Is my 400 sbc gonna hold up in my 85 trans Am during the summer or am I gonna end up cracking the heads or something.
Should I upgrade the coolant system? if so what should I get.

i too am worried about that with my 408. the guy who did all the machining for my block (also a good friend of mine) said that alot of it has to do with the way the block is hot tanked. because my block is from 1971 it is very old and has alot of crap in the water ports. he said i should be fine because he cleaned it out real nice for me. hope this helps.

I think that you should be alright IF you had the steam holes drilled into the heads. Some people have been able to run it with all stock components. Others have upgraded there water pump to a Steward Stage 2 and a Griffin radiator or similar. The 400 got a bad REP for overheating because people was switching the heads off the 400 and did not drill the steam holes, causing the block to overheat. If your heads have the holes drilled you should be OK
Hope this help

only reason a 400 over heats any more than any other SBC is because someone runs heads without drilling the steam holes and not knowing any better blames the 400 for their mistakes.

If the engine's built right, it won't overheat, crack heads or anything like that.

However, you MUST have an adequate cooling system or risk overheating just due to the systems inability to reject enough heat. When switching from a 350 with iron heads to, say, a 400 with aluminum heads it is inevitable that more strain will be put on the cooling system. The factory radiator will handle it OK, if it's in tip-top condition- if not, might as well replace it now. I highly recommend using a high volume water pump and not a parts store rebuild (although they will work, they're not ideal). Also, make sure your cooling fans are up to snuff and that the "chin spoiler" under your radiator support is present and in good condition. Adding a 3rd "pusher" fan in front of the radiator to supplement your twin stock fans is a good idea. It should be wired to run either all the time or turn on at the same time as the first fan.

This comes from my recent experience with a 400-powered 87 GTA with aluminum heads. It pushes the limits of the stock cooling system on hot days, but these upgrades have made enough of a difference that it no longer gets anywhere near the "danger zone."

been runnin a 406 since 1988-build it right and its gonna be fine.(thats the same 406) not several. been together since. and thats livin thru my silly nitrous years, reckon though that this blower kick im on now may injure it, but you never know. :lala: well there are those pesky siamesed bores if we are gettin technical

I've been a fan of the 400 for a long time. Several people already posted the reasons that 400's got a bad rep for cooling problems...NOT drilling the steam holes in the heads.


As for the stock 3rd gen cooling system being able to handle a 400, depends on the shape of your cooling system


The last 400 I worked on was for a friend of a friend. We put it in a G Body.

Using a stock replacement 3rd gen alum radiator, 160 thermostat, hi flow water pump, and a single electric fan, the car kept cool. 180 or less on the highway, and even with the AC on and idling in 90 degree weather it never got past 210 or so on the Autometer gauge.


I see alot of people say NOT to use a 160 thermostat...I say why not? It's not like using a 160 thermostat is going to make your engine run at 160 degrees if you're using a stock-type cooling system. The system is designed to run at or near a certain temp ( 200 degrees F or so for the 3rd gen ) and just changing the thermostat to a lower temp won't have a dramatic effect.

Another thing to keep in mind is to GET RID of the factory temp gauge for a quality aftermarket gauge. I'm a fan of mechanical gauges... but that's just me. And I like knowing the temp even when the key is off.

I once had this bad overheating problem with another GM car. Gauge was hot all the time....replaced all this crap, same thing. Put a mechanical temp gauge on it, and it wasn't running hot at all.


Hope this Helps.

you know i need to say that a lot of what makes us better wrench turners is the ability to FIX things. why is it someone has a problem with part "X" or subsystem "Y" suddenly its the big bad cars fault and it cant be fixed because its just a "NO GOOD...(fill in the blank). this is how mechanics originally came into being. they fixed things. if one were to listen to some of the silly nonsense put forth here they would have over half the car thrown away because its bad, nogood, yadayadayada. im not saying that there arent problem children cars or some cars arent a little(a lot) pre-disposed to certain problems, but jeesh, this kind of zaniness isnt really helping out at all,where is the big bennie to not keeping the o.e. gauge (btw-gm makes somepretty accurate gauges) because the homework wasnt done and proper diagnostics werent performed? why are you trusting the autometer? just because its telling you what you want to hear? whats to say the autometer is correct and the oe isnt? i dunno its just pissin me off seeing this kind of "help". heres yet another classic, i cant help it its gotta be done-- um im speechless now and im gonna hurl. if this is what good info is, i apologize for not recognizing what i was reading and please carry on. and not another peep out of me..

You posted......

The big "bennie" to not keeping the OE gauge is the fact it's not that accurate to begin with. I've personally worked on a good bit of GM products over the years. Alot of these were 80's- early 90's. And MY experience with the factory gauges in MOST of these vehicles has been consistent. The water temp and oil pressure gauges have almost always never been that accurate....and the tachometers as well. POST A POLL on this board to see how many 3rd gen owners have tach's that read incorrectly.....

How did I judge them this way? By testing against a mechanical gauge, or alot of times by the data output from the sensor.

Maybe I structured my post in a way that's not clear. I prefer mechanical gauges for pressure readings. I happen to have had a good experience with Autometer. A gauge with a DIRECT FEED of the fluid being measured for temp or pressure is normally going to work or not...not read innacurately.

Have you ever examined the IP connection for the gauge cluster in a 80's GM car? Over time the connections become flaky. Can it be fixed? Sure. Can the OE gauge can be replaced? Yes. But why not replace it with a newer, better designed part?

I wasn't blaming any part of the car.

Is the stock 5 speed shifter adequate? Sure. For 90 percent of drivers. But the other 10 percent know it can be improved upon. That's how the aftermarket performance auto industry was born. People improved upon problem areas and existing parts to make that system perform better.


As for your response to my post regarding using a 160 thermostat......


What is this? You having a bad day? Sorry...but I didn't do it.

MY point regarding the 160 thermostat is simply that the GM cooling system in a 3rd gen is designed to run at @200 degrees F or so....with a 305 or 350 engine. Not an additional 50 cubic inches. And as you pointed out earlier, the 400 tends to run warmer for 2 simple reasons. It has 50 more heat producing cubic inches and there is not cooling passages cast into the block ( like every other SBC ) because there is simply no room. The cylinders are that close together...thus siamesed.

Every case I've personally seen involving a 400 swap, usually involved the engine running warmer than the previous smaller cube engine.

And the 3rd gens tend to run warm at low speeds anyway ( high speeds if the air dam is missing......got a nice Firebird for $300 this way once...owner thought blown head gasket. I replaced the air dam and turned the car to a buddy of mine for a $1000 and he was thrilled......it was actually a nice car. )



And I wonder...with all the time / money you have invested in the engine in your signature, you still using the stock gauges? If so, more power to you. Guess you have more faith in mass-produced 80's automobiles than I do.


Chris
Who can't believe I wasted 5 minutes of my time posting a response to you.

peep