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So for my first post on here+ first day owning a 3rd gen and I'd appreciate some advice from those more knowledgeable. My car overheats like hell, (400 small block with a cam and goodies, 4 core aluminum rad with dual e fan) so I'd assume it should be okay. But nah it's touching 260 within 3 miles of driving and it doesn't cool down on the freeway either. Other basics about the car, it's allegedly got 20 odd miles on a freshly build motor with break in oil still in it. That's been sitting like that since 2003, knowing this my best guess is throw a thermostat, then water pump at it in that order and go from there. But I'd like to hear yall advice on this deal. Also what water pump am I gonna need as this things a random 400 sbc (330817 is casting# I believe) Fiberglass cowl hood to fit the air cleaner \"Super Turbo" Muffler at the back, and a new gas tank! The 400 (I think, was told it was a 383 stroker) What water pump is this, he converted it to serpentine belt drive
I agree w the air dam point. It looks like you have an electric fan. Does it turn on? If so when? Do you have a full shroud around the radiator to force air through it? Yeah, I put a new thermostat in as a starter. If I remember correctly 400s are less of a fan of being over heated. My stock fan/radiator cooled a 430hp 350 pretty well.
also, make sure it's a reverse rotation water pump. That's what serpentine stock conversions
require.
Last edited by Firechicken82; Aug 31, 2025 at 09:39 AM.
It's not the air dam; that won't cause "260 in 3 miles of driving"....or any overheating when sitting/idling. Overheating while not moving is typically fan(s) not working. Over heating while going down the road could be a lack of air dam....but that's not the root problem if he's overheating under all conditions or while not moving.
I SEE one problems, in those pics; No cooling loop w/the thermostat closed. You need to have coolant circulating when the stat is closed. That rubber capped nipple on the intake SHOULD run to the heater core, back to the water pump and there is your loop when the stat is closed. Someone capped it, so you need to fix that.
* First, confirm proper water pump for reverse rotation belt drive. If you got a CW pump spinning CCW, it ain't gonna pump watah...and it's gonna over heat. Bub.
* Second, When it's getting hot (above t-stat opening temp)....what's going on in the radiator? Is it cold? HOT? What's the radiator got going on when the engine is hot?
* Third, fix that coolant loop that bubba f'ed up.
just another idea on that too, u sure you dont have air in ur system? i vacuum sealed mine twice and still had an issue until it burped itself out after. only after a 30min drive itd boil and bubble out. i'd squeeze the rad hose to thermostat to check if ur getting coolant/ an air pocket
Lack of coolant would definitely cause the symptom described, but it would have to be a lot more than a little air in the upper rad hose. It'd have to be something like 1/2 gallon low (1/2 gallon of air) to create that much of a performance deficit. And when driving at highway speed (RPM), the pump would likely overcome gravity anyway, and loop the coolant and cool "good enough". Plus, I was giving the OP credit that he did check to make sure the system was full.
It's not the air dam; that won't cause "260 in 3 miles of driving"....or any overheating when sitting/idling. Overheating while not moving is typically fan(s) not working. Over heating while going down the road could be a lack of air dam....but that's not the root problem if he's overheating under all conditions or while not moving.
I SEE one problems, in those pics; No cooling loop w/the thermostat closed. You need to have coolant circulating when the stat is closed. That rubber capped nipple on the intake SHOULD run to the heater core, back to the water pump and there is your loop when the stat is closed. Someone capped it, so you need to fix that.
* First, confirm proper water pump for reverse rotation belt drive. If you got a CW pump spinning CCW, it ain't gonna pump watah...and it's gonna over heat. Bub.
* Second, When it's getting hot (above t-stat opening temp)....what's going on in the radiator? Is it cold? HOT? What's the radiator got going on when the engine is hot?
* Third, fix that coolant loop that bubba f'ed up.
Thank you all for the solid advice, I'll attach a photo of the kit that was swapped, I'm assuming since all the accessories came together the water pump should be ccw as that's how the belt is routed. Got a new 180F thermostat and some water wetter. The heater core is disconnected and the reason it was plugged is the fuel like routing, the input for the carb blocks where the heater hose would go so I'm either going to have to bend the hard line or get a 45 degree one or something. The air dam is there, but is for a mechanical fan car so not sure how effective that is. Lastly, the fans do kick on at around 200/220 I need to double check the relay forsure but the temp sensor on the intake is how it's hooked up, the cylinder head temp sensor is for the dash gauge. And they do have a small metal shroud containing them to the radiator, which was getting hot when the car was overheating. Going to put thermostat in and some water wetter, will update in a few Belt routing More routing This is the conversion kit that is on the car currently
If you have the wrong pump, just get a stock replacement. Don't waste money on a "high flow" pump or anything like that.
My O'Reilly pump cools my 383 just fine.
