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 Page 1 of 3 123
Username Post: 400 sbc--overheating myth?        (Topic#173832)
clyde 
Member
Posts: 82

Reg: 10-20-05
11-03-07 04:41 PM - Post#1287849    

Are 400 small blocks more prone to overheating than other small block or is this just urban legend? What if they are bored .30 over? I know there are a lot of variables that could come into play but it seems that the word 400 and overheating are used in the same sentence a lot. Anyone have any long term experience with this engine? Thanks
http://s197.photobucket.com/albums/aa193/2drsedan m...


 
stricker76 
Frequent Contributor
Posts: 2370
stricker76
Loc: Ontario, Canada
Reg: 05-17-06
11-03-07 04:45 PM - Post#1287851    
    In response to clyde

I have a 400 in my chevelle that is 60 over and have never had any problems. I am using a heavier 3 core maxi-fin rad out of a mid 80's silverado, and it has never went over about 190 and that was on an overly hot day.
2007 Avalanche LT
1998 C2500 Reg cab 6.5L
1973 Monte Carlo - On the chopping block
1995 C1500 - R.I.P

http://www.cardomain.com/id/stricker76


 
RickWI 
Very Senior Member
Posts: 1669

Loc: Madison, WI
Reg: 10-08-01
11-03-07 05:01 PM - Post#1287862    
    In response to stricker76

Since the 70's. Myth
70 SS Camaro, Dart Aluminum SmBlk 454 CI, 125 MPH (on the motor) in the quarter and 18 MPG on Power Tour


 
craigblock 
Valued Contributor
Posts: 4008
craigblock
Loc: Ottawa
Reg: 05-22-05
11-03-07 05:05 PM - Post#1287865    
    In response to RickWI

While we're here, what about:

"400s are more crack prone"
or
"A 4 bolt 400 is not as strong as a 2 bolt 400"
Casting Numbers


 
RickWI 
Very Senior Member
Posts: 1669

Loc: Madison, WI
Reg: 10-08-01
11-03-07 05:19 PM - Post#1287871    
    In response to craigblock

I do not see them as being any more "crack prone"

Both a 4 and 2 bolt are plenty strong for most applications of the hobby guy. We take 2 bolt blocks and convert to splayed 4 bolt steel mains for Late Model competition engine applications.
70 SS Camaro, Dart Aluminum SmBlk 454 CI, 125 MPH (on the motor) in the quarter and 18 MPG on Power Tour


 
Stinky 
Senior Member
Posts: 1232

Loc: Whitewater, CO
Reg: 05-25-01
11-03-07 05:40 PM - Post#1287884    
    In response to RickWI

If used to tow, or driven hard, where it gets hot, like AZ...they are a poj (junk) and it is believed to be a truth there as the seem to have a higher failure rate than a 350.

 
Doorslammer 
Senior Member
Posts: 304

Loc: Central Florida
Reg: 02-07-03
11-04-07 07:34 AM - Post#1288157    
    In response to clyde

400 or prone to over heating if you don't have the steam holes drilled in the heads !
but then again you can say you have the wrong heads on LOL
anyway I had a 406 in full race trim with solid roller & tunnel ram & never had a problem
1981 shortbed 355ci. 373 posi,NOS 100hp shot 13.39 @ 101mph 2.141-60foot 4300lb heavy


 
Mike 
Senior Member
Posts: 8136

Reg: 06-30-00
11-04-07 08:32 AM - Post#1288202    
    In response to clyde

Some/much of that comes from the heads cracking due to the thin castings used during that period.
Wasn't just the 400's either.

 
Brakedust 
Very Senior Member
Posts: 1549

Loc: Frozen tundra
Reg: 10-25-00
11-04-07 08:37 AM - Post#1288208    
    In response to clyde

  • Quote:
it seems that the word 400 and overheating are used in the same sentence a lot



It may qualify as an urban legend of some sorts in the automotive world. My take on it that the 400s that did overheat were in stock form and were beat on and not taken care of very well. The rumor probably started back in the 1970s when Cletus' 400 powered tow truck (which probably didn't have the proper cooling system that a tow truck should have) began to overheat when towing a real heavy load and he got mad and said that all 400s overheat. The rumor spread by word of mouth and 30 some years later you still have some people believing it! If you build it to overheat it will. If you build it so it doesn't, it won't.

