Another 350 V8 Cooling Thread - Questions. (1 Viewer)

[RWBeringer4x4]

Hey everyone,

Last year I installed a new 350SBC into my 1975 FJ40 to replacing a tired/failing 283. This recent heat wave on the east coast has given me a good chance to torture test it. I wanted to share my finding and get opinions on whether this is good, bad, or ugly.

First - my setup:

- Bone stock, 195 horsepower small block.

- 7-blade, 18 inch fan with (very) tight shroud (about 1/2” clearance). Fan is rigid/belt-driven - no clutch, no flex. It sits about 1-1.5” from the radiator.

-190 degree thermostat

- stock late model FJ40 radiator (CFS OEM knock-off). 4-core brass and copper

- timing 12 degrees advanced at idle

- standard water pump

OEM Toyota temperature sender adapted to Chevy threads through adapter coupling and mounted in stock Chevy location (driver’s side head under exhaust manifold).

Everything is new, installed last winter.

As for temperatures - everything runs plenty cool while moving, it gets a bit too hot for comfort at idle.

This was taken over the weekend when it was about 97 degrees outside with no wind, after idling for about 30 minutes:

According to the excerpt from the manual below - the third hash mark reflects 210 degrees - so honestly, I wouldn’t normally be that concerned as that’s within the realm of reason for a small block.

However, an IR thermometer told a different story when measuring spots around the engine.

While the gauge was at the third hash mark:
Cast iron Heads: 225-230 degrees
Cast iron block: 220 degrees
Cast iron water pump: 220 degrees
Upper radiator hose: 215 degrees
Top of radiator: 220 degrees
Bottom radiator hose: 185 degrees

Test 2 - today; 90 degrees; idled for 1 hour.

- Heads/block/water pump: 212-215 degrees

Upper radiator hose: 200 degrees
Lower hose: 175-180 degrees
Top of radiator: 210 degrees

Questions:
- Is it normal for the block/heads to be radiating heat warmer than the coolant flowing through it?

- which measurement do I trust - the gauge (showing slightly under 210) or the IR thermometer - and if the thermometer, which location is the best measurement to rely on? Seems like the temperature measured at the upper radiator hose is closest to what’s reflected on the gauge, but the cast iron is substantially hotter.

- It seems like my current setup can handle keeping the engine temp about 120 - 125 degrees over ambient air temperature. So if it’s around 70 degrees out I shouldn’t have too many issues. Anything hotter and my temperature at idle starts to creep up if I’m not moving.

- temperature drop through the radiator seems to be about 20 degrees based on upper and lower hose measurements - is that normal?

Obviously this is all a bit hotter than you’d want but it’s under the worst case scenario - sitting at idle for very long periods of time. By this math it would need to be ~110 degrees outside before I boiled over... is it worth looking for ways to improve cooling or is this “good enough?”

 

[coonassjohn]

Find another spot and install another non-Toyota temp gauge as a back-up. 210 at the upper part of the rad. seems ok for a long idle with little airflow. My 350 will do the same thing on a long idle, but quickly returns to around 190 when I start moving. I have the stock temp sensor and a separate Stewart-Warner mechanical gauge installed.

 

[coonassjohn]

As far as the IR thermometer it's also picking up the ambient heat under the hood as well as what you are trying to measure.
Leave it in the tool box for this exercise.

 

[RWBeringer4x4]

Fundamentally I think I agree with you - although I haven’t ponied up for a second temperature gauge yet.

Similar train of though - how do you feel about 1/2” of fan clearance with the shroud. I haven’t had a problem yet but I worry about when off-camber or flexed off-road.

To me the temperature gauge and an IR thermometer on a matte black surface (best response) that is the coolant hose seem to agree with each other - if the third hash mark is 210 as the manual implies.

It also (at least logically) stands to reason that the cast iron components will retain heat longer than the hose and thus read a bit higher, and perhaps run a bit higher than the coolant carrying the heat away.

I guess I’m mostly just looking for reassurance that if I ever get stuck in traffic or wind up sitting for a long time at idle (happens a lot 4 wheeling) that I won’t fry something. Seeing my heads at ~230 makes me worry, but the radiator hasn’t boiled over...

