Technical SBC 350 Getting Hot on Highway

Got a situation that has me a bit baffled looking for ideas.

Recently swapped radiator in '61 Impala with a oversized 2 core aluminum Cold Case with 2 11" electric fans and shroud.
The issue that I have run into is it will get hot at highway speeds or underload, going up hills and running the a/c also while on the highway, however, it will sit in traffic all day, cruise a around a show, idle in the garage and never have an issue. It has never gotten so hot to puke or blow by the cap.

Things I have tried and details.

• Originally had a 160 thermostat and the temp would swing from 180-220. Fans would shut off when gauge showed 180 and temp would go up, fans come on and it would start dropping. . It would do this over and over again while sitting in the garage with and without a/c running Fans never shut off going down the road
• Changed to a 180 and it idles at 200 and will get up to 220 under load. Fans come on and never shut off, temp never goes below 200 on gauge. Seemed like a/c didn't have as much impact on using 180 thermostat vs. the 160 but I may be imagining that.
• Fan sending unit is on at 185, gauge shows 200 when they come on
• Gauge sending unit is located in stock GM location in the side of the drivers head. Gauge is a classic instruments hot rod 2 1/8" gauge. Nothing special.
• The lower hose is not collapsing with RPM
• High flow water pump. It's a PRW 1435001 aluminum pump.
• Timing is using vacuum advance. Initial of 2ish, 16ish w/vacuum and 34ish total so in the ball park.
• 13lb radiator cap

I have another gauge and sending unit coming to confirm one or the other maybe having an issue.

Is there something I am missing or another suggestion of something that I should be looking into?

 

how about some pictures? maybe we can see something obvious about airflow, etc that you have overlooked

 

Sounds like you don't have enough radiator. You may need something with more heat rejection capacity, especially under load when the engine is generating much more heat than at idle. May need to look at a 3 or 4 core unit, or a proper brass and copper rad.

That said, if it is running at a constant 200 deg, under load, on the warmest day, I probably wouldn't worry about that unless you are running into fuel vaporization issues. As Squirrel alluded to, pics would defiantly help. Electric fan setups can also be detrimental to air flow at highway speeds, and they may be the source of your perceived problem.

 

I was thinking that two 11" fans with proper shrouding will be covering up half of the radiators surface....

 

I'd try to verify you're getting full timing over 50 with mechanical and vacuum added in under part throttle cruise.

Also maybe rule out timing chain slack. If the cam is retarded due to slack, some people twist the distributor to set the ignition timing, which doesn't resolve the late exhaust event issues. Probably not the entire issue, but a good one to rule out.

-rick

 

What's the entire story? You've had the car for years and decided to swap to this new aluminum radiator and it doesn't work right or it was over heating before that? New build? Did it ever cool right? Was anything worked on before the issue?

-rick

 

2nd what Squirrel said. Pic would help but I bet you’ve blocked half the radiator with the new shroud.

 

To add to the above. Did you install a new lower radiator hose? Is it possible that it’s collapsing (sucking closed) at higher rpm’s?

 

I would first verify temperature with a mechanical gauge. Since you aren't pushing any coolant, it might be normal with your setup. Pictures would really help.

 

I agree with Squirrel about the shroud covering half the radiator. But even without the shroud covering half the radiator would two 11" electric fans be enough to cool that radiator?

 

I failed to mention that it cools itself off coasting downhill or off throttle conditions. The 160 thermostat it would cool off quick, the 180 it cools off a bit slower.

Also that I have one of those power probe mutimeters that has a thermocouple attachment. I stuck it through the top and did my best to get it as close to the upper hose inlet as possible. The water temp was reading 175-185 depending on what I was doing with the motor.

The 2 fans and shroud basically covers up the entire back of the radiator. I considered adding the flaps into the shroud but probably could only get 2 maybe 3 in it.

