GM 305 cleaning out... How should I proceed

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Ok so I have a 305 in my 22 year old GMC pickup truck. Overall the engine runs extremely well and only has 87,000 original miles. I plan on keeping it for a long time. I did the lower intake manifold gaskets recently and when I had the intake manifold off the valley of the block was sludged up. I think part of that issue was coolant was getting in there which was most likely contributing to the issue. I very carefully cleaned what I could but didn't mess with any of the larger chunks since I didn't want that clogging up the oil pump. I did an oil change with some semi synthetic castrol 5w30 and the lower end purolator filter with the plan to do an OCI at 500-1000 miles to get whatever gunk that was left over from the intake gasket replacement. When I had the valve covers off to change the gaskets, the top of the heads/rockers looked really good with minimal carbon deposits. I was actually impressed with how clean it looked after 22 years of unknown OCI's. Anyway I am wondering if I should do another very short OCI with cheap oil and filter or if i should get an oil that has more of cleaning detergents in there next (like PUP)
 
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Since the top end looked good and you cleaned what you could in the valley pan I would run maybe a 10w30 or 15w40 diesel oil as they have more detergents. You could use a full synthetic but I wouldn't want anything to aggressive. I would drive it 3k making sure it got good and hot maybe change the filter inbetween changes. Check the pcv system to. I ran a 5w40 euro synthetic in my 30 year old truck with a 302 and it stopped my filter up in about 500 miles. Funny thing is I also had the intake and valve covers off and it looked fine to me. Not sure if the oil was to blame but that truck never has a synthetic in it before until I did it.
 
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Cheap conventional oil like Super Tech 5W30 paired with a Super Tech filter and run it 1000 miles. Dont forget to treat your fuel system good also -- Chevron Techron Complete Fuel System Cleaner per instructions on bottle. wink
 
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Well, obviously you have no choice but to put a 383HT in it... grin2 Id run a couple of quick OCI 500-1000 miles with a high detergent oil and then call it good... Rotella is cheap, Delo is cheap, M1 HM is cheap with rebates...
 
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Jackson_Slugger

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I would use a cheap 5W-30 and Rislone for a full, but short, OCI of maybe 3K but keep an eye on it. The go with a quality syn on sale or with a rebate...
 
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I've had plenty of 305 chevy's in the past. They aren't picky at all. I always ran 5w-30 which was specified in the owners manual but plenty of people use 10w-30. I always used synthetic M1 back then. I'm sure today's conventional oils will be more than adequate at cleaning out your engine. I have a soft spot for 305 chevy's, the Chevy Caprice with the F41 suspension and performance axle definitely changed the whole feel of the car. The 305 wasn't well loved by the enthusiast community but I will say there is a stark difference between the carburetor vs fuel injected versions. The fuellys had decent performance, although someone looking to add more power was better off with a 350. The tuned port injection engines offered decent power but the TPI was finicky at times and long term not reliable. The throttle body versions were dead reliable and they still function to this day. The TBI engines didn't make as much power as the TPI but they still had more power than the carburetor ones. The later version 305 became part of the vortec family and they are pretty reliable too except for intake gasket failures and also fuel injection issues.
 

UncleDave

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If you are worried about it an interim low mile OCI/FCI with some delvac might clean a bit more (or " diesel oil" as previously mentioned) If the top end looked good I wouldnt bother if it were - and didnt when it was mine. As a gen Xer we got our licenses in the 80's and (at least my circles) drove really bad cars from the 70's. We got the 150 hp v8s no one wanted, 305's 318's on 2 barrels. Mine ground a lobe flat and I put an "RV" cam back in my 305 wagon and drove i all over the USA woke it up nicely. Towed a 23 t bucket using a VW tow bar from LA to Chicago and back across the Rockies - had plenty of snap even with a 3 speed. UD
 