My money is on a coolant flow problem not an airflow problem based on what's being described.
The rad is full, so is overflow. I don't think it's air in the system. I swapped the thermostat and it still overheats after 3-5 mins of driving. Going to get a new water pump and go from there.
Yep. Both you guys have CCW rotating belt drives. What is "wrong" with the OP's routing is that there is not enough wrap on the PS pump...thing will slip like a **** when turning at low speeds.
EASY BUTTON TIP for accessory rotation: If the BACK/smooth side of the belt wraps a pulley; that pulley will spin CCW. If the GROOVES of the belt wrap the pulley, the pulley will spin CW.
In addition to poor belt routing, you appear to have the wrong water pump.
AFAIK there are NO CCW rotating WPs that support the fitting on top for a heater hose nipple. That feature identifies your WP as CW rotating.
Get the right WP. Needs to be 88-up; AFAIK doesn't matter what chassis you ask for, butt to assure compatibility, order whatever your accessory drive setup came off of. Might make a MASSIVE difference to have one that actually pumps.
And of course, get THE RIGHT belt at the same time, and route it RIGHT, so that your accessories all get driven properly. To do that you'll need the "smog delete" pulley w bracket, which you can get from GM.
In addition to poor belt routing, you appear to have the wrong water pump.
AFAIK there are NO CCW rotating WPs that support the fitting on top for a heater hose nipple. That feature identifies your WP as CW rotating.
Get the right WP. Needs to be 88-up; AFAIK doesn't matter what chassis you ask for, butt to assure compatibility, order whatever your accessory drive setup came off of. Might make a MASSIVE difference to have one that actually pumps.
And of course, get THE RIGHT belt at the same time, and route it RIGHT, so that your accessories all get driven properly. To do that you'll need the "smog delete" pulley w bracket, which you can get from GM.
edit; also looking into smog pump and possibly ac compressor delete altogether. Neither will be hooked up for this build and I already don't have the condenser in there. If anyone can point me in the right direction as to if I can keep the brackets that mounts my tensioner and just remove the ac and smog pumps and just get a shorter belt, or if I'll need to get a new tensioner bracket. Thanks all for the warm response on the forum as well, glad to see this part of the car scene is still alive and well.
I bought a 90 Camaro water pump and that helped w heat at idle but still overheats after about 7-10 mins, it still has the port on the top but definitely pumps better. I had an incorrect pump originally. Bought a 16" pusher fan 2600cfm and I'm going to get a 90 degree fitting for the coolant plug on the intake and route it to water pump akin to this setup I saw today. Hopefully these both will fix the issue. Drove it a little today and it was still getting way too hot. I intend to set mine up like this, instead of having it go from water pump to thermostat however I will route mine to the intake port that's plugged in the left side. This is mine currently with the 1990 Camaro water pump (CCW) I will get a 90 degree fitting for intake and route it to water pump. And add the pusher fan. If this doesn't work I'll bite the bullet and route the heater core properly but I really doubt what's what's causing this overheating issue. Also I need to flush the block and rad because I put new coolant but it turned dark immediately
Last edited by Sh1tboxEnjoyer; Sep 2, 2025 at 06:48 PM.
Reason: Adding more information and spacing
A cruded up cooling system could have a lot to do with it getting hot.
100%, flushed the rad, block, installed 2600cfm fan with proper shrouding, and was able to idle and rev a few times in the driveway for 15 mins before it started to touch 220. the Motor has break in oil and less than 50 miles. going to do an oil change with 10-40 and zddp. Plus it has fat jets in it and is running far too rich right now, and i think it has too much timing because its popping and banging on cold start. Hopefully the slight tuning will finally be what gets this thing under control, and ill report back here once ive done that. But again, anyones two cents are always appreciated!
phone edit, here's pics of what's going on above Water pump to intake loop Upper rad hose was connected by a plastic one of these that promptly started leaking on first start up, slapped this in and no more leaks Not pictured is the custom brackets I had to make to mount the fan to top and bottom of rad, opposed to going thru it with the provided mounts as they would contact the fans on the other side.
Last edited by Sh1tboxEnjoyer; Sep 9, 2025 at 02:09 PM.
You mentioned putting in a new TStat. Hoping it wasn’t a cheapo from an auto parts store around the corner.
i had a new one and in just a few months, I noticed it would never get up to temp ( opposite problem). In my case the plunger/spring assembly got hung up in the open position.
i wouldn’t overlook a bad non opening new stat.
assuming you’ve done a cold start test and are able to witness a cold soft upper radiator hose at first and once to temp (190 ish) it opens and you feel a warm rush?
* Second, When it's getting hot (above t-stat opening temp)....what's going on in the radiator? Is it cold? HOT? What's the radiator got going on when the engine is hot?
