SBC 350 Overheats

4454 Views 86 Replies 12 Participants Last post by Joe White, 7 mo ago

Joe White

Discussion Starter · 11 mo ago

I've been battling an overheating issue for quite some time. Now I do understand it is 100+ degrees out right now, but I'd like to believe the engine should still be able to cool itself off.

I've got a big three core aluminum radiator, with dual electric puller fans, and smaller electric pusher fan. Running a 195 thermostat at the moment, was running a 180 (no change). There is ac in the truck, but the overheating problem still exists with the ac off. I am able to open the hood and let it idle and it will cool down to around 210. Doesn't seem to matter if I idle or drive around, if anything heats up faster when driving around.

The trucks radiator appears to keep up for the first 3 or so openings of the thermostat, keeping close to 195. But after than it seems to overpower the radiator, and the fans are just blasting 200 degree heat constantly.

Here are some picture for reference.

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Joe White

Discussion Starter · #21 · 11 mo ago

Rhotpursuit said:
Get the Intrepid fans...6 blade.

I’ll need to check on the width. The fans that are in it are almost touching the water pump. With the ac condenser and enormous radiator it’s a tight fit. But if they will fit I’ll get some of those fans.

bk2life said:
have you tried a second temp gauge? just to make sure youre not chasing the dragon?

I actually already have 2 temp gauges. One for the normal style gauge and one that goes to the Holley Sniper. I know the normal style gauge doesn’t work correctly. It’ll show around 240 when I’m at 200. But the digital one for the Holley works. I also have a temp gun so I’ve checked it with that.

All in all I do believe it to be the fans not pulling enough heat out in time. Slowly creating the overheating.

Rhotpursuit

· #22 · 11 mo ago

You can always recess the radiator into the core support. The downside is your radiator is so thick that you'd have to put the condenser on the other side of the core support. That raises the issue of modifying the hood latch support.

You could get a stock 4.3 radiator and condenser recessed in the core and have plenty of room.
I know yours is a 1st gen, but this is what we did to mine. 2000 Grand Am radiator and condenser that snaps onto the radiator...

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Joe White

Discussion Starter · #23 · 11 mo ago

Rhotpursuit said:
You can always recess the radiator into the core support. The downside is your radiator is so thick that you'd have to put the condenser on the other side of the core support. That raises the issue of modifying the hood latch support.

You could get a stock 4.3 radiator and condenser recessed in the core and have plenty of room.
I know yours is a 1st gen, but this is what we did to mine. 2000 Grand Am radiator and condenser that snaps onto the radiator...

Looking at the distance I have between the radiator and engine, I cant get any fans bigger than the ones that are in it. Which are only 2.5in thick.

oldeerslayer said:
I'd try putting a kill switch on the fans that you can flip in the cab. I'm willing to bet he'll see his temps go down by shutting them off above 50 mph. Just don't forget to turn them on when you slow back down.
I also think his fans look too shallow to seriously move enough air. CFM ratings from the manufacturer need to be taken with a grain of salt. 225 watts at operating 13.8 volts is 16 amps. At Battery voltage of 12 volts it's 18.75A.

So I gave that test a go, drove around 55-60mph turned off the fans while driving, temperature quickly rose from around 201-202 to 216, within a minute.

Turns out my AC compressor leaks, so I couldn't test it with the ac on as it stopped working. But today being right at 100F outside the truck would hover right around 201 when driving around, with the fans constantly on.

Rhotpursuit

· #24 · 11 mo ago

Joe White said:
Looking at the distance I have between the radiator and engine, I cant get any fans bigger than the ones that are in it. Which are only 2.5in thick.

So I gave that test a go, drove around 55-60mph turned off the fans while driving, temperature quickly rose from around 201-202 to 216, within a minute.

Turns out my AC compressor leaks, so I couldn't test it with the ac on as it stopped working. But today being right at 100F outside the truck would hover right around 201 when driving around, with the fans constantly on.