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Originally Posted by buddylpal
I've had plenty of 305 chevy's in the past. They aren't picky at all. I always ran 5w-30 which was specified in the owners manual but plenty of people use 10w-30. I always used synthetic M1 back then. I'm sure today's conventional oils will be more than adequate at cleaning out your engine. I have a soft spot for 305 chevy's, the Chevy Caprice with the F41 suspension and performance axle definitely changed the whole feel of the car. The 305 wasn't well loved by the enthusiast community but I will say there is a stark difference between the carburetor vs fuel injected versions. The fuellys had decent performance, although someone looking to add more power was better off with a 350. The tuned port injection engines offered decent power but the TPI was finicky at times and long term not reliable. The throttle body versions were dead reliable and they still function to this day. The TBI engines didn't make as much power as the TPI but they still had more power than the carburetor ones. The later version 305 became part of the vortec family and they are pretty reliable too except for intake gasket failures and also fuel injection issues.
The early(mid to late 70's) had very soft blocks. The bores wore out quickly and caused oil burning. That is what started the dislike for them. A couple years ago I drove a 66 chevelle with a 305 and an edelbrock top end plus cam. Car had 3.31 gears and was very snappy and fun to drive. A 327 would have been even better.
 
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Originally Posted by Chris142
Originally Posted by buddylpal
I've had plenty of 305 chevy's in the past. They aren't picky at all. I always ran 5w-30 which was specified in the owners manual but plenty of people use 10w-30. I always used synthetic M1 back then. I'm sure today's conventional oils will be more than adequate at cleaning out your engine. I have a soft spot for 305 chevy's, the Chevy Caprice with the F41 suspension and performance axle definitely changed the whole feel of the car. The 305 wasn't well loved by the enthusiast community but I will say there is a stark difference between the carburetor vs fuel injected versions. The fuellys had decent performance, although someone looking to add more power was better off with a 350. The tuned port injection engines offered decent power but the TPI was finicky at times and long term not reliable. The throttle body versions were dead reliable and they still function to this day. The TBI engines didn't make as much power as the TPI but they still had more power than the carburetor ones. The later version 305 became part of the vortec family and they are pretty reliable too except for intake gasket failures and also fuel injection issues.
The early(mid to late 70's) had very soft blocks. The bores wore out quickly and caused oil burning. That is what started the dislike for them. A couple years ago I drove a 66 chevelle with a 305 and an edelbrock top end plus cam. Car had 3.31 gears and was very snappy and fun to drive. A 327 would have been even better.
Why would someone drop a 305 in a 66' Chevelle?
 
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Originally Posted by UncleDave
If you are worried about it an interim low mile OCI/FCI with some delvac might clean a bit more (or " diesel oil" as previously mentioned) If the top end looked good I wouldnt bother if it were - and didnt when it was mine. As a gen Xer we got our licenses in the 80's and (at least my circles) drove really bad cars from the 70's. We got the 150 hp v8s no one wanted, 305's 318's on 2 barrels. Mine ground a lobe flat and I put an "RV" cam back in my 305 wagon and drove i all over the USA woke it up nicely. Towed a 23 t bucket using a VW tow bar from LA to Chicago and back across the Rockies - had plenty of snap even with a 3 speed. UD
ANYDAY I would take a 318/5.2L over a 305 in the trucks back then. NOT EVEN comparable!!!! When the 305s were put in the Monte SS and Camaro I Roc Zs in 87 -- then the 305 was relevant.
 
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I had a 1990 Chevrolet Caprice, bought brand new from my dad, then he gave it to me. That 305 was the "non HO", so was 170 hp and 255 lbs of torque. Very durable and robust engine, very good fuel economy as well. Mine was the fuel injected 305. My father ran strictly a diet of Castrol GTX 5w30 or 10w30 for summer, and every two oil change after 100k km, he would add 1/2 a bottle of Wynns Stop Leak, even tho the engine was leaking no oil, as a preventive maintenance. I drove that car till it reached 385,000 km, no smoke, same oil usage since new, about 1/2 a quart every 5,000 km. Ran like brand new basically. Then we sold it to a guy, he drove it for another 150,000 km trouble free. I was young when I had it, beat the heck out of it, never had problems. So 500,000 ++++ km on regular oil. A good conventional should be fine.
 
