1981 k5 blazer th350 boiling fluid?

DnS421

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Hey guys, I have a 1981 K5 blazer 4x4 with 350 and th350 trans and it’s been sitting for 20 years, I changed the fluid and filter and started the truck to see if it would move, it engages all gears fine and I went about ten feet in drive and about ten feet back in reverse and when I shut off the truck I could already hear boiling in the pan. What should I check? I’m thinking something is clogged?
 

Bextreme04

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Hey guys, I have a 1981 K5 blazer 4x4 with 350 and th350 trans and it’s been sitting for 20 years, I changed the fluid and filter and started the truck to see if it would move, it engages all gears fine and I went about ten feet in drive and about ten feet back in reverse and when I shut off the truck I could already hear boiling in the pan. What should I check? I’m thinking something is clogged?
What do you mean by "boiling in the pan"? Did you check fluid level while running? Does it have a cooler? Radiator only or external cooler also? Have you checked the line temps? Is it boiling out the vent line?
 

Itali83

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I’m betting your transmission vent tube is plugged. Probably with a mud dauber. My truck sat for 20 years and that was the issue. Mine would actually push fluid out the top of dipstick tube when I started it.

Ben
 

DnS421

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@Bextreme04 it has an external cooler, never had any fluid out of vent tube, have not checked the level while running or the temp of the lines. It’s making a boiling/bubbling/popping noise inside of the pan.
 

DnS421

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@Itali83 how did you fix yours? I’ve heard of using a drill but small enough to fin in the hole and hand twisting it to dig out dirt
 

Bextreme04

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I would start with the simple stuff... make sure it is properly filled by checking it on level ground while running in park. You will have a cold fill level spot. Once you know it is properly filled, see if you have the same sound. Can you take a video of it making the noise and post it?
 

Itali83

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@Itali83 how did you fix yours? I’ve heard of using a drill but small enough to fin in the hole and hand twisting it to dig out dirt
That should work. Honestly. I’ve been too busy to actually fix it. It’s just a little low on fluid and doesn’t do it anymore. Savage but I just didn’t have the time this winter to fix that.

Ben
 

DnS421

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@Bextreme04 i will do my best to get a video of the noise for you, I’m gonna try cleaning the vent tube then trying again
 

Matt69olds

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I doubt the fluid is boiling, especially only driving it a few feet. More than likely your hearing the converter draining back into the pan, or just normal fluid settling.

I would agree with checking the vent. If it’s plugged, it can force fluid up the dipstick tube. Maybe that’s what your hearing?
 

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