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Getting hot at highway speeds -Solved?
- Thread starter AZ79K5Project
- Start date
Thanks @AZ79K5Project. I am wondering if the grill was all expanded metal, would flow better.
I really like the design of the grill. It was my first attempt to weld aluminum. The airflow through the metal itself is surprisingly restricted. I don’t think the aluminum framing has much of an impact. Maybe it does though
I had some woven steel product on my last truck didn't cause me any problems, was pretty heavy duty though.
Need higher percentage of open space vs bars, and/or bigger openings.
Need higher percentage of open space vs bars, and/or bigger openings.
Was your winch on there before you changed the grill? Can you remove the grill easily and test without it? Does your winch cover blow up like a ballon at highway speed? I know, all questions, no answers. Just food for thought...now I’m hungry.
I wonder why the older trucks with the factory spare tire mount up front had no overheating issues ?..seems to me a tire would block more airflow than that custom grille ..
Older engines didn't run as hot and didn't produce as much power.
I had a 74 k5 with a tbi 350 and a th350, and I was having the same problem and I had the same kind of expanded metal grille.
I changed to a 700r4 which dropped my rpms at 65, never overheated after that.
I knew it was the problem because when I kept it at 2500rpm it was fine, when I got to 3000 and up, I could see the needle moving
I switched over to TBI a few years ago and have the TH350. I’m looking for a 700r4 or 4l60 as a replacement but I haven’t found one for a decent price. They’re like gold for some reason and pricey AF. Hijacking my own thread... how hard was the conversion and what did it cost you?
The winch has been on for a long time and never had an issue.
I removed the grill and ran at 3200 RPM for about 11 minutes on a 106 day and the temp stayed at around 215. I can live with that — for now — I think.
bp71k5
3/4 ton status
I’m surprised that grill makes much of an difference. It’s pretty open. I’d be inclined to think some part of the cooling system is “on the edge” and this just helps keep it off of it.
holes are to small, air cannot flow at high speeds is why it is having issues.
I keep meaning to post here, but keep getting busy.
The problem with the grill is a fairly common one in other applications. It all has to do with turbulence. At low air speeds, the air funnels its self through the holes. The air that hits the metal alongside the holes "bounces back" and tends to interfere with the air trying to get through.
At low speeds, the air does not do as much damage. But the faster the air tries to go through, the more turbulence is created, and it interferes with the other air more and more. In extreme cases, you actually have a maximum speed point above which more "suction" does not cause any more air to go through.
In many cases, a solid object blocks less air than a porous one.
For instance, the spare tire blocks the air right in front of it, but the blocked air is free to flow around the tire and can often gain speed doing so. Any turbulence created tends to stay in front of the tire and act as a diverter to funnel the air around. The expanded metal however has thousands of tiny "tires" between each hole and the air never gets a chance to build up a nice laminar flow.
Its easier to see this in fluids, but air acts the same way. At fast speeds, a water pipe that goes from one size to a smaller size gradually can flow as much as two or three times as much water as one that has a abrupt downsize to the smaller pipe. Even though both sets of pipes are the same size.
I used to see this all the time in radio antennas. I would look at a large antenna that had only a few round elements, and tell the guy he either needed to guy the tower or add stronger guys. He would point out that the antenna was mostly empty space, but I still had to help him get the remains off his roof when a thunderstorm came through. Wind loading is a thing.
The best example I could give happened to me and a friend many years ago. Two boats of us were going fishing in a lake. But one of the motors would not crank. I told the other boat to take mine and my friend and I would paddle.
I got a look from my friend, because there was only one paddle.......
The other boat towed us to a good spot, and went on. After a while we decided to move. My friend grabbed the paddle, and we started off. I reached down and grabbed the dip net.
For those of you who do not fresh water fish, a dip, or landing net is round, about 2 feet across, and has holes in it about 1.5 inches across. Obviously very little water resistance. Except, I kept out paddling my friend with the net. He had a nice wide canoe type paddle, and I had an open net, and as long as I moved the net fairly quickly, I was getting more thrust with the net. Move it slowly, and you felt no resistance. Move it fast, and I could not move it any faster due to the load. All due to turbulence.
The problem with the grill is a fairly common one in other applications. It all has to do with turbulence. At low air speeds, the air funnels its self through the holes. The air that hits the metal alongside the holes "bounces back" and tends to interfere with the air trying to get through.
At low speeds, the air does not do as much damage. But the faster the air tries to go through, the more turbulence is created, and it interferes with the other air more and more. In extreme cases, you actually have a maximum speed point above which more "suction" does not cause any more air to go through.
In many cases, a solid object blocks less air than a porous one.
For instance, the spare tire blocks the air right in front of it, but the blocked air is free to flow around the tire and can often gain speed doing so. Any turbulence created tends to stay in front of the tire and act as a diverter to funnel the air around. The expanded metal however has thousands of tiny "tires" between each hole and the air never gets a chance to build up a nice laminar flow.
Its easier to see this in fluids, but air acts the same way. At fast speeds, a water pipe that goes from one size to a smaller size gradually can flow as much as two or three times as much water as one that has a abrupt downsize to the smaller pipe. Even though both sets of pipes are the same size.
