L98 head gasket question
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
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From: Port Costa CA
L98 head gasket question
Hey guys finally got the energy to tackle a blown head gasket on my 1988 L98 engine.
After a bat to get the heads off removing the old head gaskets I noticed the water jacket holes in the block and Alum, cylinder heads were about the size between a quarter and a nickel however the OEM gasket and my new Felpro set have holes about the size of a pencil.
Seems to me this small gasket hole would restrict water flow through the heads thus causing overheating?
I am considering punching out these gasket holes to fit the head and block is that a mistake?
Why would the gaskets holes be so small?
After a bat to get the heads off removing the old head gaskets I noticed the water jacket holes in the block and Alum, cylinder heads were about the size between a quarter and a nickel however the OEM gasket and my new Felpro set have holes about the size of a pencil.
Seems to me this small gasket hole would restrict water flow through the heads thus causing overheating?
I am considering punching out these gasket holes to fit the head and block is that a mistake?
Why would the gaskets holes be so small?
Pro
Joined: Jan 2003
Posts: 706
Likes: 47
From: Denver Colorado
I believe you have the correct size holes. The flows thru the head are restricted to a degree. The coolant must be in contact with the metal to pick up the heat. Too fast flow reduces the amount of heat transfer to the coolant. If you have the correct part number gasket and it matches the OEM one you are removing you will be OK. 
Oil Producer
Joined: Apr 2014
Posts: 9,375
Likes: 2,737
I believe you have the correct size holes. The flows thru the head are restricted to a degree. The coolant must be in contact with the metal to pick up the heat. Too fast flow reduces the amount of heat transfer to the coolant. If you have the correct part number gasket and it matches the OEM one you are removing you will be OK.
what head gasket are you ordering to replace your 88?
Melting Slicks
Joined: Nov 2010
Posts: 2,216
Likes: 113
From: Michigan
The hole sizes are by design and meant to direct/even flow to the needed areas. Some race gaskets will have different size holes to try even more to correct bad cooling spots. Holes can be oversized in castings/block to get the sand out.
Last edited by BOOT77; Jan 10, 2016 at 05:19 AM.
Race Director
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I do somewhat understand the effectiveness of coolant vs flow (or the myth), but FWIW....
I've read that most aluminum head L98's have head gasket issues at either #7 or #8 cylinders. this happens to be at the same location as the restrictors. along with the restrictors, GM installed a STEAM tube on the intake with the aluminum heads. I don't know about you guys, but the word STEAM scares the crap out of me, especially with creating steam from antifreeze. I have read that several members have installed non-restrictor manifold gaskets without issues. on my 90, I installed manifold gaskets from an iron head L98 (fel-pro, open rear ports). it's been two years now (about 6-7K miles), and I haven't noticed any temperature problems. it's running fine - performance, engine temps - everything seems normal even with the hot florida summers. BTW, running a 180 degree stat. just my 2-cents -
I've read that most aluminum head L98's have head gasket issues at either #7 or #8 cylinders. this happens to be at the same location as the restrictors. along with the restrictors, GM installed a STEAM tube on the intake with the aluminum heads. I don't know about you guys, but the word STEAM scares the crap out of me, especially with creating steam from antifreeze. I have read that several members have installed non-restrictor manifold gaskets without issues. on my 90, I installed manifold gaskets from an iron head L98 (fel-pro, open rear ports). it's been two years now (about 6-7K miles), and I haven't noticed any temperature problems. it's running fine - performance, engine temps - everything seems normal even with the hot florida summers. BTW, running a 180 degree stat. just my 2-cents -
Last edited by Joe C; Jan 10, 2016 at 06:58 AM.
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
Likes: 2
From: Port Costa CA
L98 head gasket question
I do somewhat understand the effectiveness of coolant vs flow (or the myth), but FWIW....
I've read that most aluminum head L98's have head gasket issues at either #7 or #8 cylinders. this happens to be at the same location as the restrictors. along with the restrictors, GM installed a STEAM tube on the intake with the aluminum heads. I don't know about you guys, but the word STEAM scares the crap out of me, especially with creating steam from antifreeze. I have read that several members have installed non-restrictor manifold gaskets without issues. on my 90, I installed manifold gaskets from an iron head L98 (fel-pro, open rear ports). it's been two years now (about 6-7K miles), and I haven't noticed any temperature problems. it's running fine - performance, engine temps - everything seems normal even with the hot florida summers. BTW, running a 180 degree stat. just my 2-cents -
I've read that most aluminum head L98's have head gasket issues at either #7 or #8 cylinders. this happens to be at the same location as the restrictors. along with the restrictors, GM installed a STEAM tube on the intake with the aluminum heads. I don't know about you guys, but the word STEAM scares the crap out of me, especially with creating steam from antifreeze. I have read that several members have installed non-restrictor manifold gaskets without issues. on my 90, I installed manifold gaskets from an iron head L98 (fel-pro, open rear ports). it's been two years now (about 6-7K miles), and I haven't noticed any temperature problems. it's running fine - performance, engine temps - everything seems normal even with the hot florida summers. BTW, running a 180 degree stat. just my 2-cents -
It did appear the problem cylinders were #7 and #8 as Joe C. had said.
