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Discussion Starter #1
Hey all, I am new on the forum and have a 1990 pickup. I recently rebuilt the head, put in an rv cam with new rockers. After getting it put back together I can only seem to get sporadic heat into the cab. It gets cold hot cold hot and so on. I have all the hoses hooked up correctly and the truck runs at the proper temp so I can't figure out whats up. Also the truck pulsates at idle until it gets good and warm (maybe related?)......any ideas? Really appreciate the help.
 

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have you bled your cooling system?
 

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Discussion Starter #3
No not yet although I may have figured out the problem. I had a couple loose bolts on the plate that attaches to the back of the head and I believe it was leaking a little coolant so the pressure couldn't be built up. I tightened them about a quarter turn but I have yet to start it this morning so I am not sure if it fixed the problem. So how do you bleed the cooling system? I've heard of a few different ways so I'm not all that sure. Thanks.
 

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Park the truck with the front up hill, remove the rad cap, set the heat to HOT, start it up.
As it warms up there will be some coolant overflow, don't worry. The air pockets work thru the system and out. May need a 2nd time if a lot of air got in.
 

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Discussion Starter #5
Ok went out to start it and at fast idle it (warming up) pulsates and the heat is intermittent but after getting good and warm the idle settles down and no pulsating. Every once in a while even warm I guess the idle will speed just a bit and start pulsating but it settles down quicker. Now the heat, after the truck is good and warm the heat settles down and blows warm fairly consistantly. I will bleed it later and see if that helps. Any more ideas? Thanks.
 

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Ok, I bled the coolant for a few seconds, it seemed like it started overflowing and burping bubbles out of it every few seconds, sound Like I did it correctly? Also it seems to surge when the brakes are applied. I took the vaccum hose off the break booster and it stopped the surging, what does this mean? Thanks.
 

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Rapidly changing hot and cold from the heater is indicative of very low coolant level.

I had the surging idle when I step on the brakes as well. The fix was to turn down the idle screw on the throttle body. Could also be the brake booster is leaking air, but get the idle screw set right first.
 

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Ok, I bled the coolant for a few seconds, it seemed like it started overflowing and burping bubbles out of it every few seconds, sound Like I did it correctly? Also it seems to surge when the brakes are applied. I took the vaccum hose off the break booster and it stopped the surging, what does this mean? Thanks.
A few seconds...I've seen wise old mechanics bleed cooling systems for 30 minutes or more. I suggest you let the vehicle run with the heater on "hot" for enough time for the thermostat to open up and then for the coolant to cycle through the system for quite some time for the system to rid itself of air pockets.
 

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Discussion Starter #9
Thanks for all the replies folks. I think I might have the surging under control.....hopefully.....How much antifreeze will come out of the system if I bleed it for a half hour? The problem I had before is the antifreeze was burbling onto the fan and the fan was throwing it everywhere. Will the overflow eventually stop (with coolant still in the system)? Also I think I have a small antifreeze leak on the driverside of the head right below the peice you hook on to lift it out. I suspect it is leaking out of that back plate on the head but does anyone know if there is any other place the antifreeze could leak out other than that back plate? Hopefully the head isnt cracked.....it was milled and hot tanked as part of the new top end. Any ideas?

By the way the booster only makes the engine pulse at high idle (like when just starting out in the morning). After warm it idles wonderfully.

Again thanks folks for the tips.
 

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How much antifreeze will come out of the system if I bleed it for a half hour?
Depends on how much air is in the system.

Will the overflow eventually stop (with coolant still in the system)?
Yes and you might even need to top off the coolant. If there is a large amount of air in the system, you may need to top off, let run a few minutes and if coolant is forced out, top off again and repeat until you have all the air out.
 

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Discussion Starter #11
Hey thanks for all the replies. I finally got the system bled and you all are correct there were a ton of bubbles in the system. After bleeding and adjusting the TPS it seems like the problems are totally taken care of (knock on wood - I've driven it just a few miles so hopefully the problem is done with).
 
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