 

[workingdog]

I also suggest a quality temperature sensor, I think there's a port on the opposite side of the other head. None of those temps scare me, you're getting 185 back into the block, that tells you you're okay - I think.

 

[coonassjohn]

Water temps are the main indicator for overheating and your numbers seem fine. No offense but you are science f+++ing this issue way too far. As for the fan clearance you can always use a slightly smaller fan. I have an aluminum radiator and it also helps to dissipate the heat. I also have around a 1/2 in. shroud clearance with no problems.

 

[RWBeringer4x4]

Water temps are the main indicator for overheating and your numbers seem fine. No offense but you are science f+++ing this issue way too far. As for the fan clearance you can always use a slightly smaller fan. I have an aluminum radiator and it also helps to dissipate the heat. I also have around a 1/2 in. shroud clearance with no problems.

I’m a scientist by profession - science f+++ing is what I do!

I guess I was just expecting it to sit right at 190 if everything is working right - but maybe that’s asking a lot.

I actually started with a smaller 17” fan and went to the 18” to see if there were cooling improvements - there were, so if o can keep it without eating the shroud I will.

 

[workingdog]

No, not 190. I'm not sure what engine you have, but 210 is not a problem at all. For a newer engine 220 is okay. Not forever, but for long as the engine is under significant load.

The science is - you want the engine hot (like 220) and the incoming air cold for better combustion.

 

[RWBeringer4x4]

No, not 190. I'm not sure what engine you have, but 210 is not a problem at all. For a newer engine 220 is okay. Not forever, but for long as the engine is under significant load.

The science is - you want the engine hot (like 220) and the incoming air cold for better combustion.

It’s a gen 1 flat tappet 350 - 195HP truck variety.

Yep 210-220 don’t worry me other than that they’re above the thermostat set point - but even then I’m not majorly concerned. The bigger worry was that I was seeing 230ish on the cast iron parts - that might be normal but wasn’t what I expected.

 

[coonassjohn]

I’m a scientist by profession - science f+++ing is what I do!

I could tell by your post.

 

[SteveH]

My IR temp gun read 15 degrees higher when the engine was running and the hot fan air was passing over the sensor (than it did when I turned off the engine). Not sure if your engine was running when you were taking its temperature, but consider shutting it off first.

 

[pb4ugo]

Your t-stat is a 195* so temps aren't really going to go below that or have large swings from cooler to hotter or vice versa. A lot of FI engines are required to run in the 210*+- mark to make their computers happy. In the past when I was running high hp engines my concerns for high temps were in the 235-240 range. For the last couple of decades I have run a 160* t-stat, so I see large swings in my temps. Highway around 180-190 maybe 200, On Trails long up hills it climbs up to 200+, downhills 160-170. 230 cast temps seems logical, your not going to get 100% heat transfer. When rpms go up, there's more water flow and air moving thru the rad= cooler temps. When I went to ramshorns my running temps did increase. Typically, immediately after the engine is turned off, you will get a slight temp spike, because water flow is stopped. What you describe sounds OK. Are you using a 50/50 mix antifreeze?

 

[workingdog]

Well, as a scientist, how can you live with the stock temp gauge and no number? I get frustrated by the real gauges because you can't tell enough detail. If you engine is OBD, then get one of those gauge things that plugs in. There are a couple pretty cheap, and then you'll know exactly what the ECM is seeing. That's the data you need.

 

[RWBeringer4x4]

Your t-stat is a 195* so temps aren't really going to go below that or have large swings from cooler to hotter or vice versa. A lot of FI engines are required to run in the 210*+- mark to make their computers happy. In the past when I was running high hp engines my concerns for high temps were in the 235-240 range. For the last couple of decades I have run a 160* t-stat, so I see large swings in my temps. Highway around 180-190 maybe 200, On Trails long up hills it climbs up to 200+, downhills 160-170. 230 cast temps seems logical, your not going to get 100% heat transfer. When rpms go up, there's more water flow and air moving thru the rad= cooler temps. When I went to ramshorns my running temps did increase. Typically, immediately after the engine is turned off, you will get a slight temp spike, because water flow is stopped. What you describe sounds OK. Are you using a 50/50 mix antifreeze?

