SBC 350 Overheats

4434 Views 86 Replies 12 Participants Last post by Joe White, 7 mo ago

Joe White

Discussion Starter · 11 mo ago

3

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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crazy_ate

· #41 · 9 mo ago

Joe White said:
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.

What happens when you drive a car with a bad radiator cap?
Because the engine depends on the heat absorption capacity of the coolant in the radiator when you drive a car with a faulty radiator cap the car will overheat. The car overheats because the pressure I the radiator is too low for it to contain all the heat generated by the engine. Symptoms of a bad radiator cap [How to test and Fixes] | Rx Mechanic
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Also make sure your coolant to (distilled) water mixture/ratio is correct and no air pockets in the system.

KJF95S-10

· #42 · 9 mo ago (Edited)

Yeah try a new cap. I've never really seen them go bad but it could happen I guess. Air in the system is highly unlikely in an sbc, its very hard to trap air in a forward flow cooling system as it naturally bleeds. Ideally the thermostat housing should be the highest point in the cooling system.

If you're overheating at highway speeds you definitely aren't circulating coolant well enough. Airflow just isnt an issue at 65 mph. Seems like flow is dropping off dramatically below a certain rpm.

This is what I meant for the coolant returns, not mandatory by any means but it does help give hot coolant at the rear of the heads a way out.

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Joe White

Discussion Starter · #43 · 9 mo ago

KJF95S-10 said:
Yeah try a new cap. I've never really seen them go bad but it could happen I guess. Air in the system is highly unlikely in an sbc, its very hard to trap air in a forward flow cooling system as it naturally bleeds. Ideally the thermostat housing should be the highest point in the cooling system.

If you're overheating at highway speeds you definitely aren't circulating coolant well enough. Airflow just isnt an issue at 65 mph. Seems like flow is dropping off dramatically below a certain rpm.

This is what I meant for the coolant returns, not mandatory by any means but it does help give hot coolant at the rear of the heads a way out.
View attachment 366278

I'll go buy a new cap. I bought the pump from Summit Racing, I don't have a place to work on it at the moment so I'm unsure when I'll have time to go change it. But it would make sense at higher speeds that the impeller could be slipping on the shaft. I feel stupid for not checking that, I kind of just looked at it, and it didn't look that old so I didn't even think about that being a possibility.

The cap could very well be the problem though, I noticed that the overflow tank has not changed a bit since I put new coolant in it the other day. Which is defiantly wrong because I know there has to be some air left in the radiator. Almost impossible to fill it completely when the level goes up and down and overflows coolant out of the fill neck.

Joe White

Discussion Starter · #44 · 9 mo ago

Well, I call it fixed I guess. don't think there is anything else to replace. I put in the new waterpump, still gets warm on highway. Before the waterpump I was only able to go 65 mph at around 205F, (180F thermostat still) now with the new pump I was going 70-75 mph at around 198F, but slowly..slowly..slowly climbing up. So after 30 more minutes it could've gone to the old temp. Both days I've driven it on the highway, same route. Both days a cool 75-80F outside. I've spent wayy to much on a simple problem.

S15E83

· #45 · 9 mo ago

In post #25, you’d mentioned “struggling to start and idle.” That, plus the overheating, has me wondering if the timing is too far advanced. That would be worth checking.

A flow issue could also be a block issue, especially if a PO used Barr’s or some other miracle in a can, and there just isn’t enough water moving through the engine. Might be worth doing a couple of flushes.

Sent from my iPhone using Tapatalk

Joe White

Discussion Starter · #46 · 9 mo ago

S15E83 said:
In post #25, you’d mentioned “struggling to start and idle.” That, plus the overheating, has me wondering if the timing is too far advanced. That would be worth checking.

A flow issue could also be a block issue, especially if a PO used Barr’s or some other miracle in a can, and there just isn’t enough water moving through the engine. Might be worth doing a couple of flushes.

Sent from my iPhone using Tapatalk

I believe your not wrong, I think there is something with the flow wrong, so I need to flush it some more. Timing is not set correctly I'll add, but I have adjusted it far from what it has been right now and no change. But both need taken care of, harmonic balancer is off, so it isn't as easy to set timing since I have to set another TDC.

I've been looking into sending it into a shop for them to take a look and perform those two things. Only one that was willing is 2 weeks behind, but obvious something is wrong, because it was 77 out today, at night, and it was overheating.

Thank you for the response.

oldeerslayer

· #47 · 9 mo ago

You've been driving it w/o a harmonic damper?

Joe White

Discussion Starter · #48 · 9 mo ago

oldeerslayer said:
You've been driving it w/o a harmonic damper?

It has one, it is just obviously offset. Correct timing on it shows around 70 degrees after tdc. I tried setting it on the dampener at 34/36ish, still after tdc, but the engine would spit out the throttle body, when trying to accelerate.

eshaw

· #49 · 9 mo ago (Edited)

The first things I noticed about your cooling are the very thick core of the radiator, I think more than likely it may be contributing to your issue. I don't care for the spiral hoses either, I prefer the molded ones as they don't affect the flow. Double check your belt routing. Your timing can also be an issue from what I've read here. Removing the pusher fan was a good idea, all it does it block air flow. The pullers looked to be marginal also. Going to the Intrepid setup is a step in the right direction, just make sure they're wired correctly and seal to the radiator with a proper shroud. You've sealed up the radiator to the support so that's good. Not knowing how the core was constructed it's hard to say what's going on there, single tube is way better than multiple tubes.

