Engine/Transmission (1998.5 - 2002) Heads up - thermostat housing bolts...

[wlowe]

I changed my water pump, thermostat and belt today. I tightened the thermostat housing bolts in a circular pattern with my torque wrench set at 18 ft lbs. until one bolt clicked. The other two bolts kept turning and I started getting nervous that I might be over torqueing. Then one of the bolts snapped and I thought I was in trouble. Luckily the bolt came out easily without the use of an easy out.



At first I thought my torque wrench was out of adjustment, but after looking at the bolts I found that the two bolts that kept turning where about an eighth of an inch longer than the one that torqued to 18 ft lbs. I looked in my parts manual and there was only one part number for these bolts so I knew that they should all be the same length. I'm not sure, but I think the two longer bolts may have been bottoming out before completely tightening down.



Also, after doing a search here on the TDR I found that the service manual lists the wrong torque for these bolts. The service manul lists 18 ft lbs,( 24 nm), but according to some of our members the recommended torque for an 8mm bolt is 9 ft lbs,(12 nm). I also found a couple of instances of members breaking these bolts when torqueing to 18 ft lbs.



I ended up getting some metric grade 10. 9 bolts at the hardware store with 10 MM heads and torqued them to 10 ft lbs. Just a heads up for anyone changing their thermostat.

 

[Joseph Donnelly]

The proper torque for M6 x 1. 0 high grade bolts is about 89 inch pounds (like injector hold down bolts), or about 7 ½ ft-lb. M8 x 1. 25 thread bolts on our Cummins engines should be tightened to 18 ft-lb. You had two bad bolts. Most Cummins M8 bolts are grade 9. 8 or 10. 9; the latter compares to American grade 8.

 

[wlowe]

The proper torque for M6 x 1. 0 high grade bolts is about 89 inch pounds (like injector hold down bolts), or about 7 ½ ft-lb. M8 x 1. 25 thread bolts on our Cummins engines should be tightened to 18 ft-lb. You had two bad bolts. Most Cummins M8 bolts are grade 9. 8 or 10. 9; the latter compares to American grade 8.

The bolt I purchased to replace the broken bolt was an M6 X 1. 0. At first I assumed that they were 8 MM bolts because that is what was quoted from older TDR posts. After reading the post again I think they were referring to a bolt with an 8MM head and a 6MM body. Below is one of the posts I was referring to:



https://www.turbodieselregister.com...1998-5-2002/54983-thermostat-bolt-torque.html

 

[Joseph Donnelly]

12 valve engines use M8 for the thermostat housing. 24 valve, including HPCR, use M6 bolts there.

 

[wlowe]

12 valve engines use M8 for the thermostat housing. 24 valve, including HPCR, use M6 bolts there.

Thanks for the info Joe, that explains some of the confusion. It also explains why the bolt snapped using 18 ft. lbs. of torque. Maybe the 2001 service manual, which states 18 ft. lbs. , was never updated from the 12 valve engine service manual.

 

[TBartlett1]

Thermostat housing bolts

On a several occasions I have gotten into trouble torquing bolts on non critical items such as your thermostat housing in an effort to do a good job by the book.

When using a torque wrench you tend to put your faith into the torque wrench and ignore the feel of the bolt being tightened because you are listening for the click or watching the needle. Torque wrenches being larger than most wrenches or ratchets tend to minimize the feel required to realize the fastener is yielding.

Buy the time you realize something is wrong threads are stripped or compromised or bolts are stretched or broken.

In the past I have also found factory manuals publish wrong torque values.

Also be aware that most torque values are for clean dry threads or lightly oiled with engine oil.

The use of STP or other lubricants that drastically reduce friction will cause the fastener to be over torqued (over tensioned)

My advice if you insist on torquing smallish fasteners is to start at 50% of torque value and work towards 100% while being aware of how the fastener feels. If the dial stops increasing in value stop!!

In situations like your thermostat housing tightening the bolts until they are all snug then going ¼ to ½ turn should be good.

My 2 cents

Tim

 

[wlowe]

On a several occasions I have gotten into trouble torquing bolts on non critical items such as your thermostat housing in an effort to do a good job by the book.

When using a torque wrench you tend to put your faith into the torque wrench and ignore the feel of the bolt being tightened because you are listening for the click or watching the needle. Torque wrenches being larger than most wrenches or ratchets tend to minimize the feel required to realize the fastener is yielding.

Buy the time you realize something is wrong threads are stripped or compromised or bolts are stretched or broken.

In the past I have also found factory manuals publish wrong torque values.

Also be aware that most torque values are for clean dry threads or lightly oiled with engine oil.

The use of STP or other lubricants that drastically reduce friction will cause the fastener to be over torqued (over tensioned)

My advice if you insist on torquing smallish fasteners is to start at 50% of torque value and work towards 100% while being aware of how the fastener feels. If the dial stops increasing in value stop!!

In situations like your thermostat housing tightening the bolts until they are all snug then going ¼ to ½ turn should be good.

My 2 cents

Tim

Yea, from now on I'm going to use the feel method for tightening small low torque bolts. I purchased this torque wrench for adjusting my transmission bands and it works well for that. It goes up to 240 inch lbs. , (or 20 ft. lbs. ), so 18 ft. lbs. was at the upper end of its range which may cause it to lose some accuracy.