You might have to bite the bullet and get a thinner radiator.

Joe White

Discussion Starter · #25 · 11 mo ago

Sorta not a update, but an update. Nothings changed, but I want to know if it is possible to do a mechanical fan, or it is just better to upgrade to better electric fans. I've had the worst time with this truck the past few weeks, needed a new ac compressor, alternator still wont charge after a new one, struggles to idle and start, and of course the overheating problem. But I never really understood how little air the electric fans moved. Seemed like plenty to me at first, but then I went over to my big suburban and with its mechanical fan it was blowing 4x as much air at idle. So in the end I'm putting more money into the truck no matter what, but not sure what option is the best, especially considering I plan to use the ac. Also radiator options, I will try to get back the smaller radiator I had before the one in it now.

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Rhotpursuit

· #26 · 11 mo ago

Somewhere on JTR is an article about using the 4.3 radiator (I Think). They used a clutch fan from a Ford. Seems they are about an inch thinner than the stock piece. They should fit in the 4.3 shroud without a problem.

Joe White

Discussion Starter · #27 · 10 mo ago

I went to a pick n pull, grabbed fans to which I believed to be similar looking to what was suggested. Turns out it wasn't exactly, and the fans I got only does 800cfm. I a little confused on all the cfm numbers, since there is two would that mean for each, or both. Because the fans I have now show 2600 cfm. Also clarifying the fans I have I have confirmed to be MJS26K Jetstreme series. I'm pretty tired of spending money. If there is something I can find easily online that should be able to cool I'd be very interested.

Joe White

Discussion Starter · #28 · 10 mo ago

Rhotpursuit said:
Get the Intrepid fans...6 blade.

After returning to the junkyard and returning the fans I got, turns out the only intrepid they had the fans were off it.

so…I bought the Four Seasons brand version of the intrepid fans. Saw someone else post the same one I got on the forum.

ive looked into a couple of things more. My problem with overheating I believe consists of 3 things. One being the recirculating of hot air, two the fans not pulling enough, three the fans probably are not getting as much power as they should. The wiring used for those fans appears to be something like 16 gauge. Which did get warm under load. I’m glad I caught onto that.

Upgrades obviously being the new intrepid fans and wiring. I planned to use 12 gauge wires. But that might not be enough for the intrepid fans. Also what amp relays should I use.

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Gen210

· #29 · 10 mo ago

Many of the aftermarket "Intrepid" fans are NOT dual speed as the factory models that is why there was a ridiculously low price on them last year Or so.

Joe White

Discussion Starter · #30 · 10 mo ago

Gen210 said:
Many of the aftermarket "Intrepid" fans are NOT dual speed as the factory models that is why there was a ridiculously low price on them last year Or so.

I’m not sure if this ones not two speeds. A bunch of the reviews people seemed to like it. I don’t care if it has two speeds though, I could always just turn one fan on later then the other one.

Rhotpursuit

· #31 · 10 mo ago

@oldeerslayer discovered the fans were wired incorrectly. I think he rewired them to work like they should.

Joe White

Discussion Starter · #32 · 10 mo ago

Another update. Got some new fans installed from Summit, Last fans were around 2600 cfm these show 3,700-3,799 cfm. so a noticeable difference. Now I noticed that while it helped some it didn't seem to fix the problem. 100 degree days seems to drive fine without the ac fine and stay right at 195. But when I turn the AC on it seems to come up to 210, now I wasn't on the road for longer than 15 minutes after it warmed up so I didn't really know if it would go any higher or if it was done climbing.

Now I haven't got to test it on the highway, since I don't live super close to a highway. But just driving around at 40-50 seems to sit around 205-207 with the ac on. I did add some sheet metal under the bumper to scoop some air into the radiator while moving.

I'm just a bit lost on what else it could be, think I've tried everything there is, sealed up the radiator, tried bigger radiator, larger more powerful fans, coolant additives.

