Air pockets in cooling system...

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I've been trying to burp my cooling system on a 408w without any luck and this is by far the biggest pain in the ass I've ever had trying to do it. Its got a nasty air pocket that is causing the thermostat to pop open and closed for several seconds when it gets up to opening temp. While its doing this, the temp gauges are all over the charts. I'm actually running two temp sensors -- one going to an autometer gauge and the other going to my EFI (I can monitor it on a laptop). Often times, one is reading the correct temp (or at least what I believe to be the correct temp), while the other is pinned.

Does anyone have one of those Snap On (or similar) vacuum fill tools that fills the system under pressure? I would be more than happy to drop down a deposit until I returned it, or if anyone has any suggestions, I would appreciate it. I'm in San Diego.

Thanks,
Andy
 

steveG

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Rather than try to work around the problem, I think you'd be better off fixing the cooling system so it doesn't develop air pockets. The cooling system on your truck is pretty much standard, isn't it?
 

manicmechanic

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Some of them are a pain. I have used the "fart in the bottle method".
It amounts to placing a jug of coolant up high like on the roof and removing the check in the radiator cap then run a hose from the radiator overflow fitting to the jug. when it blows bubbles in the jug shut down and wait until it draws coolant, repeat until system stabilzes. Swap caps and your bled.
I agree that the fill point should be highest by design but some engines have air pockets and remote coolers.
 

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I used to have restrictor plate instead of a thermostat and didn't have any problems, except it would barely get up to temp. So I decided to get a thermostat. Since then, I've had no luck
 

steveG

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You could try drilling a small hole in the thermostat (some are this way new). Is the upper radiator hose the highest point in the cooling system? If it is, you could try adding a fill point in the hose. V8 Dakotas have the fill point (radiator cap) in the upper hose. I used one on the upper rad hose on my V8 Ranger that had a bed mounted radiator.

Do you have any under-hood pics of the truck?
 

manicmechanic

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You could try drilling a small hole in the thermostat (some are this way new). Is the upper radiator hose the highest point in the cooling system? If it is, you could try adding a fill point in the hose. V8 Dakotas have the fill point (radiator cap) in the upper hose. I used one on the upper rad hose on my V8 Ranger that had a bed mounted radiator.

Do you have any under-hood pics of the truck?
Good point on the bleeder, the T/stat wont open if it is not submerged. I have noticed some T/stats have a bleeder hole and some dont, probably helps.
 

gcddarren

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put a petcock bleeder valve. radiator drain valve or the same type of bleeder on the bottom of an air compressor. put it on a high point. just start up your car get it warm, shut it off and blead out the air/steam. keep doin it till your a steady stream of water come out. works great.

we dont run a thermostat, we have restiction washors. be shure you dont have a blown headgasket bc that will mess with the temp! that was our problem for the longest time. we moved the radiator to the back and thought the pump couldnt pump enough to the radiator so we put on a high volume pump. same problem. it was a small leak on the headgasket. temp would start out good for 10 min then it would skyrocket up to 250 plus.
 

NicksTrix

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your radiator filler cap should be the highest point in your system. does your upper hose run higher than the cap? if so you'll need to fab a splice with a bleeder to ensure you are purging the system.
 

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Based on your replys, here is some additional info:

- The filler neck is either level with or slightly above the upper radiator hose.
- I drilled a 3/8 hole in the thermostat before installing it.
- I dont think the head gasket is blown because it only gets hot until the thermostat opens up (read my original post about what the t-stat does when its opening), then immediately cools down once open.
- I have two coolant sensors; one just behind the thermostat that goes to my dash gauge, and one on the driver side of the intake manifold which the EFI reads from. When the dash gauge was reading 160-170, the EFI was pinned at 235. As the thermostat began opening, it would pop open and closed several times and the dash gauge would climb up to 200+ until it finally opened, then would drop back down to 150-160. Even after the dash gauge dropped back down to 150ish, sometimes the EFI temp readout would still stay pinned at 235, sometimes it would drop back down and read the same temp as the dash.
 

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your radiator filler cap should be the highest point in your system. does your upper hose run higher than the cap? if so you'll need to fab a splice with a bleeder to ensure you are purging the system.
If there were the case, would I still be able to bleed out all of the air with one of those vacuum air purging tools?
 

steveG

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The 3/8" hole is massive. Even a 1/8" hole would have been overkill... I should have given a specific measurement. Sorry.

Did it change anything?
 

steveG

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If there were the case, would I still be able to bleed out all of the air with one of those vacuum air purging tools?
Not necessarily. You can collapse hoses by putting a vacuum on the cooling system, but it ain't gonna collapse the intake and thermostat housing where your air pocket is.

Like I said earlier, you need to find a permanent fix. It's going to be a real bummer when you have to open the cooling system (or it's opened for you by a leak) in the desert at some point then have to figure out a way to pull a vacuum on it in the middle of nowhere.
 

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SteveG,

Sorry, it was 1/8 hole and I drilled it before I installed it the first time a few weeks back. So it was nothing new.

Also, if the filler neck wasn't the highest point in the system, wouldn't I have had the same problem when running the restrictor plate?
 

manicmechanic

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Seems like a mistake I made, One head gasket flipped over. Lots of coolant volumme masked the problem.
 

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Figured out the problem while trying to go to sleep last night. When I had the bottom end built, I told the builder than I was going to run a restrictor plate, so we plugged the two upper circulation ports on the water pump. After putting the thermostat in, I never reconnected the coolant bypass line that goes from the fitting on the water neck to the upper port of the water pump. Luckily I had drilled a weep hole in the thermostat so there was SOME water getting through, otherwise, it wouldn't have circulated any water through the motor before the thermostat opened up.

I put the fittings and bypass line back on this morning and viola, its fixed. I feel like such a bone head. Not I just hope I didn't damage the motor. All seems well, but it would pin the temp gauge for about 15-20 seconds while the thermostat was trying to open, then would drop back down to 160ish. Anything I should keep an eye on to determine if anything got too hot?

Thanks again for your suggestions.
 

scottm

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Huge temp swings are hard on the radiator and block. I used to work at an automotive research lab where we tested radiators to failure by cycling them with hot and cold water. A few moderate cycles won't hurt it, although it can crack if cold water gushes in when its super hot. I heard the head crack on my 74 mazda pickup back in highschool, when I put hose water in it when it had run completely dry. It sounded like it had been hit with a 5 pound sledge!
 

gcddarren

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Anyluck getting it fixed? and another idea is check and see when you hit the gas your soft hoses dont get sucked/pinched shut.
 
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