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Originally Posted by wolf_06
I had a 1990 Chevrolet Caprice, bought brand new from my dad, then he gave it to me. That 305 was the "non HO", so was 170 hp and 255 lbs of torque. Very durable and robust engine, very good fuel economy as well. Mine was the fuel injected 305. My father ran strictly a diet of Castrol GTX 5w30 or 10w30 for summer, and every two oil change after 100k km, he would add 1/2 a bottle of Wynns Stop Leak, even tho the engine was leaking no oil, as a preventive maintenance. I drove that car till it reached 385,000 km, no smoke, same oil usage since new, about 1/2 a quart every 5,000 km. Ran like brand new basically. Then we sold it to a guy, he drove it for another 150,000 km trouble free. I was young when I had it, beat the heck out of it, never had problems. So 500,000 ++++ km on regular oil. A good conventional should be fine.
I got 535,000kms (335k miles) from my 89 Caprice. It ran like new still, smoothest engine I've had, but used some oil, didn't get great mileage anymore and the body and frame rusted out. My current one an 83 only has 240k miles. Runs good but has some piston slap when cold and needs valve seals (installing a catalyst got rid of the symptoms of that), uses very little oil.
 
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Originally Posted by caprice_2nv
Originally Posted by wolf_06
I had a 1990 Chevrolet Caprice, bought brand new from my dad, then he gave it to me. That 305 was the "non HO", so was 170 hp and 255 lbs of torque. Very durable and robust engine, very good fuel economy as well. Mine was the fuel injected 305. My father ran strictly a diet of Castrol GTX 5w30 or 10w30 for summer, and every two oil change after 100k km, he would add 1/2 a bottle of Wynns Stop Leak, even tho the engine was leaking no oil, as a preventive maintenance. I drove that car till it reached 385,000 km, no smoke, same oil usage since new, about 1/2 a quart every 5,000 km. Ran like brand new basically. Then we sold it to a guy, he drove it for another 150,000 km trouble free. I was young when I had it, beat the heck out of it, never had problems. So 500,000 ++++ km on regular oil. A good conventional should be fine.
I got 535,000kms (335k miles) from my 89 Caprice. It ran like new still, smoothest engine I've had, but used some oil, didn't get great mileage anymore and the body and frame rusted out. My current one an 83 only has 240k miles. Runs good but has some piston slap when cold and needs valve seals (installing a catalyst got rid of the symptoms of that), uses very little oil.
Yeah my dad had an 84, piston slap since new, never had a problem, just a slap. I cant remember if he had it fixed or not. I think it was on cold startup.
 

luca

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I will stick with the cheap oil and filter and low mileage OCI's. thanks! BTW - Not looking to hot rod anything. It's just my Home Depot truck. It runs great as is and I am happy with it. I did upgrade the fuel injection module to the MPFI unit which made a big difference.
 
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Originally Posted by Chris142
Originally Posted by BAJA_05
Cheap conventional oil like Super Tech 5W30 paired with a Super Tech filter and run it 1000 miles;)
x2. Warren makes great oils. The 305 was known for it's v8 fuel economy with v6 performance!
Most of my 305s have gotten V6 fuel economy (25mpg+) but yes they were V6 performance. Except the 86+87 models I had, they would roast the tires. Better than v6s of that time anyway.
 
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Originally Posted by wolf_06
Originally Posted by caprice_2nv
Originally Posted by wolf_06
I had a 1990 Chevrolet Caprice, bought brand new from my dad, then he gave it to me. That 305 was the "non HO", so was 170 hp and 255 lbs of torque. Very durable and robust engine, very good fuel economy as well. Mine was the fuel injected 305. My father ran strictly a diet of Castrol GTX 5w30 or 10w30 for summer, and every two oil change after 100k km, he would add 1/2 a bottle of Wynns Stop Leak, even tho the engine was leaking no oil, as a preventive maintenance. I drove that car till it reached 385,000 km, no smoke, same oil usage since new, about 1/2 a quart every 5,000 km. Ran like brand new basically. Then we sold it to a guy, he drove it for another 150,000 km trouble free. I was young when I had it, beat the heck out of it, never had problems. So 500,000 ++++ km on regular oil. A good conventional should be fine.
I got 535,000kms (335k miles) from my 89 Caprice. It ran like new still, smoothest engine I've had, but used some oil, didn't get great mileage anymore and the body and frame rusted out. My current one an 83 only has 240k miles. Runs good but has some piston slap when cold and needs valve seals (installing a catalyst got rid of the symptoms of that), uses very little oil.
Yeah my dad had an 84, piston slap since new, never had a problem, just a slap. I cant remember if he had it fixed or not. I think it was on cold startup.
I think my piston slap started after I let my ex drive it to work a few times in the winter when she swore there was something wrong with her Saturn. She later admitted she made it up because she liked driving my car. I think she might have been hot rodding it when it was still cold. This time of year you can't hear it, just on cold start in the winter. The high mileage 89 never had a peep out of the engine though.
 