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Brawndo

· #33 · 10 mo ago

Occam's razor: Water Pump

KJF95S-10

· #34 · 10 mo ago (Edited)

I truly believe the rest of your problem is flow related. Ditch the oreily water pump and get a good stewart warner or edelbrock aluminum pump. The oem style pumps impeller has too much slippage and won't move enough coolant through your thick radiator.

When I finally fixed my trucks airflow issue and it was still running "just a bit too hot" my sewart pump dropped the running temps from 210 down to a steady 185-190. Are you running oem pulley ratios?

Does your intake have bungs to add rear coolant returns? SBC's take really well to that modification.

Joe White

Discussion Starter · #35 · 10 mo ago

KJF95S-10 said:
I truly believe the rest of your problem is flow related. Ditch the oreily water pump and get a good stewart warner or edelbrock aluminum pump. The oem style pumps impeller has too much slippage and won't move enough coolant through your thick radiator.

When I finally fixed my trucks airflow issue and it was still running "just a bit too hot" my sewart pump dropped the running temps from 210 down to a steady 185-190. Are you running oem pulley ratios?

Does your intake have bungs to add rear coolant returns? SBC's take really well to that modification.

Checked on the waterpump today, it is a reverse rotation. It seems to work great. I changed out the thermostat once more to a 180. I didn't build this motor nor put it in the truck. Which I though was a cool thing to not have to deal with, now I am regretting it since I don't know much of the details of the engine. But from the looks I would imagine the pulley is stock as it is a very large one.

It does have the plugs on the back of the intake.

oldeerslayer

· #36 · 10 mo ago

Joe White said:
Checked on the waterpump today. It seems to work great.

How did you determine it works great?

Joe White

Discussion Starter · #37 · 10 mo ago

oldeerslayer said:
How did you determine it works great?

I should say the bearing and impeller seem good, bought a new pump, same one suggested from earlier at oreilys. But after looking at the current one there is no reason to replace it so I put it back on.

Joe White

Discussion Starter · #38 · 10 mo ago

I should add that if I leave the cap off while it is warming up, it does seem to once the thermostat opens the coolant rises and falls quite a bit, my assumption is that is just the thermostat opening and closing, this causes some of the coolant to overflow out the top when this happens. Overheating problems is new to me, so I'm unsure if this is normal.

oldeerslayer

· #39 · 10 mo ago

Might want to look into this pump on Summit.
They say:

Increase pump pressure up to 300 percent
Eliminate steam pockets trapped inside the engine block
Reduce engine temperature by 15-30 degrees

https://www.summitracing.com/parts/gmb-130-1220p/make/chevrolet

Joe White

Discussion Starter · #40 · 10 mo ago

oldeerslayer said:
Might want to look into this pump on Summit.
They say:

Increase pump pressure up to 300 percent

Eliminate steam pockets trapped inside the engine block

Reduce engine temperature by 15-30 degrees

https://www.summitracing.com/parts/gmb-130-1220p/make/chevrolet

I will look into putting that on, as it might help with the problem.

All my tests I've done with this truck has been off highway, on roads that go around 45. So no real highway driving. But today I had to drive 3.5 hours with it on the highway, couldn't go above 65 without it slowly moving back up. The overheating is relative to speed. So it will cool slowly back down under 65, but a lot faster at idle. The radiator shroud I have does have the rubber flaps to help move air through the shroud/radiator at higher speeds.

I did remove the push fan so it is only two pull fans.

The only things I can think of are the waterpump and possible air in the system. If air in the system would cause this type of behavior I will defiantly try bleeding it some more. As replacing the waterpump requires me taking the radiator out due to the limited space.

Just wanted some thoughts as this truck is giving me some major headaches.

Edit: Never thought about this until now, but the possibility that the radiator cap could be bad, I have no clue what type of effect that would cause though.

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