Speaking from my own personal experience my 400 had a baby blower on it and was built accordingly. I had a Be Cool aluminum radiator and electric fan and even with the extra heat from the blower I never went over 190 degrees even with my foot in it.

Edited by Big_10 on 11-04-07 08:46 AM. Reason for edit: No reason given.

 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15695

Loc: Colorado Springs, CO
Reg: 08-08-04
11-04-07 08:48 AM - Post#1288215    
    In response to Mike

400's have siamesed bores. Consequently, in order to eliminate steam pockets created by the siamesed bores, the 400's HAD TO be drilled for steam holes, and so did the heads.

It's reputation came from people pulling the motor apart and swapping in different parts (like heads that haven't been drilled for steam holes) or using the incorrect gaskets (that covered up the steam holes).

Assembled properly with good parts, the 400 has no particular affinity for overheating.

As Mike said, the heads during that time period were very thin in some areas - which is what lead to a lot of 400s needing a top end rebuild. Once the top end was removed, people switched in different heads that were less prone to cracking. But, since they were unfamiliar with what had to be done to assemble it properly (gasket and head drilling) - the motors started overheating immediately. Most owners at that point threw up their hands and replaced the motor with a 350, or sold the vehicle. That is why it has such a reputation for overheating.

 
scottm 
Member
Posts: 73

Loc: Scottsdale, AZ
Reg: 03-13-05
11-04-07 09:27 AM - Post#1288237    
    In response to Vaughn

I think there was some truth to it. I worked in a machine shop in Tempe AZ in the early 80's. I saw lots of cracked 400 blocks and heads. But in most every case, the steam holes were clogged with rust. In the late 70's people didnt pay much attention to maintenance and proper coolant. If you filled your radiator with straight tap water, rust flakes will clog up the steam holes on the 400. This can cause cracking of the thin 400 heads. But with a healthy radiator and good coolant mixed with purified water, there is no problem at all with overheating, even with stock heads.
I spend most of my money on beer, women and racing. The rest I just waste.

77 C10 Class 8 desert race 520hp sb372/mvb th400, 82 Titan RV 454/th400, 93 Blazer 350/5sp, 94 Blazer 6.5 diesel/4l80, 94 C2500 6.5 diesel/nv4500, 97 K3500 454/4l80


 
greg_moreira 
Very Senior Member
Posts: 3264

Reg: 10-06-03
11-04-07 04:44 PM - Post#1288527    
    In response to scottm

I wouldnt say 400's are "prone" to overheating, but rather...a stout 400 will exploit a "less than capable" cooling system. You can keep these motors cool....but they need a descent cooling system. It may not survive as well as a warmed over 350 would with an average cooling system. So by comparison, I suppose thats where the rumor could have come from.

Guys building these engines, swapping heads, and not knowing they are supposed to drill steam holes may have aided to some of the rumors as well. Im sure that happened plenty of times back in the day before this info was readily known/avalable like it is today. And problems were probably a little more common mostly because things werent done right.

And yeah. The 2 bolt block is more preferred. The 509 cast especially.

 
fritz1990 
Dedicated Enthusiast
Posts: 6411
fritz1990
Age: 53
Loc: Kansas
Reg: 02-16-03
11-04-07 05:26 PM - Post#1288565    
    In response to greg_moreira

I had a 406 solid lifter in my '77 Corvette with ported 350 heads but I drilled the steam holes and never had a problem with it A/C on or off. I used to build circle track engines for some locals some years ago and never ran any hotter than the 350's they replaced. They ran 406's and 377's with 350 and 327 heads but I drilled holes in them also. I have a 4 bolt std bore 400 sittin' around now that I will turn into a 377 when I find the right home for it. I almost put it in my '65 as a 406 but wanted a BBC instead, good move on me!

Regards, Jeff
1998 K1500 6.5 Coal burner
1965 C10 with 498 BBC AFR Heads
1964 C10 Ran 348W for 6 years, now SBC.

