Exhaust pipe heating up oil pan

I would like to know what yall think about this. I have a 99 4.0 with 96k. It has a slight tick that has developed in rear engine area. After laying under my jeep looking up at my now leaking rear main, it hit me. I got my temp gun out and holy crap!! My block at the rear just above the pan was 382F ! the front was like 178F. I also notice a bend in the pipe just south of the manifold. I have a 91 cherokee that also has this bend or pinch in the pipe. Why is that bend there? Last but not least could the 600F exhaust pipe be overheating the back of the engine/tranny? Why is this pipe ran so close to the oil pan theres a tone of space to move it. Have any of you noticed this and fixed it? It seems it would make the engine life longer to move this pipe.

Your heat gun was picking up the heat form the ex pipe not the block.

flash.

I believe that "bend" in the downpipe is there for driveshaft clearance.

anyone else believe that the engine itself was not reporting that heat level?

BoC said:

I would like to know what yall think about this. I have a 99 4.0 with 96k. It has a slight tick that has developed in rear engine area. After laying under my jeep looking up at my now leaking rear main, it hit me. I got my temp gun out and holy crap!! My block at the rear just above the pan was 382F ! the front was like 178F. I also notice a bend in the pipe just south of the manifold. I have a 91 cherokee that also has this bend or pinch in the pipe. Why is that bend there? Last but not least could the 600F exhaust pipe be overheating the back of the engine/tranny? Why is this pipe ran so close to the oil pan theres a tone of space to move it. Have any of you noticed this and fixed it? It seems it would make the engine life longer to move this pipe.

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What are the specs on the "Heat Gun"?

Is it infrared.

Does it have a laser sight?

Is there a leak in the exhaust pipe near the engine that part of the engine?

riverfever said:

I believe that "bend" in the downpipe is there for driveshaft clearance.

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This is what I have always understood. The 00+ have the LP30, and hence no pinch.

Ecomike said:

What are the specs on the "Heat Gun"?

Is it infrared.

Does it have a laser sight?

Is there a leak in the exhaust pipe near the engine that part of the engine?

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Thats a good point! If the ext leak was pointing toward the part of the oil pan then.................. the pan could be that hot!


Flash

The pan could get that hot and maybe the bellhousing but the block should stay pretty cool. thats alot of thick metal

1985xjlaredo said:

The pan could get that hot and maybe the bellhousing but the block should stay pretty cool. thats alot of thick metal

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If your pan was that hot your oil would literally catch fire in the pan. Not likely.

It is a laser sight temp gun very accurate used to measure bearing temps. I sighted in at the block just above where the pan bolts to the rear of the block. Sorry it took me awhile to get back to this, but Ive been driving and my oil pressure is staying alil higher @ idle, since i used a bottle jack and a brick to move the pipe away from my pan. lol now i have a clamp rubbin in the back :O It just seems logical that if you have a 600 degree pipe 2inchs from the oil you would like to keep cool,it is not good. That heat over a long haul im sure manages to creep thru all that thick block metal and on to rear engine parts, whick would prolly expand them and make them leak like the rear main oil seal area. Just a thought. Thanks for the responses.

Did you measure the temp of the exhaust pipe itself?

Evan99 said:

It is a laser sight temp gun very accurate used to measure bearing temps. I sighted in at the block just above where the pan bolts to the rear of the block. Sorry it took me awhile to get back to this, but Ive been driving and my oil pressure is staying alil higher @ idle, since i used a bottle jack and a brick to move the pipe away from my pan. lol now i have a clamp rubbin in the back :O It just seems logical that if you have a 600 degree pipe 2inchs from the oil you would like to keep cool,it is not good. That heat over a long haul im sure manages to creep thru all that thick block metal and on to rear engine parts, whick would prolly expand them and make them leak like the rear main oil seal area. Just a thought. Thanks for the responses.

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Was it 2 inches behind the block or 2 inches under the block, or some combo of those?

Your theory is sound, but I would still look for a small, even a tiny pinhole leak in the pipe itself. Take it to a muffler shop and they will usually check it for free. A 2 inch proximity with the car moving and no pipe leaks does not sound that bad, but even a tiny exhuast pipe hole in the pipe blowing on the block/pan area would sure do it!

I had an exhaust pipe 3/8" from the drain pan bolt on my diesel for three years with out any problems (that I noticed) other than it was a pain to drain the oil!!!

Dave4.0 said:

If your pan was that hot your oil would literally catch fire in the pan. Not likely.

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First off the oil would not be that hot, just the outside surface of the block/pan.

Heat transport is a funny thing. It is possible for the outside surface to get that hot if the exhaust is blowing right on it constantly, but the internal metal surface temperture would be a lot cooler. It has to do with heat transport rates.

The rate of heat added to the metal exterior, the rate of heat transport through the bulk metal. Then the rate of heat transport from the inside metal surface to the oil and and coolant. My bet is it is heating the outside surface a bit faster than the metal can conduct the heat away from that surface, resulting in a large temperature increase at the surface near his exhaust pipe.

Just for fun sometime check the exhaust manifold temperture (if you have a way to test it) at various spots and the engine block where the exhaust manifold is attached to it and see the large temperature gradient from one to the other.

Or try heating the surface of an engine block with a blow tourch on one side and hold your hand on the other side at the same time!

hey just a question, i have a 90 that has the pinch in the downpipe, someone stated above that the LP30 models do not have the pinch. can i swap the LP30 downpipe into my 90 to rid of the pinch for better breathing? since its lifted the driveshaft shouldnt come close to the pipe. although im sure it wont fit since those models have a whole different setup.