My 408 is running hot...please help!

[funbnme]

Having cooling issues with my 68 Camaro.

Here's the specs of my motor:
400 sbc .40 over...so a 408
400 crank & rods.
10/1 compression pistons...Keith Black ( I can add the part numbers tomorrow)
New street cam...not sure of specs, but it's not an aggressive race cam

Iron heads are good...no issues with them. I don't know the casting number, but was told they are 69 performance heads with good valves. Just had a valve job too. They are setup right for the 400 block. The builder does a lot of 400's, so he knows the motor and parts that work with it.

I know the 400's have the simese cylinders. My motor is setup to put out about 400hp to the wheels.
Now runs on 93 octane fuel.

current cooling system:
4 row radiator...not new, but clean. Doesn't look gummed up inside. Engine builder checked it out.
160 thermostat installed...brand new
15lb radiator cap
Electric Fan...but mounted to a shroud that's blocking airflow. It's basically an alum. plate that the fan mounts too, but there's no spacer between the alum & the radiator, so the only place the air flows through is where the fan is. Engine builder says it needs to go.

The shop that built the car uses this setup on all of the cars they build, but I don't think they've used a 400 block.

I have the Vintage Air setup. Coils mount in front of the radiator.

Tonights issue:
Just picked up the car from the engine builder. He was tuning up the motor before I took it home. Set timing, dist curve, carb jets...everything you need to do. The motor was completely rebuilt because the previous config required race fuel and was not streetable -- 12.8/1 compression pistons were in it.

Motor has 5 miles on it now.

Driving home tonight, the car got into the 220 range and keeps climbing after about 5 miles in traffic. That's from a cold start and without the a/c running.

I pulled over as soon as I could and let it cool down to about 140 on the gauge. That was about 40 mins on the side of the road.

I took off again and it got hot within a couple miles. Wound up pulling into a Shoneys ( of all places to have dinner ) and getting it trailered back to the shop that built the car...different than the motor guy.

Question:

For anyone here running a 400sbc with Vintage Air, what's your cooling system setup?

Can I run an alum. shroud that has space for airflow to go through the whole radiator and keep the electric fan? Will it flow enough air?

I didn't even have the a/c running...will this thing be able to keep cool with the a/c on? I live in South FL and it's hot down here...a/c is required for me.

I'd like to have part numbers and specifics on your setup so I can review everything with the shop & the engine builder before any changes are attempted.

Thank you for the help. If you have ideas or more questions...or want to talk me off the ledge...PM me your number & I'll call you during the day.

[70camaro406]

One question. Did your engine builder drill the heads for the steam holes? 400 small blocks have steam holes between the cylinders, and if non-400 heads are installed, they need to have steam holes drilled into the heads. Most, if not all, engine builders should know this about the 400, but I've heard of some that do not do it. That's the first thing that jumped out at me. Another is the shroud. It's always a good idea to get a shroud/fan combo that is made for the radiator. I have a Summit aluminum radiator that has a matching shroud and single 16" fan. No problems with cooling. Also, and this may sound crazy, is that you might want to actually increase your thermostat to 180-195. I've found that if the thermostat is too low, then you sometimes have a cooling problem. Worth a try. Good luck.

[funbnme]

I asked him about the heads & the steam holes when he was working on the motor and he said they are there. He's done about 4 other 400 block motors in the last year and I believe he knows the motor setup.

Do you have the summit part numbers for your radiator combo?

[Lowend]

10-1 with iron heads and a small cam and pump gas... I'm betting on detonation

[slowcamaro]

check timing... and lean = hot

[funbnme]

Update:
Stock shroud put on the car and the pulley mounted fan. Doesn't heat up as fast, but it still gets up to 212 just sitting at idle with a fan pushing air in front of the car and the engine fan spinning too.

Going to do a few things:
Change to an alumnimum radiator and increase the jet sizes in the carb from 73 Hi flow jets to 75. Carb is a holly double pumper. Going to see if this helps.

The engine builder says he got the tune close, but says to try jetting the car a bit richer (primaries) and see if that helps it out. There aren't enough miles on it to pull the plugs to check that out yet.

[Lowend]

212 at idle is not hot at all. L98 Vettes don't even activate the fans until 220deg
At higher speeds you get a ton more aiflow through the radiator than any fan can produce so the temps should be dropping at higher speeds.

[buns]

(1) Is your temperature gauge accurate? Was the rad boiling over?

