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Weird Heating Problem HELP!!

C

cbarn65

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Oroville, CA
hey i got a 78 blazer, and even though i've replaced the radiator, water pump and thermostat, within the last 6 months... the damn thing suddenly started overheating, i mean i barely make it down the damne street and it hits white hot. I've run out of ideas and this is my first and only vehicle so if someone could help me out it would be awesome. thank you.
 
This could be any number of things:

1. Worn clutch on fan not allowing it to engage. Is the fan spinning? With the engine turned off, try to spin the fan, at operating temp it should provide pretty good resistance.
2. Thermostat failure. Even though you said you replaced it recently, I have seen them fail within a week. I would check this right after the fan clutch.
3. Failed water pump impeller. This is harder to check, since you need to see inside the pump, but you should be able to remove the lower radiator hose and see if the impeller is turning when you turn the engine by hand.
4. Headgasket failure. If it is this you will need to check the oil for any signs of water getting in. If the oil is a nasty color that doesn't look like black or very light brown then it may have gotten water in. Headgasket failure can also leak to the outside of the block, and you may have to examine the outside of the block for signs of water. Usually it will appear as white streaks going down the block from the bottom of the heads.

My money is on 1 or 2, but you will have to give a lot more information for us to determine exactly where to look. What engine is in it? Are all the belts intact? And more, I am sure.
 
If it happens in city traffic and is ok at highway speeds, it is the fan clutch. Happened to my 81 burb.
Tarey
 
it did fine for the last month and a half after sitting for about a year no overheating or nothing and then when i tried to correct the vacuum lines after it failed smog it suddenly started overheating out of nowhere, so i had the brand new thermostat in the truck with me cause i was gonna replace it after i put in the radiator last month anyway i just never got to it. so i put it in and i still kept overheating, white hot within a few blocks. the clutch fan works fine i checked it, and the guy at the smog shop checked and said the water pump was fine... so i dont know. its a 305 out of i dont know what and the guy before me rebuilt it pretty badass and put a cam in it, i dont know if that explains anything or not... and theres no white streaks or nothin going down the side and the oil looks good on the stick and was fine last week when i changed it...
 
if the carb is dumping to much fuel in it could cause overheating, but i would think there would be other symptoms as well
 
I ran into this last year- I have a 78 full size pickup. I had replaced the rad, water pump and thermo myself, but still had overheating issues.
At autozone or checker or whatever autoshop you have, grab a Prestone radiator flush kit. Very easy to setup and it will probably force you to change all your heating and cooling lines- but that's cheap.

You pretty much drain all the coolant, leave your drain plug out on your radiator then hook a water hose up to it and clear out all the lines by running water through this flush kit and turn on the truck, then running the heater. So your truck basically runs in idle while your hose is pumping water through all the cooling lines.

After a few minutes this think yellow gunk came spewing out- which i believe was caught up in the heater core. This fixed my problem, may not fix yours but for a $5 kit, $10 in new hoses and 30 minutes of time. Might be worth a shot.

prestonevn2.jpg


Good luck! and BTW- are you running your original mechanical fan or a new electric on your new rad?
 
Does this motor have an egr valve or remnants of one? Does it have any other driveability issues, like backfiring? I bought an '80's 350 motor site unseen. I installed it after checking bearings and the usual. Turns out, the way they had blocked off the egr was allowing full exhaust pressure all the time. Made it impossible to set dynamic timing and also made the motor get hot very fast!! The only reason I mention this is because you said you rearranged vac. lines. WAYY out in left field but imagine how long it took me to figure out.
 
If it goes white hot in just a couple of blocks and you are full of coolant, it almost has to not be moving water. I assume steam shoots out and the whole works right? Not just the temp gauge or light saying its hot.
Try turning the heater on high. Do you get lots of heat?
Let it get cool, take off the radiator cap, make sure its full to the top with coolant, and then crank it and let it idle while you watch the coolant. Don't Stand in the Line of Fire!!. If the coolant just sits there and then suddenly shoots out, the thermostat is messed up. The coolant should move up and down a few times as the engine warms up and then you should see some circulation. Feel the hoses. after it warms up they should both be warm all the way. If you do not have any heater heat, more than likely you do not have any water circulation. Either because of no water in part of the block or a water pump problem. A lot of newer cars can get an air bubble in the block and have special ways of filling the cooling system to prevent that. But I don't remember ever seeing a 350 do that.
However, I have once seen a water pump that the impeller was not on well. It would pump fine for a while, but after it warmed up, the impeller would expand slightly and start slipping on the shaft. At least that is the idea I am going with. The darn thing looked fine when I pulled it, and the impeller was tight. But, when things got warm, it quit pumping. A new one fixed it.
I have also seen a rebuilt water pump have the wrong impeller on it. But that one did not work right out of the box.
I have also see radiator hoses come apart inside and let a flap of rubber hang down and block flow intermittently.
Also, the radiator should be hot all the way up and down. if part of it is cold, you have a blockage. I don't know what would be blocked since its new, but you never know.
J.
 
yeah it has an egr valve and the vaccuum line diagram i have says that everything is hooked up right... im going to try the blockage kit, that just might do it. i tried the water pump and it seems to be doing fine, it circulates well and everyting and its a clutch fan, not electrical or whatever. I'll try each of these and let you know. Seriously, thanks a ton you guys...
 
Make sure that the lower radiator hose isn't sucking closed. This will cause your problem.
 
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