leaking head gasket will put air into the system. Thats why the hydrocarbon test. Air bubbles= no cool!!
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Old 10-22-2009, 06:31 PM
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Well, this morning i was able to run the truck for over 30 min without the thermostat in the cooling system without the temp getting past 160ish.

I replaced the thermostat, making sure it was properly installed, via online references, and the Chilton book i bought, and now the truck over heats within about 10 minutes at idle.

I am pretty sure the clutch fan is shot. Was thinking about replacing it with ether another clutch fan, or a flex fan, suggestions?

I am also leaning towards the idea that there is air bubbles/pockets in the system. I filled up the "boil over/reserve tank" with about 3/4 water, and after i let the truck run and over heat, i crack open the safety lever thing on the radiator cap, and from what I can tell, air bubbles are coming out. I'm guessing that as the engine cools, it will suck in fluid, and not more air from the tank being empty from before?

I don't feel that the truck is running well enough to drive it down to have the fluid tested for hydrocarbons. I would assume that i could just drain off a portion and bring that in? Probably best for me to just call the mechanic and see for myself on this one.

Thanks.
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