Chevy 400 sb cooling headaches
 

After 3 yrs of running our 93 K3500 dually on 511 cid Caddy power, fuel prices dictated a change to cheaper running engine(over 8 mpg). We found a good running 1972 400 sb Chevy w/71K orginal miles from a wrecked kingswood estate sw.30 psi oil pressure after 40 min run time @ 180 degrees, no bubbles in the coolant. It leaked oil everywhere, so we tore it down to a short block, installed a new oil pump, an all steel oil pump driveshaft, new frost plugs, comp cams extreem energy 212@.050 cam&lifter/ timing chain set @ 0, Fel pro gasket set(for 400 w/steam holes), new valve seals, port matched the heads, offy dual port intake, msd street fire distrid w/accell cap,33 degrees btdc @ 3500 rpm. 1.52 semi roller rockers, Wieand aluminum water pump and moroso reverse opening 160 thermostat. OE diesel oil cooler,radiator and 3/8" fuel lines and Holley red fuel pump and 650 holley spreadbore carb. 2-16" electric fans and 22psi rad cap. All the cooling parts cooled the big Cad with 10K lbs on trailer on 90 degree days.
Now that it's 65-75 degrees here the 400 runs HOT, at 230-240 when towing and has hit 245(where the safety system shuts it down) and is never less than 210 when towing after 5 min. I have a 160 amp old school caddy limo alternator and dual batteries or the fans would overwhelm the oe alternator.
The 10w30 oil got so thin after a week that I can hear the rods when warmed up with the stethiscope.
At this point I'm ready to make whats left into a vortec 383 unless anyone has a good idea on what could cause this.

Re: Chevy 400 sb cooling headaches
 

Do you think that the t-stat is staying open and not letting the water in the radiator cool enough? 160* is kinda cold for a SBC. When you pulled the heads, did you clean out the steam holes?

Re: Chevy 400 sb cooling headaches
 

Did the heads even have steam holes? Almost 40 years is a lot of time for someone to have put on different heads. A motor that runs warm always keeps a little sweat on the ole brow!

Re: Chevy 400 sb cooling headaches
 

Could be running lean/rich running hot.
Posted via Mobile Device

Re: Chevy 400 sb cooling headaches
 

An old school small block in a 1 ton dually pulling 10K plus on a trailer. Really? Those things would overheat in a 2 door Impala going down hill.

Re: Chevy 400 sb cooling headaches
 

Did you hear and drive this good running 400, or were you just told it was good running?

Re: Chevy 400 sb cooling headaches
 

The T-stat is opening, you can see the coolant circulating in the fill neck and the electric fan sensor is in the radiator by the top hose and the fans come on and off at warm idle. The steam holes in the block are open, we ran the rifle brushes through all the deck holes while apart. We have many things to drive, the dually sits if it's not pulling a load so 160 is ok, It never stays at that temp.
The steam holes are in the heads,they are 400 2bbl heads and they were hot tanked at the machine shop, in addition my guy does bronze guides, 3 angle valves, pc seals and pinned studs, checks springs for $275 a pair, not bad price.
Throttle response is very good, no stumble, hesitation or anything. And the spark plugs are nice and tan, not black or glazed the fuel mix seems ok and I had to change them today as they were AC rapid fire and the plug wire boots were too close to the headers. Accell shorty plugs now. the fuel mix seems very close to perfect.
You can do many things with a 8.75 to 1 compression 400 with cam, head work, intake manifolds, headers, ign timing and such. This is an ex cab 4x4 dually and when empty it walks all over my '98 K3500 CC lwb single wheel truck with the 5.7 vortec to the tune of 78 mph on the on ramp that the '98 can only get to 66 mph on. They are both geared 4.11
The car had sitting back by the trees in the wrecking yard since 1983 or so. It was hit so hard in the back that the driveshaft was bent. We looked at it, checked to be sure it was a 400, they took the loader and carried it to the yard's shop, ran a file acrost the points, check the oil and coolant, put an oil psi gauge in, hooked up a boat fuel tank to the fuel pump, hooked up the battery cart, put a squint a fuel in the carb and amazingly it started and ran. It smoked blue for a minute(they oil the motors down routinly) then cleared up and we let it run for 45 minutes, revving it up and down, had the stethiscope along and the infared temp tool along, it never went over 180 degrees, never dropped below 30 psi on the oil gauge, didn't shake the dime on the air cleaner the only thing we noticed was oil leaks everywhere. 50 degree day. Gave them $350 for it and waited while they torched and cut it out.
So today we 1- moved the oil cooler over 8" to the right so it is directly in front of the left fan, 2- changed the coolant from 50/ 50 to a 70% water/30%, 3- added a "water wetter" additive and, 4- changed the oil to 15w-40 to help resist the heatplus 5- took 2 degrees out of the timing as when you get to 235 the msd knock sensor would start lighting up. I'm wondering if the high flow water pump is moving the coolant a bit too fast, and does not have time to absorb enough heat. Monday I will know if this helps much/alot, or if any.Thats all there was time for because of the 4L80E problems that are in another post.
You know, I expected all this 3 yrs back when we put the Caddy in, just about everyone told me the Caddy would overheat in a truck, and while the big Cad never went below 190 it never went higher than 215. It did like fuel though, but I guess thats the trade off for the ability to do 5 or 6 wheel burnouts. Thanks to all of you for all the help !

