Tbuck2007

So basically, I have an 1989 Pontiac Trans Am. Me and a buddy ripped the old TBI 305 out of it, put a small block 400 into it. It was a pain in the butt, but we got it running finally. About a couple weeks in, I finally got my exhaust done. The morning after I got it done, I went out and let the car run for 5 minutes to warm up, came outside to see smoke coming from the hood. I figured it was just the paint coming off my headers..sure enough when I popped my hood I saw steam coming from everywhere..the resevoir tank was spewing/shooting steam, and coolant out, so I immidiately shut the car off. Three seconds later a really loud explosion happened, sending coolant everywhere. I ended up blowing a top radiator hose into three pieces, which was brand new.
I check themostat, was fine, replaced, etc etc..For some reason the coolant is just, acting weird. I got this motor rebuilt off a guy around here, came out of a 72 impala supposedly. It was fresh rebuilt to stock.
its a smallblock 4 bolt main 400. ANyway.
I changed the hose, put coolant in, changed thermostat, but still the car runs just fine, runs perfectly fine. Drives fine. (By the way I dont have gauges in the car quite yet..working on it), but when you let it run, then shut the car off, if you take the radiator cap off, it spews out coolant from the radiator.
A guy that looked at the car told me the water pump was turning backwards, causing pressure buildup, less coolant more air into the motor, because the water pumpw as turning Counter clockwise. Well the belt diagram shows this, and we are almost positive this water pumpwe took off came off of the 305 that came with the car. THe belt diagram shows the pump running in reverse..

Any thoughts that could be wrong with the motor? Blown head gasket..?

Thanks.

TB07

Air_Adam

Which water pump are you using with what belt setup? The V-belt setup has a water pump that turns one way, serpentine setup has waterpump turning the other way. You can't mix and match here.

Also, once the cooling system is hot, its normal to have coolant spew out if you pop off the radiator cap. Theres pressure in there, and there is supposed to be.. pressure raises the boiling point of the coolant.

What thermostat do you have in there?

Tbuck2007

Its all serpintine belt set up, and Im not sure what thermostat..I believe its the one for the car, so the 305 E motor. And its normal for coolant to spew out of a radiator cap you say? when the caps off..?

five7kid

iTrader: (14)

It's normal for it to spew out when hot and first opened. There's about 15 psi of pressure on the system when hot.

However, if it keeps spewing out, then the coolant is boiling in the engine. You really need to get a temp gage installed so you know where you're at.

What kind of radiator fan do you have, electric or engine-driven? I'll assume electric, since it's an '89 and you have a serpentine belt. Does the electric fan(s) come on when the engine gets hot? You didn't mention that anywhere. I had a cooling fan failure that produced the spewing results you described.

A new upper hose blowing into pieces sounds weird. Have that radiator cap pressure checked, or just put on a new one.

The pump should rotate in the opposite direction than the crank. If you put on the 305 pump, it should be fine. If you used the 400 pump, it's rotating backwards and would probably cause problems. I'm afraid the "guy" who looked at your car doesn't know what he's talking about, though.

What heads are on the engine? If not 400 heads, they have to have the steam holes drilled using the head gasket as a template. Or, the "builder" could have used generic SBC head gaskets that don't have the steam holes. It's more of a hot-spot issue than an overheating issue, but something to verify.

If those are factory 400 heads, and you overheated it like it sounds from your description, then you very well may have cracked heads now.

Tbuck2007

well, The fan is electric, I have it on a switch and yes it works..and yes its a bone stock motor, a 400 SB..so I guess I just need to rip apart the block.

five7kid

iTrader: (14)

Not necessarily. I said "may have" cracked heads. But that's a result, not a cause of the overheating.

I'd be sure about the pump type before doing anything else.