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PostPosted: August 20, 2019, 9:30 am 
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Miatav8,MstrASE,A&P,F wrote:
I don't think he needs a bleed. The top row between the tanks leaves very little room for an air pocket. Think of it this way. Imagine every row below the top row was clogged and how the rad would act like a pipe bent into an inverted U.

The shroud may help but it looks like it is not deep enough to prevent blocking flow through the corners and probably will restrict flow at speed. Oems sometimes make shrouds that have poor flow in some areas for clearance reasons but they don't have undersized, thick cores.

To mount the rad, I'd cut the flange off the frame so vertical tabs stick out and drill a hole in each one, then make new L tabs to bolt up to the rad tabs and drill holes in those. Then you can adjust the angle by drilling new holes instead of cutting and welding new frame tabs.

It looks like a lot of the fins are bent that can stop flow. Bugs alone can stop flow on a high efficiency (high fin count) core. If so, use a tiny screw driver to straighten them out.


MV8, the inlet and outlet for the rad are both mid level leaving 1/2 the radiator filled with air if not bled. It appears as if the rad was intended to be mounted with the tanks horizontal, not vertical as it is. Even if fully bled, air will continuously be released from the coolant as it heats and cools. I wonder if a hydronic heating system air bleed fed into the port where the heat sensor is might work as an automatic bleed. A rather unconventional solution I grant you.

I agree with your comment in the depth of the shroud. I would suggest it being at least as deep as the rad core is thick as a starting point. It looks like there may be space for that with a bit of creativity.


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PostPosted: August 20, 2019, 2:10 pm 
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I would go with add-on oil coolers, especially with the heat from the turbo system.

My recommendation is stock RX-8 coolers.
They small and have a built-in thermo bypass, so it's easy to fit and plumb them in.
They're also relatively cheap used.


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PostPosted: August 20, 2019, 5:36 pm 
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I hear what you are saying Chuck and agree that it is best practice to put the upper neck at least as high as the top row, but it can be bled without a hole in the top of the rad. From empty,the system is filled through the expansion tank to minimum, the engine is started to start the pump which fills the pocket due to it's capacity and the delta p across the core, the system is topped, and the cap is installed. The rad would need to create a vacuum to drop the coolant out of the top of the rad.

Many oems have the upper neck lower than the top row as a compromise and no bleed port. 90s Ford explorer and ranger, 02 camaro/firebird, s10, and 02 celica to name a few. The most severe I've seen is the 96 olds achieva but they added a bleed port to that one.

On the oil coolers, the temp differential is much greater between ambient air and the oil than the coolant so the potential temp reduction is much greater plus the radiator capacity is not diminished as much by having to cool the oil too. It will preheat air across the rad if the cooler is mounted directly in front of the rad.

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PostPosted: August 20, 2019, 8:28 pm 
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I am still pondering the root cause here. This setup has worked for years and the only thing that has changed is going from the B16 engine to the b18. They are really similar however the b18 has a block guard that may reduce coolant flow but I dont know for sure.... hummmmmm..

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PostPosted: August 22, 2019, 6:44 am 
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I don't know what you mean by "worked". You've described cooling issues of one kind or another all along since it was road legal in 2015, along with a lot of engine issues that effect power output. Each hp is equivalent to so much btu/heat. You added power/heat going to the b18. If the cooling system was adequate, it appears there was no margin left for a hotter day, more traffic, more aggressive driving in traffic, heavier glycol mixture, slightly improved intercooler efficiency, a little more timing, a little leaner mix, etc.

Coolant flow is mostly determined by the area of the holes in the head gasket and parallel flow through the heater or bypass that bypasses the radiator all the time. The holes in the deck should be larger than the holes in the gasket. The more times the coolant can pass through the radiator core in a given period, the more efficient the core will be. A tiny increase in the gasket holes makes a big difference. The difference in hole size from one cylinder tot the next helps to balance the flow across the cylinders so they cool evenly, but some oems don't stagger the hole size.