I used to see this all the time in radio antennas. I would look at a large antenna that had only a few round elements, and tell the guy he either needed to guy the tower or add stronger guys. He would point out that the antenna was mostly empty space, but I still had to help him get the remains off his roof when a thunderstorm came through. Wind loading is a thing.
The best example I could give happened to me and a friend many years ago. Two boats of us were going fishing in a lake. But one of the motors would not crank. I told the other boat to take mine and my friend and I would paddle.
I got a look from my friend, because there was only one paddle.......
The other boat towed us to a good spot, and went on. After a while we decided to move. My friend grabbed the paddle, and we started off. I reached down and grabbed the dip net.
For those of you who do not fresh water fish, a dip, or landing net is round, about 2 feet across, and has holes in it about 1.5 inches across. Obviously very little water resistance. Except, I kept out paddling my friend with the net. He had a nice wide canoe type paddle, and I had an open net, and as long as I moved the net fairly quickly, I was getting more thrust with the net. Move it slowly, and you felt no resistance. Move it fast, and I could not move it any faster due to the load. All due to turbulence.
Kain
3/4 ton status
i was told not to use this stuff because ^^^ turbulence that it causes.
wont cool right.
wont cool right.
Grill 2.0 built and installed today. I kept the aluminum frame but used steel 1/8 x 3/4 for the veins. I’ll take for a test drive tomorrow. Too hot and too tired to go for a drive.
That looks killer IMO!! I think it will also cool better...
I don't think the holes are too small at all. My grille has smaller, and in the 93-95* days we've had, mine still runs at 185-190 tops.
215 is still too high really. I think something else is still wrong.
If you take the grille out of a factory truck you'll notice some difference in temp. So I think it's not entirely solved yet IMHO.
Here's my grille. Holes are only about 3/8-7/16" square.
I have much less large flat surfaces in it though.
I've seen people use that 3/4" expanded metal before and not have any issues
Kain
3/4 ton status
the triangles create turbulence , why you think gm made square holes in there grilles
bp71k5
3/4 ton status
I don't think the holes are too small at all. My grille has smaller, and in the 93-95* days we've had, mine still runs at 185-190 tops.
215 is still too high really. I think something else is still wrong.
If you take the grille out of a factory truck you'll notice some difference in temp. So I think it's not entirely solved yet IMHO.
Here's my grille. Holes are only about 3/8-7/16" square.
I have much less large flat surfaces in it though.
I've seen people use that 3/4" expanded metal before and not have any issues
View attachment 345658
I tend to agree, but we’ll see I guess.
I already said it in the beginning, the sustained high rpm is the culpritI don't think the holes are too small at all. My grille has smaller, and in the 93-95* days we've had, mine still runs at 185-190 tops.
215 is still too high really. I think something else is still wrong.
If you take the grille out of a factory truck you'll notice some difference in temp. So I think it's not entirely solved yet IMHO.
Here's my grille. Holes are only about 3/8-7/16" square.
I have much less large flat surfaces in it though.
I've seen people use that 3/4" expanded metal before and not have any issues
View attachment 345658
I always have extra transmissions and I had 2 options to connect to the np203, a spacer, which put my np205 in my exhaust where it came together, or the short shaft which I ended up using since I had a core and a rebuild wasn't a bad idea.I switched over to TBI a few years ago and have the TH350. I’m looking for a 700r4 or 4l60 as a replacement but I haven’t found one for a decent price. They’re like gold for some reason and pricey AF. Hijacking my own thread... how hard was the conversion and what did it cost you?
The winch has been on for a long time and never had an issue.
I removed the grill and ran at 3200 RPM for about 11 minutes on a 106 day and the temp stayed at around 215. I can live with that — for now — I think.
The short shaft was under $200.
The spacer was $100, I still have it unopened if you can do this route.
The rebuild could cost anywhere between $500 to $1700, I spent $500.
So it wasn't too bad and you could recover it quick in gas savings.
I do have a core if you want with the spacer, we can make a deal.
Today, I removed the electric fans and went back to the mechanical. On the surface streets, temp stayed at 185. At an extended idle, it crept up to 205, but cooled right down when I increased the RPM. The Flex-a-light 295 seems to work great at idle and great for the AC, but seems to restrict airflow at higher speeds.
I was going to hit the freeway but another gremlin jumped up. My entire AC system shut off and I don’t know why, but it came back on a couple minutes later, and then the engine shut off at two red lights as I came to a stop. It wouldn’t restart for about 3 minutes but then fires back up. I’m wondering if the K&N filter oil seeped or got in the throttle body after I cleaned and re-oiled it today. It idled in the driveway for 15 minutes with neither issue coming back.
I need a blend of the mechanical fans efficiency at highway speeds with that of the electric fans for AC and idle temperature control at super low speed when it’s over 105.
I was going to hit the freeway but another gremlin jumped up. My entire AC system shut off and I don’t know why, but it came back on a couple minutes later, and then the engine shut off at two red lights as I came to a stop. It wouldn’t restart for about 3 minutes but then fires back up. I’m wondering if the K&N filter oil seeped or got in the throttle body after I cleaned and re-oiled it today. It idled in the driveway for 15 minutes with neither issue coming back.
I need a blend of the mechanical fans efficiency at highway speeds with that of the electric fans for AC and idle temperature control at super low speed when it’s over 105.