Re: Chevy 400 sb cooling headaches
 

I've never had a problem with a 400 if everything is good.I run a 400 with a comp cams EX250-H cam speed Pro 9.5:1 pistons. I do have 76cc heads that I drilled myself and I run a 4 row Desert Cooler and a 160 thermostat and a Summit Hi flow water pump. I towed a 6500 lb trailer out west last June and July and even in the Mts I had no trouble staying below 210 deg. I have a 5 spd NV3500 and 4:10 rear gear. Towing should be no problem.

Re: Chevy 400 sb cooling headaches
 

I have a 400 in my '73 daily driver. The truck originally came with a 454 and is still has the big block radiator. It hardly ever gets past 180, sometimes up to 200 on a warm day in traffic.

I would guess there's still a bubble in the system. A 22psi cap seems a little high to me. I would try a 16psi cap and see if it changes anything.

Re: Chevy 400 sb cooling headaches
 

Is it possible that you have the wrong rotation water pump for whatever type of accessory drive you are running? Are you running a serpentine accessory drive?

Re: Chevy 400 sb cooling headaches
 

The water pump is the correct rotation for the 1972 engine and we run it with the 1972 brakets etc.
Update- Yesterday we ran it, it was about 40 degrees here, and around town it never went past 210. but on the way back we took the hwy and hit 240. I talked to my machinest(do his lawn/snow also) and he said with the heads he had to hot tank them twice as there was alot of whit/yellow scale that did not all come out on the first time through. If that stuff was in the heads cooling passages, It must be in the block also and that would act like a barrier to block the heat from the coolant. when we got back we let it run and used the infared temp finder and hear's what we found.
Rear right of block-295
Left rear of block-305
oil pan-226
left head rear 292
right rear of head-301
front left head- 291
right front head-300.5
water neck-240
water pump inlet-165

All this explains alot to me about this problem, And with the main bearings starting to make noise I dug out the old 350 4 bolt that we saved and with the help of the machinest were making a long rod vortec head 385(.060 bore) and leave the 400 block in the corner for another day. Thanks for all the help, I appreate it!

Re: Chevy 400 sb cooling headaches
 

Ditch the high flow water pump. A stock water pump moves more than enough water.

Gary

Re: Chevy 400 sb cooling headaches
 

I have never had good luck with 400's. I had a 72' that had one in it that was swapped in sometime in its past that would run at 220 even in 65 degree weather. Another was in a 79 k20 that was stock and a total gas hog. I mean if i'm going to get 8MPG then give me a big block and let me have the increased torque to go with it. All of them i have had i either junked or traded for 350's. There is a reason they had a relatively short service life in GM vehicles. I think 10 years or so. A old GM mechanic who worked at Diller Chevrolet told me once that the 400 SBC was the only small block he would never recommend. Way to many would come back with issues due to cooling.

Re: Chevy 400 sb cooling headaches
 

The one and only 400 I had experience with was in my uncle's 71 Chevy kingswood estate wagon. He bought it new, and in 1974 he needed my Dad's spare car as his was in the shop for motor overhaul ( it had 42,000 miles on it). In 1977 he gave it to us and of course as I had just got my DL so thats what I got to drive. It took me a yr to get my own car, but it held up well so long as you didn't hammer it or run high (over 80mph) speeds. The local Chevy dealer told me that the car did not have enough air flow/radiator for performance usage. Thats what I had in mind when I found one for our dually, needs more airflow/radiator, better on fuel than the built Caddy, sb chevy so low cost parts. I have a 1972 402 laying around and I wish that I had not given it to my son for the 87 Camaro project.

Re: Chevy 400 sb cooling headaches
 

Honestly, I think a gas motor for this situation is the wrong direction. I have a feeling the new motor you are having built will probably get 8 MPG or less when heavily loaded.

A Cummins 6BT swap would give much better power and gas mileage. Yes diesel costs a little more, but they maintain better gas mileage when loaded and they are an industrial grade engine, which means that motor is going to have a very long useful life.

Re: Chevy 400 sb cooling headaches
 

In the stop and go yard care world, diesel lawnmower yes. Now the truck you start, drive 3 mi, park for 35 minutes, restart go 5 city blocks, park for 50 min, restart, go 2 blocks, stop and mow lawn 40min, repeat repeat repeat 10 hrs day, 5 days a week. The 93 dually was a diesel, it only took 3 6.5 TD to go 115K mi. I also have an 82 2500 that was a 6.2, It had a crate motor(6.2) that had just been installed-that made 37K miles. So you say GM diesel is junk? We killed a 1996 F450 powerstoke 7.3 in 71K mi, and that was only part time for mowing, and Dodge? My local dealer sold us his personal 3500 lariet 4x4 with only 51K mi in 2005 and when we lost the truck in a lawsuit in spring 2008 it had a new crate cummings in it. NO more diesel trucks for us. They do have better power, are a bit better in milage, get stolen if you leave them run unattended and cost between $5500 to $7942 to replace engines in. We leased a Duramax in 2008 and let it go in late 2009 as it was injectors, injector wiring harness, egr failure, ecm needed reflash, TCC malfunction all in 2 yrs, fixed under warranty for sure but I don't like paying 4 weeks a month for a truck we only get to use 3 weeks a month 'cause it's at Koceuric Chevy again.