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Originally Posted by buddylpal
I've had plenty of 305 chevy's in the past. They aren't picky at all. I always ran 5w-30 which was specified in the owners manual but plenty of people use 10w-30. I always used synthetic M1 back then. I'm sure today's conventional oils will be more than adequate at cleaning out your engine. I have a soft spot for 305 chevy's, the Chevy Caprice with the F41 suspension and performance axle definitely changed the whole feel of the car. The 305 wasn't well loved by the enthusiast community but I will say there is a stark difference between the carburetor vs fuel injected versions. The fuellys had decent performance, although someone looking to add more power was better off with a 350. The tuned port injection engines offered decent power but the TPI was finicky at times and long term not reliable. The throttle body versions were dead reliable and they still function to this day. The TBI engines didn't make as much power as the TPI but they still had more power than the carburetor ones. The later version 305 became part of the vortec family and they are pretty reliable too except for intake gasket failures and also fuel injection issues.
I don't agree with the TBI having more power than the lg4 305s, at least compared to higher compression 9.5:1 85-88 version. My 86 that got wrote off and my 86 parts car with only 110k miles will roast the tires off. My 83 with 8.5:1 Cr is a lot slower but still faster than my TBI 89 (I also had a second one for parts with only 230k miles and it drove the same as the 335k mile one). The swirl port heads on the l03 engine were pretty lame, nothing like the tuned port injection or vortec 305s. The TBI was probably the most reliable other than having to do an intake manifold gasket once in its lifetime. They are aluminum intake, the older carbed ones like my 83 are cast iron and never seem to leak. The worst thing about the 305 is valve seals and valve cover gaskets will leak, and even if you fix it, they will leak again within 10 years. My Olds 350 hasn't had any leakage problems.
 
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Originally Posted by Chris142
Originally Posted by BAJA_05
Cheap conventional oil like Super Tech 5W30 paired with a Super Tech filter and run it 1000 miles;)
x2. Warren makes great oils. The 305 was known for it's v8 fuel economy with v6 performance!
That's when they weren't eating cams, losing valve seals, and basically being the gutless turd of the SBC family!
 
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Originally Posted by skyactiv
Originally Posted by Chris142
Originally Posted by buddylpal
I've had plenty of 305 chevy's in the past. They aren't picky at all. I always ran 5w-30 which was specified in the owners manual but plenty of people use 10w-30. I always used synthetic M1 back then. I'm sure today's conventional oils will be more than adequate at cleaning out your engine. I have a soft spot for 305 chevy's, the Chevy Caprice with the F41 suspension and performance axle definitely changed the whole feel of the car. The 305 wasn't well loved by the enthusiast community but I will say there is a stark difference between the carburetor vs fuel injected versions. The fuellys had decent performance, although someone looking to add more power was better off with a 350. The tuned port injection engines offered decent power but the TPI was finicky at times and long term not reliable. The throttle body versions were dead reliable and they still function to this day. The TBI engines didn't make as much power as the TPI but they still had more power than the carburetor ones. The later version 305 became part of the vortec family and they are pretty reliable too except for intake gasket failures and also fuel injection issues.
The early(mid to late 70's) had very soft blocks. The bores wore out quickly and caused oil burning. That is what started the dislike for them. A couple years ago I drove a 66 chevelle with a 305 and an edelbrock top end plus cam. Car had 3.31 gears and was very snappy and fun to drive. A 327 would have been even better.
Why would someone drop a 305 in a 66' Chevelle?
Originally a 6-cyl car? They had a running engine I guess.
 
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