Corvettes owned: '74 '77 '78 L82 Silver Anniversary, 2002 LS1

Don't have a nervous come together!

http://picasaweb.google.com/fritz199090


 
scrambldcj8 
Senior Member
Posts: 1770

Loc: MA
Reg: 04-06-03
11-04-07 06:26 PM - Post#1288624    
    In response to scottm

  • scottm Said:
I think there was some truth to it. I worked in a machine shop in Tempe AZ in the early 80's. I saw lots of cracked 400 blocks and heads. But in most every case, the steam holes were clogged with rust. In the late 70's people didnt pay much attention to maintenance and proper coolant. If you filled your radiator with straight tap water, rust flakes will clog up the steam holes on the 400. This can cause cracking of the thin 400 heads. But with a healthy radiator and good coolant mixed with purified water, there is no problem at all with overheating, even with stock heads.




WINNER! The above post IMO hit the nail on the head. It comes down to two major points...poor maintenance causing the steam holes to clog up and #2 some people did head swaps and failed to drill the proper steam holes.

IMO, they are only more prone to overheating only because they may have been more sensitive to neglect.

 
1983G20Van 
Super Senior Member
Posts: 3223

Loc: Bedford, Texas, USA
Reg: 11-13-02
11-04-07 07:28 PM - Post#1288677    
    In response to scrambldcj8

The overheating issue on a well maintained 400 small block or even a built 400 small block is FALSE. Sure a built 400 will overheat if you try to use the stock 230 I6 radiator, a flex fan, and no shroud to cool it.

Finally onto the 2 bolt vs. 4 bolt main thing.

The 2 bolt main block IS STRONGER than the 4 bolt. The main caps on a 4 bolt 400 are known to crack at times when subjected to stress. The reason is due to the thickness between the bolt platforms. They get VERY thin between the innner and outer bolt platforms. This is due to the larger main bearing journals in the 400.
1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 
Rick_L 
Honored Member
Posts: 25838

Loc: Katy, Tx, USA
Reg: 07-06-00
11-05-07 01:36 PM - Post#1289178    
    In response to 1983G20Van

My take - 400s are prone to having trouble after overheating occurs repeatedly.

The distributor timing that an original 400 had was not very friendly to controlling water temperature, especially at idle and cruise rpm's.

And as others have mentioned, the heads on them were prone to cracking - but part of this comes back to the timing causing overheating.

 
74LagunaS3 
Valued Contributor
Posts: 3783
74LagunaS3
Loc: Winchester, MA , USA. H...
Reg: 02-23-00
11-07-07 10:19 AM - Post#1290671    
    In response to Rick_L

"Overheating"

Mostly due to the original configuration of the 400 was probably a valid complaint.

The 400 was a truck only option from 77-80 usually with a 2bbl carb in applications which really called for a 454

Even the cars that got the 400 were heavy, 70-73 Caprice/Impala only. 74-76 Chevelles also got em

The later 74 400's even had the early release HEI

The lightweight head castings were phased in during this time such as the 882

The horrible Cat converter in 75 overheated many a motor after they were clogged.

One crack point is between the steam hole and head bolt, not much material between and no other small block has steam holes


74 Laguna S3 Project

2004 Merc Marauder driver


Edited by 74LagunaS3 on 11-07-07 10:21 AM. Reason for edit: No reason given.

 
Rich 5150 69 
Frequent Contributor
Posts: 1939
Rich 5150 69
Loc: Sac, Calif
Reg: 11-21-04
10-22-09 10:44 PM - Post#1792897    
    In response to 74LagunaS3

I have a 400 in my `37 coupe with only a electric fan pusher, not enough room for a mechanical, on the road it runs at 180 degrees with a 180 thermostat, at the stop light it runs at 205.
`64 Chevy sb, `69 RS/SS, `37 F**d Coupe 406 sm blk
http://photobucket.com/R51506964


 
World Domination 
Contributor
Posts: 506

Reg: 03-01-08
10-26-09 01:56 PM - Post#1794782    
    In response to Rich 5150 69

Why didn't the factory drill these "steam holes?"

 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15695

Loc: Colorado Springs, CO
Reg: 08-08-04
10-26-09 07:08 PM - Post#1794979    
    In response to World Domination

The factory did drill steam holes - in the heads intended to be put on 400 blocks - but not on any other heads.

