Overheating... SBC 350

[miker]

... I know one thing. I need a set of new ideas

OK, my 2 cents...Timing was mentioned before in this thread. Not sure if you have checked it. If you did check initial timing, have you ever checked the total timing on this engine?

Total timing = initial + mechanical advance + any vacuum advance if the distributor has this capability.

I think it would be worth checking. For a SBC, I think you will find that most recommendations are not to exceed 36 degrees total advance. More than this and it can start to cause preignition/higher combustion temps. You should be reaching max advance at about 2500 to 3000 RPM but this will depend on the springs and weights in the dist and the vacuum advance capability of the distributor, if it has any. BTW, if the distributor is an out of the box component and has never been adjusted, it can be far from optimal.

To me, too much timing makes sense as a possible culprit because you said that in your driveway, running the engine at 3000 RPM it reaches temps of 240 even with a large external fan in front of the radiator. With the engine getting this hot under a "no-load" condition and plenty of fresh forced air, its not surprising that it runs even hotter while actually driving it down the road at the same RPMs.

Easiest way to check total timing is to use a diagnostic or adjustable timing light. With this type of light all you need is TDC marked on the balancer and the TDC pointer in the right location on the engine as your reference. Then have someone run the engine up in RPM and another person continues to dial the timing light back to TDC until you reach max advance. The setting on the light now shows the engine's total advance. A shop should also be able to do this for you as well.

In my opinion, even with your existing 4-row radiator, it should not be running this hot. Since you said its boiling over, I'm assuming that its really getting as hot as your gauge is indicating but you may also want to check the radiator cap to make sure its holding pressure to its psi rating. Stock FJ40 radiator should be using a 13psi cap.

 

[terrx]

I think it would be worth checking. For a SBC, I think you will find that most recommendations are not to exceed 36 degrees total advance. More than this and it can start to cause preignition/higher combustion temps. You should be reaching max advance at about 2500 to 3000 RPM...

Mike, I think it's a good possibility. 36* might be a little high. It has TBI heads which are fast-burn like vortecs and get by with less than older gen1 heads. Maybe 28* to 30* max IIRC.

I wonder if it could be running lean. A lot of things could be contributing. Just a shot in the dark, are the injectors correct for a 5.7L vs. maybe from a 5.0L ? If color code is visible on top of injectors it would be orange/black. Is the ecm broadcast code correct for a 5.7L? Has it ever been tuned or reprogrammed?

 

[jackbrad]

Well.. I don't know much about the timing issues because I have never monkeyed with it. It is electronic ignition since it is a TBI setup.

I will ask around and see if someone can help with the checking of the timing my peeps here can probably help.

 

[jackbrad]

Also, I will check the injectors! Guys, I really really appreciate the feedback.

 

[miker]

Well.. I don't know much about the timing issues because I have never monkeyed with it. It is electronic ignition since it is a TBI setup.

I will ask around and see if someone can help with the checking of the timing my peeps here can probably help.

Ah yes, since its a TBI it is controlled by the computer. I think there is still a base timing that is manually set. I would verify this is set correctly and also verify the total advance just to make sure the ECU is not doing something crazy...

 

[miker]

Have you checked your lower radiator hose to see if it is collapsing under high flow and restricting water? Get one with a spring it it. That has gotten me before...

My neighbor just experienced the collapsed lower radiator hose on the SBC in his '67 impala. Installed a spring and the overheating on freeway issues went away.

Have you checked this jackbrad?

 

[kulangot]

Just pinch it, if you can collapse it, there is no spring.

I would also strongly suggest that you look for a pin hole leak at the top of the radiator. Many thermostat housings have a screw in fitting that is plugged. This is a great place for steam to leak out with out loosing much fluid as it's the highest point in the system. If you are leaking pressure, you will overheat!

Borrow a radiator pressure tester, looks like a bike tire pump, screw onto the top of the radiator. Put it on, pump it up cold and use windex or soapy water to look for leaks. Leave it, on and warm the motor up and see if creates and holds pressure.

 

[Brian in Oregon]

All interesting reading in this thread, even some of the BS.

But, I just don't think these numbers are possible with an automotive type water pump:
6cf/s = 44 Gallons per second or 170 liters per second
8cf/s = 60 Gallons per second or 226 liters per second
10cf/s = 75 Gallons per second or 283 liters per second

Sorry, I typed "second" when I meant "minute". Doh! My conclusion sentence had "minute" in it.

Type once, proof read twice. Obviously I didn't follow that.

