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Discussion Starter · #1 · (Edited)
I want to change the thermostat in my '79 305. I'm worried, though, about the two neck bolts. The hose has leaked over time, and has corroded the whole neck area- I just wire brushed it when I replaced the hose and t bolt clamp. Gave the bolts a little tug with a 3/8" ratchet, but they're solid. Should I spray penetrant and gradually upgrade my leverage (1/2 ratchet> breaker bar> 3/8" IR impact gun)?
What's the likelihood of one or both bolts snapping off in the manifold? Has anyone dealt with the same situation?
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87 Caballero Amarillo, stock 305/200R4/QJ
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When you get the bolts out, chase the holes first. Use the right size tap and run it down in stages, ½ turn forward, ¼ turn back. Use PB or another of your choosing to keep the tap soaked. Then blow the holes out well (use eye protection). That'll get rid of the majority of rust, crud, grime, buildup, whatever is left over from the bolts. Then decide if you need new bolts or not. Use grade 5 if you do.
 

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Discussion Starter · #6 ·
I'm reassured that nobody has yet replied having had the bolts break off in the manifold. Tom's comment about them being seized in the housing, not the intake, makes sense.
 

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Use a good penetrating oil, let soak, smack the bolt heads with a ball peen hammer and if they don't break loose try tightening a little.

Work them back and forth while spraying with oil.
 

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Discussion Starter · #8 ·
When you get the bolts out, chase the holes first. Use the right size tap... then decide if you need new bolts or not. Use grade 5 if you do.
Advice appreciated- going to do exactly that, and plan ahead (first spray bolts) before I proceed. Might just go ahead and replace the corroded neck assembly and sensor. Would there be any problem using stainless bolts here?
 

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One of the best ways to get bolts and nuts to release is to apply heat sparingly. Lately, at SEMA, many of the vendors were demonstrating new tools which created heat by electromagnetic induction. The physics principles are similar to those found in glass top stoves. Unfortunately, these tools are expensive! So, for me I apply heat using a propane or map gas torch. Sometimes, you can get lucky with a heat gun. In your case, I would focus the heat on the intake manifold outside of and around the base of the sensor. All you really want to do is cause metal expansion to break any kind of bonding that have developed between the pieces. It is also definitely a good idea to remove or shield the areas you don't want the flame to burn and/or damage nearby components. Good luck!
 

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Stainless steel is just an alloy of steel mixed with chrome. There's different hardness factors depending on the exact mix ratio, but generally there's little benefit to using stainless bolts as they are usually too brittle. Like grade8 bolts, they have a higher carbon composition, so take torque very well, but don't take impacts well at all. That's why most bolts you'll find on a Chevy are grade5, they have a little more 'give' in high stress situations, like seat bolts etc, and will bend or warp rather than sheer.
 

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Advice appreciated- going to do exactly that, and plan ahead (first spray bolts) before I proceed. Might just go ahead and replace the corroded neck assembly and sensor. Would there be any problem using stainless bolts here?
300 grade stainless is perfect for what you are trying to do. If you have a cordless impact driver you can use that in short bursts to help get the bolts free. Heat and Kroil or PB blaster will also help.
 

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What 11thhourfabricat said about a cordless impact gun, NOT AN AIR IMPACT. I replace tankless coils in boilers at work and many have difficult bolts. A cordless impact helps jar the bolts without breaking them.
 

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What 11thhourfabricat said about a cordless impact gun, NOT AN AIR IMPACT. I replace tankless coils in boilers at work and many have difficult bolts. A cordless impact helps jar the bolts without breaking them.
ok, I'll bite, what is the difference between "cordless impact" and "air impact"? (other than battery vs air-power) don't they both have similar torque ratings?
 

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Torque hammer. A regular cordless can get the torque, but has much 'softer' hammers than an air impact which has 2x or 3x the breakaway. That's what snaps bolts unless you check the settings
 

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Discussion Starter · #16 ·
Excellent insights on the air impact, which was going to be my last method. Come to think of it, on the good car repair youtubes they seem to zip everything out with a battery impacts (Milwaukee?).

Where have other gen 5 owners ('79) had luck sourcing the old style two port sensors? Rockauto and other online show blade type connectors. Oem Chevy dealer ?
 

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You mean a 2 port thermal vacuum switch?
ACDelco Professional 212-631 EGR Thermal Ported Vacuum Switch Amazon.com: ACDelco Professional 212-631 EGR Thermal Ported Vacuum Switch : Automotive
Like this one?
Or this one?
You keep saying 'sensor', but the sensors have a blade attachment as they report to the ECM via wiring. The 'switches' use vacuum to on/off and either allow or deny vacuum according to coolant temp.
 

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In response to the OP's question on breaking bolts, that did happen to me on my '85 Monte Carlo SS. One of the bolts broke off in the manifold. I believe the difference is the Monte SS engine has an aluminum intake where the El Caminos all came with cast iron manifolds. Looked to me like corrosion between the steel bolts and aluminum manifold.

Had to remove the intake and take it to a machine shop to remove the broken bolt and chase the threads. At the time I didn't apply any thread soaker because I assumed they would come out (they always had before!).

From your photo, yours don't look bad but it would be prudent to apply PBblaster before trying to remove them.

On my Monte, ever since, I remove the bolts one at a time every few years, clean the threads and apply anti seize to the threads. As a precaution I also do that on my 87 Camino and haven't had any problems since.
 

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Discussion Starter · #19 · (Edited)
Lately, at SEMA, many of the vendors were demonstrating new tools which created heat by electromagnetic induction. Unfortunately, these tools are expensive!
An excellent suggestion, I've heard of them and am going to research. Best thing would be if an auto supply place would rent them- new they run $180- $530 (NAPA). I'm not going to use an open flame next to the carb and so many rubber vacuum and fuel lines. https://www.amazon.com/dp/B095WZJQ9...1085470220.1638083162&tag=shopperz_origin1-20

I have sprayed the bolts with Sea Foam Deep Creep, which came out on top of Project Farm's comparison.
 
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