Previously it had a 4 core aluminum, have no clue what it was as it came in the car but it visually looked like a Summit brand. It had the stock bolt on fan and shroud + a 16in electric mounted to the back of the rad that was used for traffic or if the a/c needed it. Issue it had was it would get hot in traffic or cruising around shows. You couldn't use the a/c hardly at all in traffic.

 

I don't understand 2 degrees initial timing and 34 degrees total.
Does your distributor actually provide 32 degrees of mechanical advance?

 

If you didn't have this problem with the old radiator, I'd have to suspect the new radiator.
Why are you using the high volume water pump on a street engine?
Just some thoughts for discussion.

 

It has vacuum advance and with that its at around 16 and then 34 total unless I'm missing something.

 

The problem was in reverse. It would get hot in traffic and with the a/c running but didnt going down the road.

 

Can you remove the fans and shroud and go for a drive on the highway?

Your total timing doesn’t include vacuum advance as you’ll not have any vacuum advance at high throttle /rpm

 

My first thought was the same as your’s Phil, why 2* initial? Crank up the initial to 8-10* and see what happens. Your initial + distributor + vacuum advance should be in the low 50’s at cruising speeds. Give it a try, won’t cost anything but a little time.

 

I had a similar problem with my 41. Although it did not have A/C. Turned out that the mechanical advance on the distributor was not advancing at hiway speeds. Changed up the distributor, problem solved. All the best. Snowman ⛄️

 

Here comes an argument....Does your High Flow water pump not allow coolant to stay in the radiator long enough to dissipate enough heat before re-entering the engine? This would be exaggerated at highway speed.

 

No, because it transfers heat faster, as the temperature differential is higher. Go back to your Heat Transfer text book, look up the equation again....

 

Is the water pump the correct rotation for your setup? There are CW and CCW rotation pumps.

 

Staying only within High Flow Pumps. I’ve experienced thermostat shutting due to excessive flow. But that another thing all together.

 

Ok so help me understand because this was a confusion point for me. I had to replace the vacuum advance and that was a first for me. So when the advance is unhooked I have it at roughly 2-4 degrees advanced. Connected to the advance its at 16 and at RPM its at 34. I didn't think you wanted anything above 36 hence the reason to start out at 2-4 degrees advanced.

 

Based on what you just said. Is this your vacuum line to the distributor? If it is it’s currently hooked up to full vacuum. Typically it’s connected to the other port located on the left face of carb.

 

Yes that line goes to the advance on the distributor.

 

That is why the timing goes up from or 2-4 to 16. Hook the line to the port on the left instead and bring initial timing up to 12 as a starting point.

 

34 to 36 degrees is at wide open throttle.
At no load cruise highway speeds, timing should be at least above 40-45 degrees or maybe even more.

That would be let say 10 degrees initial, 20 degrees mechanical advance and say 15 degrees of manifold vacuum from canister. That would be 45 degrees.

I would put 10 degrees of initial timing in it, hook vacuum advance to manifold vacuum and go drive it at highway speeds.

Bill

 

The master cylinder probably needs to be topped off.

 

If it's heating up in traffic, that's usually an airflow issue. At highway speeds you're creating more heat as the engine is working harder, but have the airflow to get rid of the heat. It sounds like your new radiator isn't transferring heat out effectively at highway speeds. Did you flush the engine block?

 

The engine will like having 34 degrees timing at higher RPM, with the vacuum disconnected. This is what's usually referred to as "total advance". But when you connect the vacuum advance, it will go up to around 50 degrees. This only happens at part throttle, not at full throttle, and the engine will be fine this way.

so maybe just advancing the timing will help the cooling issue.

What I would do is disconnect and plug the vacuum advance hose, then rev the engine up to 3000 rpm or so while watching the timing, see if it gets up to 34 degrees. If not, then advance the timing (rotate the dist housing) until it does. Then reconnect the vacuum advance, and go for a drive. You will probably have to reduce the idle speed.