Rebuilt 302 is overheating quickly
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More Turbo
Joined: Oct 2004
Posts: 621
Likes: 2
From: Marana, AZ
Ok, pulled the head off and I haven't found anything definative yet. Maybe you see something I don't. The rockers and push rods were all in tact, the head gasket looks fine to me, pulled the lifters out and they are fine as well. The port on #7 looks fine, I don't see any cracks anywhere. So what would cause a 10 psi compression check and the overheating that I am getting? Here are some pics of what I found:
Here is the block with the gasket still on:
Here is the block with the gasket off:
Here is the head:
Here is the gasket front side:
Back side:
Could it be possible the head is cracked in the port of the head where you can't see? But that would have no effect on the low compression reading I got.
Here is the block with the gasket still on:
Here is the block with the gasket off:
Here is the head:
Here is the gasket front side:
Back side:
Could it be possible the head is cracked in the port of the head where you can't see? But that would have no effect on the low compression reading I got.
Postmaster
Joined: Jun 2005
Posts: 2,656
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Thread Starter
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More Turbo
Joined: Oct 2004
Posts: 621
Likes: 2
From: Marana, AZ
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Hotshot
Joined: May 2004
Posts: 12,170
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From: The hills of No. Calif.
The discoloration on #7 cylinder is suspicious looking...
I tend to suspect a valve seating problem based on your compression readings. Clean the combustion chamber of #7 up with a wire brush and some carb cleaner, then lay the head so the chambers are flat, facing up. Fill the chamber with liquid (like rubbing alcohol) and see if it seeps past the valves. You could also shine a stong light into the ports and see if you can see any light around the valves.
Cleanup should also make it easier to see any potential cracks. I've seen them crack directly between the valves which is a small, hard-to-see crack.
I tend to suspect a valve seating problem based on your compression readings. Clean the combustion chamber of #7 up with a wire brush and some carb cleaner, then lay the head so the chambers are flat, facing up. Fill the chamber with liquid (like rubbing alcohol) and see if it seeps past the valves. You could also shine a stong light into the ports and see if you can see any light around the valves.
Cleanup should also make it easier to see any potential cracks. I've seen them crack directly between the valves which is a small, hard-to-see crack.
Senior User
Joined: Nov 2006
Posts: 310
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From: West Chester Pa.
The holes on the intake side of the gasket next to the bolt hole look small. The previous owner of my 91 F-250 spent a fortune paying a mechanic to trouble shoot a overheating problem. As it turned out it was the clutch in the clutch fan. It appeared to be working, but was just freewheeling. This will not solve your # 7 cylinder problem, but it wouldn't hurt to make sure it's working properly. You stick a rolled up news paper into the spinning fan. If it stops easily it's bad.
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More Turbo
Joined: Oct 2004
Posts: 621
Likes: 2
From: Marana, AZ
OK Dan, I cleaned it up and filled the port with lacquer thinner and it held nicely. I tried the exhaust port to no avail, it just came out the EGR passage on the other side. I did pour some down #8 exhaust port it was leaking around the valve a little. Its strange that the EGR only gets its flow from #7 and #3 cylinders??
Big Red- its not that type of overheating we are concerned with. This overheating is making the hoses hard as a rock even before it gets hot. The thermostat is opening as well.
Big Red- its not that type of overheating we are concerned with. This overheating is making the hoses hard as a rock even before it gets hot. The thermostat is opening as well.
Hotshot
Joined: May 2004
Posts: 12,170
Likes: 5
From: The hills of No. Calif.
Well, it's good to eliminate some potential sources of trouble. Try taking a strong light and looking closely in the gap between the piston and cylinder wall. You should have enough piston clearance to move it slightly to open the gap so you can see, working your way around the piston. Look for the piston ring end gap, and make sure you don't see more than one gap which would indicate a broken ring. Of course, you can only see the top ring...
I'm also wondering if you merely had the lifter preload too tight on that one cylinder. The compression had to be going somewhere...
I'm also wondering if you merely had the lifter preload too tight on that one cylinder. The compression had to be going somewhere...
Thread Starter
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More Turbo
Joined: Oct 2004
Posts: 621
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From: Marana, AZ
Thats whats baffeling me, I got all kinds of compression readings on that cylinder. The very first one was 75psi, so I thought maybe I didn't tighten up the hose to the cylinder very good, it was tight, and I did it again and I got like 10 psi then I got a 25 psi and then a 5psi and finally an 80 psi. So then I put about 1/2 teaspoon of oil in there and all I could get was 10 psi for the next 3 tries.
So let me ask you guys this, if the intake or exhaust valve was "slightly" bent could that cause it to sometimes seat and sometimes not? Its the only explaination I can come up with......
So let me ask you guys this, if the intake or exhaust valve was "slightly" bent could that cause it to sometimes seat and sometimes not? Its the only explaination I can come up with......