 

[jackbrad]

BTW, I did add a spring the lower hose and tested the timing... (Timing was perfect.. Spring changed nothing.) While doing so I hooked up the scan tool to check fuel mixture and eveything is running just fine per the computer.
Just for the fun of it I ran the engine without the thermostat... (No Change)

I wish I had better results to report but, it is still doing the same things. What I can say is that it is very consistent at this point.

Scenario:
Any application of high RPMs (over 2000) will cause overheating. Whether on the highway or in the driveway. It does the same thing every time. No crazy jumps in temp like before the head gasket was bad... just consistently raises the temps are high RPMs until overheat.

Take the RPMs away and it wll slowly recover.

 

[JohnnyC]

I don't recall seeing a shot of the fan shroud from inside the engine compartment toward the front of the truck... Looked thru you whole build thread as well

Is it a full shroud ? Covering the whole radiator? Also how close is the fan itself to the radiator? Under an inch?

 

[Gumby]

Can you see the coolant flowing in the radiator when the t-stat opens?

I have seen water pump impellers fall off or become worn down from cavatation that behave somewhat like what you're seeing. Mostly on BMWs and VWs, but...

or it could be you need a high flow t-stat

 

[warpdriv]

When I built my SBC in my 40 and started wheeling it had problems with over heating. It has a Griffin radiator with contour fans. I was talking with a friend of mine, who is LC mechanic, and he said "I bet your thermostat is not rated high enough." At the time I was running a 180. I had tried no thermostat and a 160. He went on the say that I needed a higher temp one like a 195 because the water is not staying in the radiator long enough to cool down. Here are the steps for cooling to work:

* Motor starts and warms up to temp
* tstat opens hot water in the motor is replaced with cool water in radiator
* Since the cool water from the radiator his the tstat, it closes. Therefore the water stays in the radiator and cools down.
* Once the cool water reaches temp, the process starts over.

So once I put a 195 degree in, problem solved. Hope this helps.

 

[Gumby]

The problem is at highway speeds. It's not fans or shrouds. I'm not seeing t stat, although I'm a big proponent of 195 tstats, especially on FI motors. I'm thinking radiator. Just not enough surface area.

 

[JohnnyC]

he did have a 195 tstat in at one time...and it did it then

IMHO air flow issues

 

[lennyzx11]

I put a 350 into a 72 Vega in the past and had this problem. After fighting through the thermostat, fan clutch, shroud, 4 core radiator, timing and fuel mixture settings, I found that I had installed a new long neck water pump from a small block that had reverse rotation in relation to the serpentine belt set up I had. In short, the water pump was working backwards! There are pumps out there that go opposite rotation and look exactly the same. Changing the pump brought the temps down to 205 idling in 100 degree weather with a 12" electric puller fan.
Lenny (73FJ40)

 

[birdmaninoz]

I have just changed my 2F to a crate 350 without vortec heads and added A/C. I had exactly this problem - it ran much hotter than the 2F round town and went straight up as soon as I hit the highway. We were running twin electric fans on a new aluminium radiator. As soon as it did this the first time I took it straight back to the mechanic. We put back the viscous coupling fan from the 2F, and the original shroud from the radiator. Problem solved.

IT still was hotter than the 2F (but no where near boiling) so I then ceramic coated the headers and insulated the firewall. No more problems on the highway. I also run a bar like yours with Hella rallye 4000s so I thought it was airflow originally - but it now is fine and the best change was ditch the electric fans and use a shroud.

Graham

 

[volcom79]

I went through the same thing for about 8 months. I replaced everything under the hood (hoses, water pump, internal thermostat for 195, new cap, cored radiator for a 3 to a 4 core, added a Mark VIII fan). When I was driving the temp would always jump to around 230. I got so mad one day after spending hours checking everything an reading many post like this I lost it and punch the crap out of the aftermarket gauge that had been installed. Since I broke the gauge I had to replace it, turns out I should have punched that stupid thing first because it was just not reading correctly. Now that its fixed its funny to me and I have replaced everything under the hood. Just a thought because it happened to me. Hope you get it worked out soon.

 

[jackbrad]

Bottomline at this point is we will try another block and heads. I know... crazy.

We will go back through all the tests we can think of before we do but, at this point it appears to be a block problem.

 

[miker]

Bottomline at this point is we will try another block and heads. I know... crazy.

We will go back through all the tests we can think of before we do but, at this point it appears to be a block problem.

You mean a possible crack?

 

[jackbrad]

We don't know but we think the issue is in the block/heads.