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Old 08-18-2011, 11:09 AM   #1
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Year: 92
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Thermostat

Okay,

So Ive emptied the bus and started a general tuneup, part of which was replacing a thermostat. Fairly simple procedure until one of three studs which hold down the aluminum thermo housing twisted off in it's hole. BLAST!

The vehicle is empty of coolant and I only managed to crack the footing on the aluminum cover with the easy out bits. I finally managed to drill the bolt out and have re-tapped it for a 3/8" thread. Of course when I ordered the studs at GM they are a metric #10-1.5.

Question: will I run into issues if I tap the correct thread into my 3/8" hole? Should I be very concerned about using a certain grade of stud to tighten down my thermostat housing, or will any steel bolt do the job? GM asks $9 per stud and Ive ordered them but for future reference do I want to make certain I have the studs labelled by the factory for each application, ei: a twin stud labelled "exhaust manifold" works?

Also: Ive ordered a new top thermo housing and in my neck of the woods it will take approx 2 weeks to arrive. I have plenty of jobs to keep me busy so I dont mind the wait but should I be concerned about leaving the cooling system empty of fluid for that time? Or should I temporary everything back together and refill the system?

Sorry, we're talkin about a 92 GMC 3500 Thomas Shorty here. 6.2 Diesel.

Thanks folks,

Serge
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Old 08-18-2011, 12:08 PM   #2
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Re: Thermostat

If you havr the holed tapped for 3/8", I would leave it alone. By trying to retap for 10 mm stud you may remove too much material and not get enough holding strength. As for the studs, yes you can use exhaust stud if you want. The studs are only a grade 5 for strength, you can use a regular bolt and tighten to approx 25-30 ft lbs. Hope this helps.
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Old 08-18-2011, 12:13 PM   #3
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Bolys and studs

Bolts and studs are designed for the job requirements. Bolts create what is known as clamping force. A thermostat housing does not require a great amount of force. The pressure is not high either at 15-16 pounds coolant pressure. Consider using a stud for the broken fastener. Frank
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Old 08-20-2011, 12:20 PM   #4
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Re: Thermostat

Thanks guys,

I will use the 3/8" exhaust studs to fill the freshly tapped hole and use the new factory studs to finish closing up the housing. I've never used any antiseize product but may do so in the hopes that this wont happen again. Thanks again. -Serge
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Old 08-21-2011, 12:49 AM   #5
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Re: Thermostat

Everything is all back together and now I wonder was there anything wrong with the thermostat to begin with? The reason I felt compelled to change it was a lack of heat come from the defrost heater. The issue seems to be the same as before....blowin cool air until RPMs come up. I know that I should get some heat before I engage gears and hit the road so......?

The underbody of my thermostat housing (crossover pipe) gets too hot to hold while my large top radiator hose gets medium warm.....it's pressurized but feels full of air.

Both hoses to my rear underseat heater get hot and stay that way until coming back into the engine compartment. I replaced both shutoffs to this heater which both get plenty hot.

The hose which leads into the below dash heater seems to not gain heat and is the same diameter as the hoses leading into, and returning from the back.

What else to say? Engine temp gauge reads normal operating temp and I need to maintain roughly 2000rpm for a minute or two to get some heat coming in.....the heat drops with the rpm back at idle.

Tomorrow I will try starting the engine with the rad cap off and topping the fluid while she idles.....seems I drained much more coolant than I refilled.

Any other suggestions?
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