So I still am in a quagmire whether opening the new head gasket holes a little or enough to match the block would do any harm?
Boot77 mentioned over sizing holes in the castings/blocks but how about just the head gasket? what could be the harm?
They are the correct gasket Felpro set from my Actual auto parts store not O'rieily , they actually know about cars.
To answer Vikingtrad3R, the Felpro set covers 86 to 91 , 5.7 l, engines # HS-7733 PT-9
So bottom line? any harm in opening the coolant holes in the new head gaskets a small amount???
1984Z51auto I guess what you say makes sense but do you think there would be any harm in say just doubling the hole size? As I said the blocks holes are slightly smaller than a quarter and the head gast is about the size of a pencil, big difference as Joe C said he used head gaskets for the iron heads and has had no problems for 7K miles.?
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 764
To start with thanks to all, to answer some of your questions the OEM head gasket was the same as the new set of Felpro head gaskets.
It did appear the problem cylinders were #7 and #8 as Joe C. had said.
So I still am in a quagmire whether opening the new head gasket holes a little or enough to match the block would do any harm?
Boot77 mentioned over sizing holes in the castings/blocks but how about just the head gasket? what could be the harm?
They are the correct gasket Felpro set from my Actual auto parts store not O'rieily , they actually know about cars.
To answer Vikingtrad3R, the Felpro set covers 86 to 91 , 5.7 l, engines # HS-7733 PT-9
So bottom line? any harm in opening the coolant holes in the new head gaskets a small amount???
1984Z51auto I guess what you say makes sense but do you think there would be any harm in say just doubling the hole size? As I said the blocks holes are slightly smaller than a quarter and the head gast is about the size of a pencil, big difference as Joe C said he used head gaskets for the iron heads and has had no problems for 7K miles.?
It did appear the problem cylinders were #7 and #8 as Joe C. had said.
So I still am in a quagmire whether opening the new head gasket holes a little or enough to match the block would do any harm?
Boot77 mentioned over sizing holes in the castings/blocks but how about just the head gasket? what could be the harm?
They are the correct gasket Felpro set from my Actual auto parts store not O'rieily , they actually know about cars.
To answer Vikingtrad3R, the Felpro set covers 86 to 91 , 5.7 l, engines # HS-7733 PT-9
So bottom line? any harm in opening the coolant holes in the new head gaskets a small amount???
1984Z51auto I guess what you say makes sense but do you think there would be any harm in say just doubling the hole size? As I said the blocks holes are slightly smaller than a quarter and the head gast is about the size of a pencil, big difference as Joe C said he used head gaskets for the iron heads and has had no problems for 7K miles.?
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i would think the reason that some gasket holes are smaller is to increase flow pressure through those holes.
I would think that if all holes were the same size for example, there would be regions within the cooling jacket that would never be allowed to flow out towards the rad.
Im no expert and this is just brainstorming but i would think thw front of the block would circulate nicely, but the rear may not.
unless the cooling jacket is like a guided river passageway that flows theough a circuitous pathway theough the hole block. my impression is that its not though.
So i could see why, based on flow dynamics, the gaskets may be designed with restricted ports on the gaskets to increase pressure through that hole purely to ensure that the coolant trying to travel through that coolant pssage actually flows as opposed to being bavkpressured by some larger faster moving coolant.
So, id want to understand the engineering behind the restricted holes, clearly intentional, before changing them. Ironically, you could reduce flow theough a hole if it is a low pressure zone in the coolant jacket by opening the holes up in the gasket.
just thinking outloud.
I would think that if all holes were the same size for example, there would be regions within the cooling jacket that would never be allowed to flow out towards the rad.
Im no expert and this is just brainstorming but i would think thw front of the block would circulate nicely, but the rear may not.
unless the cooling jacket is like a guided river passageway that flows theough a circuitous pathway theough the hole block. my impression is that its not though.
So i could see why, based on flow dynamics, the gaskets may be designed with restricted ports on the gaskets to increase pressure through that hole purely to ensure that the coolant trying to travel through that coolant pssage actually flows as opposed to being bavkpressured by some larger faster moving coolant.