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PostPosted: August 22, 2019, 12:28 pm 
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Miatav8,MstrASE,A&P,F wrote:
I hear what you are saying Chuck and agree that it is best practice to put the upper neck at least as high as the top row, but it can be bled without a hole in the top of the rad. From empty,the system is filled through the expansion tank to minimum, the engine is started to start the pump which fills the pocket due to it's capacity and the delta p across the core, the system is topped, and the cap is installed. The rad would need to create a vacuum to drop the coolant out of the top of the rad.

Many oems have the upper neck lower than the top row as a compromise and no bleed port. 90s Ford explorer and ranger, 02 camaro/firebird, s10, and 02 celica to name a few. The most severe I've seen is the 96 olds achieva but they added a bleed port to that one.

On the oil coolers, the temp differential is much greater between ambient air and the oil than the coolant so the potential temp reduction is much greater plus the radiator capacity is not diminished as much by having to cool the oil too. It will preheat air across the rad if the cooler is mounted directly in front of the rad.


I agree with your description, if the delta P in the rad core is high enough to raise the input tank level to the top. I could see a situation where the core flow is less restricted and there might be air trapped. Who knows what really is happening? Of all the OEM radiators that I have seen (I googled cross flow radiators and looked at >100 different ones), I didn't see any on where the I/O ports were mid height and opposite each other. All were with the input at >80% high and the output was @ <20% height, forcing the full use of the rad core and evacuating any trapped air in the radiator as you mentioned.

I am no expert in automotive cooling, but understand some of the physics. Best Practices often are not implemented. Good Enough seems to work most of the time.

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PostPosted: August 22, 2019, 8:34 pm 
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Ok so I tested the shroud... inconclusive but it does tell me that I need to try something else. The radiator and engine seem to match now but the radiator can pull the temp down just keep it steady and it's not climbing at a crazy rate. It took me a while to get the temp up to 215deg. When you consider that its 86deg right now that's not helping either as it will be worse in hotter weather.

Next try... a bigger fan as suggested. On order.

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PostPosted: August 27, 2019, 8:51 pm 
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Geeze this new fan is massive!! Its gonna take me a bit to figure out how to get it to fit.


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PostPosted: August 28, 2019, 11:07 am 
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Looks like you need to mount this as a pusher with the rad in the original position for best fit.
Leave the removable grill in place. Check out my tracker build to see how I mounted mine as a pusher to my condenser.


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PostPosted: September 1, 2019, 5:28 pm 
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Mounted (ish) but not tested. I will try to do that tomorrow. I haven tried to put the nose cone on with those mounting brackets hanging out in space but I'm pretty sure the top of the nose cone is going to hit the top of the fan. :?

I'm also curious to see if this thing will push more air than the old one. It doesn't seem so but I don't want to make any assumptions until I actually heat the car up.


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PostPosted: September 2, 2019, 3:49 pm 
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Tested. Bare with me because this is kind of hard to explain So, the engine is still getting too hot for my liking and I can heat her up no problem just getting on and off the gas in the garage. If the engine is hot like 210deg and you let the car idle, the fan will pull the temp down at the radiator to 190ish but it only slowly pulls the engine temp down to around 206. If you Rev on it hard again the radiator temp goes right back up. So I'm not quite sure what to do. I'm testing in pretty hot weather too. 97deg outside.

Also this is reason one and two why you don't stand next to exhaust when you're revving the car up and down

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PostPosted: September 2, 2019, 5:21 pm 
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Your expectations seem pretty high. It isn't unusual to have cooling issues with big/powerful engines in tiny cars, especially revving them up while sitting still in an enclosed space.

Make sure you wired the fan with two positive wires for high speed.
Step up to an air to oil cooler. :cheers:

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PostPosted: September 2, 2019, 7:01 pm 
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Yeah the fan is set on high unless it's not getting enough power for some reason. You think an air oil cooler would be better than the stock coolant oil cooler? Or even a secondary pump?

I can also try a dual pass radiator.

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PostPosted: September 2, 2019, 7:06 pm 
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An air:oil cooler will for sure be better than a coolant:oil one.

Again, I recommend stock RX-8 ones with the built in thermo-bypass valves. Easy to locate, and relatively cheap.


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PostPosted: September 15, 2019, 7:43 pm 
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I was hoping to take her to a small Track by the office on Friday. Any suggestions on an oil cooler? Should I also try to run just straight water or some sort of racing coolant?

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