Yep, 50/50 antifreeze. And that heat soak temp spike is what I was worried about with the cast iron temperatures. I don’t want to be “borderline” at idle then have it heat up and crack/warp something after I shut it down...

Well, as a scientist, how can you live with the stock temp gauge and no number? I get frustrated by the real gauges because you can't tell enough detail. If you engine is OBD, then get one of those gauge things that plugs in. There are a couple pretty cheap, and then you'll know exactly what the ECM is seeing. That's the data you need.

I couldn’t live with it - this snooping around with an IR gun. Turns out the OEM gauge, while not particularly descriptive, is reading accurately.

My engine is carbureted and not OBD at all - no ECM to tie into.

 

[archie73]

So here’s one more bit of input to screw this up some more:
My mildly built 350/stock rad/Taurus fan never overheats around town, highway, crawling or giving it offraod. BUT when I drive up a 3 mile 10% grade(commute) I need to pull over halfway and cool down for a few minutes. I can see the fan get switched, usually drops 10-15*. Ambient air temp doesn’t seem to affect it much.
As far as the stock gauge goes, that 3/4 mark is about where I get concerned. I can see the fan get switched, usually drops 10-15*. Much past the 3/4 mark and I’m puking antifreeze.
I’m going try a new radiator cap, but there’s an ls in the garage waiting to go in...

 

[RWBeringer4x4]

So here’s one more bit of input to screw this up some more:
My mildly built 350/stock rad/Taurus fan never overheats around town, highway, crawling or giving it offraod. BUT when I drive up a 3 mile 10% grade(commute) I need to pull over halfway and cool down for a few minutes. I can see the fan get switched, usually drops 10-15*. Ambient air temp doesn’t seem to affect it much.
As far as the stock gauge goes, that 3/4 mark is about where I get concerned. I can see the fan get switched, usually drops 10-15*. Much past the 3/4 mark and I’m puking antifreeze.
I’m going try a new radiator cap, but there’s an ls in the garage waiting to go in...

So according to above, 3/4 mark is “only” 210 degrees. Which the IR thermometer seems to confirm for the most part. The toyota manual suggests that the 4th mark should be the boiling point...

 

[workingdog]

That sounds about right.

 

[terrx]

....
I wanted to share my finding and get opinions on whether this is good, bad, or ugly.
....

Somewhere between bad and ugly IMO. I'd cut that 7 blade fan down to 16", add a fan clutch and good shroud, and put a larger aluminum radiator in front of it. Also invest in real gauges.

 

[reddingcruiser]

Opinion Alert!
Stop the frustration and put in a radiator that is actually designed to cool an SBC. Set it up with a fan shroud, a 7 blade OEM fan (69 to 74 Camaro) and clutch.

 

[RWBeringer4x4]

Somewhere between bad and ugly IMO. I'd cut that 7 blade fan down to 16", add a fan clutch and good shroud, and put a larger aluminum radiator in front of it. Also invest in real gauges.

What’s wrong with the existing shroud and what makes for a “good” shroud?

I’ve got a 16” 6-blade (clutchless) fan and the cooling situation was actually a bit worse (stands to reason). I guess with a bigger radiator it could potentially be sufficient.

Opinion Alert!
Stop the frustration and put in a radiator that is actually designed to cool an SBC. Set it up with a fan shroud, a 7 blade OEM fan (69 to 74 Camaro) and clutch.

I’m not necessarily frustrated - I just did some extra homework in the engine bay - mostly to correlate what I thought the (pretty nondescript) gauge was telling me and actual temperature. Really was mostly trying to figure out which IR reading was most accurate to compare to the gauge.

I tend to agree with the folks above that as long as the third hash is 210 degrees I don’t have a problem 98% of the time, as long as engines really only care about the COOLANT temp and not the BLOCK temp. Just not sure at which point a block gets hot enough to crack or a head gasket decides to give up.

As long as the truck is moving at all it stays below 200. It’s just prolonged idles on 80+ degree days where I see them temperature creeping up to the third hash. I don’t believe I’ve ever seen it go BEYOND the third mark.