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Discussion Starter · #1 ·
I just bought a 1993 GMC C3500 with a 6.5 Turbo. I know NOTHING about 6.5s but I've always wanted one. This 6.5 has a cooling issue that I believe from my time wrenching is a head gasket. When I bought the truck it ran at 180, but the lower radiator hose was barely connected to the radiator (Just sitting on the fitting, not clamped.) I saw this and clamped it down properly, and like a switch, the truck hit 210 after not even 1 minute of running. The radiator cap became milky, the coolant was disappearing and the reservoir bubbled (only when shut off after running). I haven't done any in-depth diagnostics, these all seem like symptoms of a head gasket to me, but why would just tightening down a radiator hose show signs of headgasket failure? Shouldn't it show no matter what?
Please help me out, I've wanted this truck since I was 9.
 

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I just bought a 1993 GMC C3500 with a 6.5 Turbo. I know NOTHING about 6.5s but I've always wanted one. This 6.5 has a cooling issue that I believe from my time wrenching is a head gasket. When I bought the truck it ran at 180, but the lower radiator hose was barely connected to the radiator (Just sitting on the fitting, not clamped.) I saw this and clamped it down properly, and like a switch, the truck hit 210 after not even 1 minute of running. The radiator cap became milky, the coolant was disappearing and the reservoir bubbled (only when shut off after running). I haven't done any in-depth diagnostics, these all seem like symptoms of a head gasket to me, but why would just tightening down a radiator hose show signs of headgasket failure? Shouldn't it show no matter what?
Please help me out, I've wanted this truck since I was 9.
Welcome


People will bandaid things together just to get it sold/ran through auction, etc..
It sounds like they found a way to get the vehicle to pass an unsuspecting eye and now you're the bearer of a repair job..

200-210 is about the normal range. I would hook up a scanner and see what the computer sees for temps and also use an infrared temp gun to check things out.
The milky cap, bubbles in the coolant tank, and coolant loss is some of the signs.
I would go ahead and tear it down for inspection then start ordering needed parts ( ie, head gaskets, ARP studs, etc)

Ask lots of questions here, especially before buying parts, and post pics if you have troubles. The members here can get you through this.
Check the 6.5L FAQ page pinned at the top of this forum section for all the go-to information as well.
(y)
 

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Ronald Reagan fan
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The 6.5 isn’t a hard engine to disassemble and get back together.Pretty simple design and the parts aren’t expensive at all.Just remember to buy new head bolts if you decide to replace the head gaskets yourself.
 
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These engines have a propensity to crack between the valves, leaking combustion gas into the coolant passage and simulating a failed headgasket. A headgasket will obviously not fix that.

But you don't know until you get it apart.
 
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Discussion Starter · #5 ·
200-210 is about the normal range. I would hook up a scanner and see what the computer sees for temps and also use an infrared temp gun to check things out.
The milky cap, bubbles in the coolant tank, and coolant loss is some of the signs.
I would go ahead and tear it down for inspection then start ordering needed parts ( ie, head gaskets, ARP studs, etc)

Ask lots of questions here, especially before buying parts, and post pics if you have troubles. The members here can get you through this.
Check the 6.5L FAQ page pinned at the top of this forum section for all the go-to information as well.
(y)
I can't scan the truck because it's OBD1 so I/'' try the flash codes.
The Low coolant light has been on, even when I top it off it stays on.
If I had a bad head gasket wouldn't I look like Cheech and Chong with white smoke pouring out the exhaust? Or is that just a gas engine thing?
 

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Discussion Starter · #6 ·
The 6.5 isn’t a hard engine to disassemble and get back together.Pretty simple design and the parts aren’t expensive at all.Just remember to buy new head bolts if you decide to replace the head gaskets yourself.
I've been trying to educate myself on 6.5s through youtube and reading these forums. Is there a way I can test if it's a cracked head OR a gasket? If I do a gasket should I do a new head and valvetrain?
 

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Discussion Starter · #7 ·
These engines have a propensity to crack between the valves, leaking combustion gas into the coolant passage and simulating a failed headgasket. A headgasket will obviously not fix that.

But you don't know until you get it apart.
Would it be wise to replace the heads with the gaskets? Its at 289k miles
 

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I can't scan the truck because it's OBD1 so I/'' try the flash codes.
The Low coolant light has been on, even when I top it off it stays on.
If I had a bad head gasket wouldn't I look like Cheech and Chong with white smoke pouring out the exhaust? Or is that just a gas engine thing?
Excess smoke from the exhaust is another sign.
You don't need all the signs to confirm that it's a head gasket issue, just some of them..
The Milky cap, bubbles in the coolant tank and coolant loss are the indicators besides smoke.

When you tear it down have the heads inspected by a competent machine shop They will tell you if the heads are good for re-use or if they are needing to be replaced.
Don't just throw parts at it. You'll go broke quickly
 

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At a minimum it’s going to need new gaskets and bolts anyway.The heads do crack between the valves a lot.If you need new heads rockauto sells brand new bare head castings made by enginetech.Just a matter then of having a machine shop reuse your old valves and springs which is okay to do.
 

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At a minimum it’s going to need new gaskets and bolts anyway.The heads do crack between the valves a lot.If you need new heads rockauto sells brand new bare head castings made by enginetech.Just a matter then of having a machine shop reuse your old valves and springs which is okay to do.
NICE! And they claim to be domestic castings.
 

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NICE! And they claim to be domestic castings.
I’ve used their engine parts in the past with no issue.Seems to be great quality 👍
 

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Ronald Reagan fan
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I can't scan the truck because it's OBD1 so I/'' try the flash codes.
The Low coolant light has been on, even when I top it off it stays on.
If I had a bad head gasket wouldn't I look like Cheech and Chong with white smoke pouring out the exhaust? Or is that just a gas engine thing?
I came across one instance where a ford pickup was spewing white smoke quite badly.

I did some work on a 90s F350 with 5.8 gas engine for a fella I know and he wanted the head gaskets replaced.When I removed the valve covers I found two broken head bolts.Literally just the hex head of the bolts were broken laying inside the cylinder head.The owner wouldn’t get the heads checked so I cleaned them up and installed them with new gaskets and bolts.It smoked white like there was no tomorrow.Basically it must have had a cracked head or block but a bottle of block sealer made by gunk fixed it in order for the owner to sell it.

The distributor was seized solid.There was no moving it.I had to work around it….lol
 

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Discussion Starter · #13 ·
At a minimum it’s going to need new gaskets and bolts anyway.The heads do crack between the valves a lot.If you need new heads rockauto sells brand new bare head castings made by enginetech.Just a matter then of having a machine shop reuse your old valves and springs which is okay to do.
Would there be any reason to replace valves, springs, or rockers while I'm in there? I'd like to hop the truck up a little bit, so it can tow and accelerate better. Would refreshing the valvetrain help handle the extra go-go?
 

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New springs and rocker arms would be a good idea and if you buy the enginetech head castings the machine shop can resurface your current valves for you and install new valve stem seals.
 
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