(2) Food for thought. Mid sixties Corvette engines ran hot, so to quell the fears of new owners, they came up with a solution. They raised the red line on the temperature gauge to 250 degrees.


https://static1.pt-content.com/images/pt/2008/06/vettetempgauge1-1.jpg


(3) More food.


How Hot Is Hot?
Most people have been led to believe that 180-190 degrees is ideal, so they start to panic at about 200 degrees. Wrong. If we assume that your cooling system can maintain an operating temperature within about a 30 degree range under most driving conditions, then you should select a thermostat that will keep the operating range in the 190 to 200 degree range. Parts failure on a properly maintained engine should not be a consideration until water temperatures reach 250 degrees or higher.

Source:
General Motors Performance Parts
Crate Engines
Frequently Asked Questions




https://static1.pt-content.com/images/pt/2007/04/6-1.gif

[funbnme]

the guage I have starts to go into the red zone at about 215 or so. I know it's not that hot, but I don't know when it will stop.

We're going to put in the alum radiator and also a mech temp gauge so we can really see what the water temp is.

It wasn't cooling down at speed...it was getting hotter faster. That's why we think there's some type of problem.

Coolant never boiled...we shut it down before it got to that point.

[Kenova]

The first thing that grabbed my attention was how fast the engine heats up.
Take the thermostat out and test it in a pot of boiling water. Trust me, you would not be the first person to have a brand new thermostat that doesn't open.

Ken

[funbnme]

There's been 3 different thermostats put in the engine already with no change. Right now, there's a 160 thermostat in there. You can feel the hose getting warm right around when the gauge hits the 160 area.

[MonzaRacer]

First of all 212 isnt hot or boiling with pressure caps at 15 psi.
Never run just water it sucks for coolant regardless and will rust the block fast(I am a tech I see it several times).
Now as for cooling does it go higher or stay thier?
If it stays there when idling and goes down some at cruise your ok.
now if you really want to fix a hot 400 with overbore give Evans Cooling a call and order up a gallon or two of the flush, and enough NPG-R to fill the system.
If your have cooling issues with the Evans cooling products your never going to cool it.
Evans Cooling 1-888-990-2665.
This stuff works!

[funbnme]

At idle, it still keeps climbing. I have the original style console gauge. The line just before the red is 212...we checked that with a laser light temp gauge. I don't really know how hot it gets before it stops climbing...don't want to take a chance.

I know 212 isn't technically overheating...but it shouldn't run that hot if you're just sitting at idle with a water pump pulley mounted fan AND a fan in front of the car blowing air into the radiator.

More updates to come tomorrow.

[BlueBull]

I have a 400 +030. I was really worried about temperatures before assembly the motor because of all warnings I read. Anyhow, I use a summit high volume pump SUM-311017 with a thermal fan clutch and a fan shroud. Nothing special at all, and the best thing is the temperature is constant 170 degrees. If outside temperature is above 90 the water temp. dont rise more than a couple degrees. The difference to your configuration is that I use aluminum heads.

Not sure what your problem is, but I should defenitly try first another radiator and then another pump. The thermal transmission from water to air can suffer if the radiator is painted with inappropriate paint or to many layers. If block filler is used problems like this may also occur.

Good luck. /Emanuel

[Lowend]

It wasn't cooling down at speed...it was getting hotter faster. That's why we think there's some type of problem.

Coolant never boiled...we shut it down before it got to that point.

I'm going back to my original theory... you are having pre-ignition. Too much compression, iron heads and not much cam overlap.
Try backing off the timing or running some or 100+ octane fuel a see how it responds.

[funbnme]

The problem appears to be solved.

The radiator was changed to an alum radiator with more cooling capacity and it stays cool.

160 thermostat is still installed.

With the a/c off, it hovers in the 165-170 range.
with the a/c on, it's probably closer to 175.

On the side streets with stop & go, it gets to about 180 with the a/c on.

Car needs some tweaking still, but at least the motor issue appears to be resolved.

Thanks for all the support.

[paul67]

glad its sorted :cool:

[resto-mod]

I'm going to have to throw this out there. Maybe taking things apart accidently solved the problem. Didn't you say you had an electric fan? Did you say it got hotter the faster you drove? Was the fan maybe wired backwards(fighting the airflow)?

[funbnme]

The electric fan was removed and changed to a pulley mounted fan...it still ran hot.

I think it was a combination of 2 things.
1) The old radiator may have had some crust in it and it wasn't flowing water like it should have.
2) The alum. radiator helped bring the temp down not just because it was new, but also because it's alum.

It's running great now. Just need to spend some time trying to find the source of a vibration in the car....but that will be another post when I can't figure it out and need help.