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Scared to loosen 18 year old thermostat bolts!

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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98V70T5
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Scared to loosen 18 year old thermostat bolts!

Post by 98V70T5 » Fri Dec 09, 2016 7:14 am

This may sound trivial, but I am trying to change my thermostat. I believe I have the correct Torx bit (T-35), and it does fit correctly. The thermostat is original to the car, 18 years old, and I feel the bolts are slightly corroded on the threads internally in the housing, and held tightly. To practice I went to the junkyard, and found the same year car. I was able to just barely crack the front bolt, but the ratchet was just on the limit of wanting to "walk out" of the top of the bolt, but it did crack it. I tried the rear bolt, and I couldn't put enough downward force on the tool to keep the bit in the bolt head, and the worst thing happened, the tool walked out of the bolt and stripped the head! Had this been my car, I would be in a real dilemma right now.

So, I am asking the community, what is the best way to ensure this won't happen. Is there a more correct Torx bit to use? By that I mean, I have another car that uses a T-50S bit, which is a little different that a standard T-50. If you use a T-50, it will appear to fit, but will round out the bolt, upon removal. I have thought about getting an impact driver, some of you might know what that is, but basically it's a tool that allows you to hit the top of the driver with a hammer, while at the same time, it applies a twisting force. It's used a lot on Phillips head bolts, in the motorcycle world. Is this something I need to use? What tips do you have? I do not want to round out the bolt head! Thanks!!

macs70GLT
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Re: Scared to loosen 18 year old thermostat bolts!

Post by macs70GLT » Fri Dec 09, 2016 8:06 am

My favorite penetrating oil is PB Blaster. You can spray that on the bolts & let it seep in for 10 minutes or so. You can also do it a couple of times over a day to be sure.

Good job with trying it out at the junkyard.

I think some have replace these bolts with a hex head fastener, I'm not familiar with the other type Torx you mentioned.
Lars: 1988 245, 250K mi retired
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Re: Scared to loosen 18 year old thermostat bolts!

Post by kahl » Fri Dec 09, 2016 8:50 am

I would be hesitant about using the hammer impact drive on a thin aluminum casting. If your you could moderate the hammer blows you my be OK. I have used the method Mac has described with success.

scot850
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Re: Scared to loosen 18 year old thermostat bolts!

Post by scot850 » Fri Dec 09, 2016 9:32 am

+1 to the recommendations mentioned. I bought a set of long reach 3/8" torx sockets. I let the bolts soak in PB Blaster or I also use Deep Creep and let them soak with re-applications for a day or 2. Then before trying to remove, I put the Torx socket in the bolt head and give it 2 or 3 taps on the end with a hammer to try to shock the threads loose. Problem is the use of steel bots in an aluminum casing. I had to replace the thermostat in a 97 850 recently and this worked for me, but I am realistic enough to realise I may have to buy a replacement thermostat housing if it goes wrong. I'm just surprised I haven't already got one in my stash!!

Neil.
2000 V70 R - still being an endless PITA
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Re: Scared to loosen 18 year old thermostat bolts!

Post by rguzz » Fri Dec 09, 2016 9:44 am

Try this. I used bolts from an intake manifold from salvage yard which are perfect fit.

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erikv11
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Re: Scared to loosen 18 year old thermostat bolts!

Post by erikv11 » Fri Dec 09, 2016 9:44 am

The correct size is standard T40, it sounds like maybe that is the main problem? Also I won't touch those without a long shafted torx bit, so that you are able to go straight down on that rear torx head. It is crucial to use a quality bit that you can point straight down.

The screw the dealer sells now for that application is an updated screw that is still torx but made of a different metal that won't strip out so easily, or just use hex as mentioned. Cam cover bolts are the perfect size if you have access to a parts car or junk yard.
'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 285k
'06 S60 R, 165k
'99 Camry V6 :shock: 125k
gone: '96 NA 850 210k, '98 NA V70 182k

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skloon
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Re: Scared to loosen 18 year old thermostat bolts!

Post by skloon » Fri Dec 09, 2016 9:50 am

Long shaft socket and do it when the engine is warm it should expand the aluminum more than the steel bolt - spray pb blaster when it is hot too

cn90
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Re: Scared to loosen 18 year old thermostat bolts!

Post by cn90 » Fri Dec 09, 2016 9:59 am

These are my tricks:

1- Spray PB Blaster every day for a good week before the job.
You need to get PB Blaster.

2- Use Torx 40 as erik mentioned. The rear bolt requires a universal joint for best angle.
Whatever you do, the T40 tip needs to sit deeply inside the bolt.
BTW, clean any debris inside the bolt head first!

3- I tighten the bolt a tiny bit first just to break the bond, then undo it.


Tstat.jpg
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2005 XC90 2.5T 110K+

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erikv11
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Re: Scared to loosen 18 year old thermostat bolts!

Post by erikv11 » Fri Dec 09, 2016 10:08 am

It obviously works fine for cn90 but I wouldn't use a U-joint if you are concerned, because you lose the ability to apply good strong downward pressure. Using a long-shafted torx you can go straight down.

+1 to all the recommendations to use a good penetrant. PB Blaster is great, Liquid Wrench has tested out even better than PB, and better than either is home-brewed 50:50 acetone:ATF.

These pretty much always come out fine if you are careful, good on you for thinking in advance about how to do it right.
'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 285k
'06 S60 R, 165k
'99 Camry V6 :shock: 125k
gone: '96 NA 850 210k, '98 NA V70 182k

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firestarterpro
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Re: Scared to loosen 18 year old thermostat bolts!

Post by firestarterpro » Fri Dec 09, 2016 10:11 am

I was scared too, and brought it to a mechanic shop and he broke the bolts loose for free. It was an really old guy, and i mean that to say he wasn't very strong in appearance. He didnt charge me a buck, just told me to buy a breaker bar.
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