KJF95S-10

· #50 · 9 mo ago

Hard starting is usually related to lack of amperage. That same lack of amperage will cause the E-fans to not run at full speed. You will see them running and never be able to tell the difference. This happened on my Sonoma. Incredibly difficult to start and overheated. The issue was not enough grounding. Literally adding a ground strap fixed everything at once. I would check your electrical very well and make sure it's 100%, if it's not your fans will run slow and you will overheat.

Joe White

Discussion Starter · #51 · 9 mo ago

KJF95S-10 said:
Hard starting is usually related to lack of amperage. That same lack of amperage will cause the E-fans to not run at full speed. You will see them running and never be able to tell the difference. This happened on my Sonoma. Incredibly difficult to start and overheated. The issue was not enough grounding. Literally adding a ground strap fixed everything at once. I would check your electrical very well and make sure it's 100%, if it's not your fans will run slow and you will overheat.

The hard starting issue probably has to do more with timing if anything else just the tune with the holley sniper. Cranks over fast and fine. I don't remember if I mentioned I installed a new set of dual derale electric fans, that push out 3700cfm. Problem with intrepid fans is that they wont fit in the engine bay, they are too thick and will hit the pulleys. I installed a new set of wiring for those fans. Only other thing besides timing and coolant circulation is heat not leaving the engine bay properly, but I would think at highway that's just not a problem.

Only problem that I cant test is to see if the radiator is actually cool while the engine is overheating. The ac condenser covers the front of the radiator, so I can't get an accurate reading of how hot the radiator actually is.

KJF95S-10

· #52 · 8 mo ago

I still have airflow issues with mine even with the cooling system working perfectly. The cramped s10 engine bay with a V8 is known for not letting hot air out. You may need to remove the lower portion of your inner fenders and run a cowl hood if you don't already. Gotta remember the 4.3 had a nice gap between the engine and radiator to expell air and the V8's don't have that luxury.

Rhotpursuit

· #53 · 8 mo ago

KJF95S-10 said:
I still have airflow issues with mine even with the cooling system working perfectly. The cramped s10 engine bay with a V8 is known for not letting hot air out. You may need to remove the lower portion of your inner fenders and run a cowl hood if you don't already. Gotta remember the 4.3 had a nice gap between the engine and radiator to expell air and the V8's don't have that luxury.

Where are you getting your information? There are lots of V8 conversions running around out there that haven't hacked up the inner fender and run fine. I've driven mine in 115* heat with the air on and it doesn't overheat. Do you know how a cowl hood works? High pressure at the base of the windshield pushes air in to the engine compartment, not let it escape.

Joe White

Discussion Starter · #54 · 8 mo ago

Well it cant bee too hot under the hood. Just thought about it and my MAT showed around 95 or so. and its a good 90 outside. I do have a cowl hood that brings in some fresh air, but if it wasn't escaping it probably wouldn't be so low. Now on a day like this opening the hood will help it cool off faster. But it doesn't fix the problem, I tested that during the summer when it was like 105 out and it still overheated. More than likely just timing and water circulation. Still waiting on a shop to call me back, since I don't have a area to work on it myself currently. But those are the two things I'll advise them of.

Edit: I say faster.. not really much faster, maybe takes one or two less minutes to go down 10 degrees

KJF95S-10

· #55 · 8 mo ago

Rhotpursuit said:
Where are you getting your information? There are lots of V8 conversions running around out there that haven't hacked up the inner fender and run fine. I've driven mine in 115* heat with the air on and it doesn't overheat. Do you know how a cowl hood works? High pressure at the base of the windshield pushes air in to the engine compartment, not let it escape.

My information comes from personal experience. Yes I'm familiar with how cowl hoods work. Not sure if you've seen one in use before but at idle radiant heat pours out of the cowl, trapped heat, and as you know heat always rises. That heat would otherwise be sitting in a layer under your stock hood festering and heatsoaking everything.

Yes air is being forced into the engine compartment but if it has nowhere to go (it will be forced downward) you don't get a cooling effect, you get the exact opposite. Trapped air from cowl induction has caused race cars to actually lose downforce and lift the front ends off the pavement if there is inadequate airflow through the compartment. They are a huge benefit but only if the air has somewhere to exit.

I'm not a proponent of hacking up inner fenders, I hate it in fact. But you need some means of ventilation when you have a physically larger engine making 2 or 3 times as much power as the weenie 4.3. It's going to generate more heat. Period

Rhotpursuit

· #56 · 8 mo ago

How do you explain my lack of heat problems? My engine compartment is pretty full. And I do have a cowl hood. I have taped a strip of paper to the hood above the cowl. At about 10-15 mph, it gets sucked to the vent.

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Joe White

Discussion Starter · #57 · 8 mo ago

Rhotpursuit said:
How do you explain my lack of heat problems? My engine compartment is pretty full. And I do have a cowl hood. I have taped a strip of paper to the hood above the cowl. At about 10-15 mph, it gets sucked to the vent.

View attachment 367431

Thats what I really need, a plastic piece like you have where your hood latch is. Not sure how to find what its called though. Not sure it will really help the problem, but will make the engine bay nicer.

Rhotpursuit

· #58 · 8 mo ago

Joe White said:
Thats what I really need, a plastic piece like you have where your hood latch is. Not sure how to find what its called though. Not sure it will really help the problem, but will make the engine bay nicer.

Isn't that part of your grille? You might try the junkyard.

Joe White

Discussion Starter · #59 · 8 mo ago

Rhotpursuit said:
Isn't that part of your grille? You might try the junkyard.

Never had one on it when I got the truck. Someone probably just took it off and never put it back on.

Rhotpursuit

· #60 · 8 mo ago

Find a pic of a 98 grille and compare it to yours. It looks like your grille has been modified for whatever reason, and the part on mine you're looking at has been removed. I believe they were all one piece from 98+

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