When someone swaps the heads out to "better" ones, the new heads may or may not be drilled for the steam holes (usually not). The rest of ALL sbc heads (283 up through 350) do not have steam holes, because they do not have the 400 blocks siamesed bores.

If you want to swap any sbc head onto a 400, you have to drill steam holes, otherwise a 400 WILL overheat.

 
fcompoccio 
Forum Newbie
Posts: 37

Reg: 08-23-11
08-23-11 11:48 AM - Post#2129242    
    In response to Vaughn

I'm about to lose it. A couple of years ago I bought a 400 small block from an engine manufacturer in Washington state. Installed it in my 66 Impala with tri-power and a 350 Trans.

This car has been forever running very hot. I've done everything including recently installing an alumuminum large radiator with 2 electric fans. Everything is new and run antifreeze and coolant only no water and no thermostat. I think the steam hole theory maybe it. But what the hell are steam holes? I was a professional mechanic many years ago and worked on many small block chevys so I know a thing or two. But can someone tell me what to do and I'll have my friend who owns a shop pull the heads and do this steam hole thing. I don't know what else to do. Can someone take me through this in Baby steps?
Thanks in advance
Frank

 
D.Mac 
Senior Member
Posts: 999

Loc: Ontario Canada
Reg: 03-22-03
08-23-11 12:37 PM - Post#2129262    
    In response to fcompoccio

No thermostat?????
Dave MacDonald
Ontario, Canada

'66 Impala LT1/C950-,EFI,700R4,(sold 07/2011)
'12 Sonic LTZ, Turbo, M6
'07 Pontiac Solstice GXP
'06 Caddy CTS-V


 
IgnitionMan 
Valued Contributor
Posts: 2713

Reg: 04-15-05
08-23-11 03:52 PM - Post#2129355    
    In response to fcompoccio

Well, there's one of the problems right there, electric fans designed for 210 to 230 degrees/F. emissions engine temps. After all that a lot of us have posted, there are still people that seem to not believe what does work, and blindly believe what manufacturers say, that doesn't work. Proves that people aren't stupid, just that over hype and really bad advice advertising WORKS too good.

 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15695

Loc: Colorado Springs, CO
Reg: 08-08-04
08-23-11 03:56 PM - Post#2129364    
    In response to D.Mac

Well, you have to run 50/50 water/coolant MAXIMUM - and you have to run a thermostat.

There is no benefit to running 100 percent coolant, because the water is the cooling medium - not the coolant (despite its name). Antifreeze's primary use is to extend the amount of heat the WATER can absorb and decrease it's freezing point, in addition to keeping the water jacket from rusting up or leaching aluminum out of the block/heads. Water does all the cooling.

The second gigantic mistake is not running a thermostat. A thermostat allows water pressure to build in the block - which increases water's boiling point, forcing water to absorb more heat. If you run without a thermostat, no pressure will build in your cooling system - so I can absolutely guarantee that your motor will overheat without one.

Removing the thermostat from a cooling system is one of those tricks that the drag racing community used (or used to use) to keep the block as cool as possible - which only worked because of the very short time that a racing motor would run. It should NEVER be used on a street driven vehicle. It was a trick that less-knowledgeable people unfortunately used on the street because they didn't truly understand the way that the cooling system operated.

If your builder was reputable, I'm certain that they knew about the steam holes on a 400 small block, and they used the right gaskets and drilled the necessary steam holes into the heads.

 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 16223
grumpyvette
Age: 66
Loc: FLORIDA USA
Reg: 03-16-01
08-24-11 04:50 AM - Post#2129584    
    In response to fcompoccio

  • fcompoccio Said:
I'm about to lose it. A couple of years ago I bought a 400 small block from an engine manufacturer in Washington state. Installed it in my 66 Impala with tri-power and a 350 Trans.