So, id want to understand the engineering behind the restricted holes, clearly intentional, before changing them. Ironically, you could reduce flow theough a hole if it is a low pressure zone in the coolant jacket by opening the holes up in the gasket.
just thinking outloud.
To start with thanks to all, to answer some of your questions the OEM head gasket was the same as the new set of Felpro head gaskets.
It did appear the problem cylinders were #7 and #8 as Joe C. had said.
So I still am in a quagmire whether opening the new head gasket holes a little or enough to match the block would do any harm?
Boot77 mentioned over sizing holes in the castings/blocks but how about just the head gasket? what could be the harm?
They are the correct gasket Felpro set from my Actual auto parts store not O'rieily , they actually know about cars.
To answer Vikingtrad3R, the Felpro set covers 86 to 91 , 5.7 l, engines # HS-7733 PT-9
So bottom line? any harm in opening the coolant holes in the new head gaskets a small amount???
1984Z51auto I guess what you say makes sense but do you think there would be any harm in say just doubling the hole size? As I said the blocks holes are slightly smaller than a quarter and the head gast is about the size of a pencil, big difference as Joe C said he used head gaskets for the iron heads and has had no problems for 7K miles.?
It did appear the problem cylinders were #7 and #8 as Joe C. had said.
So I still am in a quagmire whether opening the new head gasket holes a little or enough to match the block would do any harm?
Boot77 mentioned over sizing holes in the castings/blocks but how about just the head gasket? what could be the harm?
They are the correct gasket Felpro set from my Actual auto parts store not O'rieily , they actually know about cars.
To answer Vikingtrad3R, the Felpro set covers 86 to 91 , 5.7 l, engines # HS-7733 PT-9
So bottom line? any harm in opening the coolant holes in the new head gaskets a small amount???
1984Z51auto I guess what you say makes sense but do you think there would be any harm in say just doubling the hole size? As I said the blocks holes are slightly smaller than a quarter and the head gast is about the size of a pencil, big difference as Joe C said he used head gaskets for the iron heads and has had no problems for 7K miles.?
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
Likes: 2
From: Port Costa CA
L98 head gasket question
i would think the reason that some gasket holes are smaller is to increase flow pressure through those holes.
I would think that if all holes were the same size for example, there would be regions within the cooling jacket that would never be allowed to flow out towards the rad.
Im no expert and this is just brainstorming but i would think thw front of the block would circulate nicely, but the rear may not.
unless the cooling jacket is like a guided river passageway that flows theough a circuitous pathway theough the hole block. my impression is that its not though.
So i could see why, based on flow dynamics, the gaskets may be designed with restricted ports on the gaskets to increase pressure through that hole purely to ensure that the coolant trying to travel through that coolant pssage actually flows as opposed to being bavkpressured by some larger faster moving coolant.
So, id want to understand the engineering behind the restricted holes, clearly intentional, before changing them. Ironically, you could reduce flow theough a hole if it is a low pressure zone in the coolant jacket by opening the holes up in the gasket.
just thinking outloud.
I would think that if all holes were the same size for example, there would be regions within the cooling jacket that would never be allowed to flow out towards the rad.
Im no expert and this is just brainstorming but i would think thw front of the block would circulate nicely, but the rear may not.
unless the cooling jacket is like a guided river passageway that flows theough a circuitous pathway theough the hole block. my impression is that its not though.
So i could see why, based on flow dynamics, the gaskets may be designed with restricted ports on the gaskets to increase pressure through that hole purely to ensure that the coolant trying to travel through that coolant pssage actually flows as opposed to being bavkpressured by some larger faster moving coolant.
So, id want to understand the engineering behind the restricted holes, clearly intentional, before changing them. Ironically, you could reduce flow theough a hole if it is a low pressure zone in the coolant jacket by opening the holes up in the gasket.
just thinking outloud.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The coolant flow starts at the water pump, which is attached to the block. The coolant flows toward the back of the block around the cylinders. Some coolant gets bypassed through those small holes into the heads. The flow in the heads is generally from the rear towards the front. The coolant goes from the heads into the intake manifold and then to the thermostat and then to the radiator.
Thread Starter
Instructor
Joined: Jan 2015
Posts: 203
Likes: 2
From: Port Costa CA
L98 head gasket question
The coolant flow starts at the water pump, which is attached to the block. The coolant flows toward the back of the block around the cylinders. Some coolant gets bypassed through those small holes into the heads. The flow in the heads is generally from the rear towards the front. The coolant goes from the heads into the intake manifold and then to the thermostat and then to the radiator.
What are your thoughts on enlarging the head gasket coolant holes to the heads even a small amount?