This car has been forever running very hot. I've done everything including recently installing an alumuminum large radiator with 2 electric fans. Everything is new and run antifreeze and coolant only no water and no thermostat. I think the steam hole theory maybe it. But what the hell are steam holes? I was a professional mechanic many years ago and worked on many small block chevys so I know a thing or two. But can someone tell me what to do and I'll have my friend who owns a shop pull the heads and do this steam hole thing. I don't know what else to do. Can someone take me through this in Baby steps?
Thanks in advance
Frank



read thru these threads

http://forum.grumpysperformance.com/viewtopic.php?...

http://forum.grumpysperformance.com/viewtopic.php?...
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


 
fcompoccio 
Forum Newbie
Posts: 37

Reg: 08-23-11
08-30-11 10:37 AM - Post#2131895    
    In response to clyde

I put a fully professional built 400 small block in my 66 Impala in 2003 and it has been running hot ever since spoiling many a cruise night. I did everything and spend a fortune every year to try to make this thing run cool. I have replaced everthing. This year I spent over $600 on an alumimnum radiator figuring this is it. Still ran hot! Read about the steam hole business just last week and am now in process of pulling the heads. The rebuilder swears that they always drill steam holes. Well we will find out what the deal is tomorrow. If the holes are there and the correct head gasket was used them I'm done. I only have 4,000 miles on this car since I built it, just can't go far. THERE IS NOTHING ELSE.

 
fcompoccio 
Forum Newbie
Posts: 37

Reg: 08-23-11
08-30-11 10:55 AM - Post#2131900    
    In response to Vaughn

I agree with eveything you say (in theory) however, when I put a thermostsat in and I've done it many thimes it just overheats sooner.

 
IgnitionMan 
Valued Contributor
Posts: 2713

Reg: 04-15-05
08-30-11 08:25 PM - Post#2132119    
    In response to fcompoccio

Please outline for us your cooling system, what you have for a radiator, old and new, water pump, fan, shroud, pulley size/ratio bottom to top, what ya' got?

 
fcompoccio 
Forum Newbie
Posts: 37

Reg: 08-23-11
08-31-11 02:22 AM - Post#2132152    
    In response to IgnitionMan

Please outline for us your cooling system, what you have for a radiator, old and new, water pump, fan, shroud, pulley size/ratio bottom to top, what ya' got?

The engine is stock bored 30 over. Built by S&S motors in Wash state. I have brand new tri-power built by Vintage Speed, headers and 350 trans the car was built for show.

I will outline for you the progress of the engine. The overheating was fom the day I first started the engine.

When I first installed the newly rebuilt 400 SBC I used the stock 2 row Rad, 180 thermostat, custom shroud, new pump and standard Chrome pulleys.

After the first year I bought a new 3 row Rad with aluminum pump.

Next year installed all metal hoses hoping to help dissapate the heat.

Next year I bought a the Radiator spacer for an a/c vehicle to get the Rad away from the fan and added fan spacers to a new thermostatic fan so the air would circulate better. (suppossedly)

Next year I put in a large steel flex fan and a large electric fan on the outside of the Rad with the stock shroud.

These changes went on and on to no avail. thermostat no thermostat, different fans etc.

After years of this overheating busines, this year I bought a large aluminim 3 row Rad with 3/4 inch tubes that has its own custom shroud and two electric fans built into the shroud. Guanteed to keep em cool. Checked references.

At the same time I installed a large pulley on the crank, new pump and P/S pump pulleys supposedly to circulate the coolant faster. Coolant circulates fine.

I have always used 50/50 coolant and antifreeze never pure water and never to be mixed with water per the manufacture. I have the Monte Carlo gauge package. the temp gauge stays in the middle if I'm on the highway doing 60 or better. Idling or slow traffic it climbs to HOT.

This year when I read about the steam hole business I said to myself this is it. I called the engine manufacturer and he claims he always drills the holes.

Now I have everything apart and very soon about to pull the heads.

I was a professional mechanic retired out of the business full-time since 1990 and have been writing auto repair manuals for the military and some work for Ford for over 30 years so I'm no novice just lost with this.

When the heads come off that one issue will be solved. Hopefully today. Then I'm really lost if the holes are there and the correct 400 head gaskets were used.

Anyone have any miracle answers cause I'm exahausted with this problem.

 
C10 Sleeper 
Valued Contributor
Posts: 3426
C10 Sleeper
Loc: Redding Ca
Reg: 03-17-09
08-31-11 03:56 AM - Post#2132170    
    In response to fcompoccio

I have had a few 400s that were bored .030-.060 over in circle track cars running in heat of 100+ degrees. My machinist said about the same thing everyone else has said. I never had any heating issues even while stopped under a red flag.
http://photobucket.com/C10Pictures


 
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