I wish i could start a build and drifting. It looks like more of a lifestyle then just a hobby. Unfortunately i dont have a garage either. GLWB really makes me happy to see such a nice car. Total D SPEC

Attachment 663438

Attachment 663439

Attachment 663440

Had a blast on the Streets of Detroit (MDU RD 3), qualified 13th and finished 14th. Could have done better, but we keep struggling with the rear mounted radiator setup. :(

Not sure if anybody has any ideas here, but here are some of the facts:
- ISSUE: engine randomly overheats while idling
- OBSERVATIONS:
* Air accumulates at high point on engine (neck coming off water-pump out where we have a bleeder valve)
* Air does not accumulate when drifting (engine is being revved, while it's not overheating)
* Spark plugs are always black, which does not indicate blown coolant seals
* We bleed the system multiple times, many different ways, tried every method
* When we use the front bleeder valve every minute to get the air out that accumulates, the car never starts overheating
* When overheating occurs, radiator pressure seems to increase and water flow is reduced, causing for water to not flow through 90% of radiator area... also causes water to overflow past pressure cap (24psi)
* Engine runs great and doesn't overheat when this issue isn't happening
- POSSIBLE PROBLEMS:
* Blown coolant seals
* Trapped air pockets at other high points
* Air being sucked in through vacuum?
* Water-pump blades create air bubbles at low rpm (like a boat propeller)

Any input will be greatly appreciated, thanks! :nod:

Thats a tough one man....... where are the radiator coolant feed lines located on the rear mounted radiator? if it's fine while driving and only overheats at idle then maybe its a flow problem...but that doesnt explain the air. There shouldn't be any air in it. Do you have a lisle funnel? Are you using pure water? or a coolant mix? If you throw some coolant in there and your motor is sucking the coolant you'd smell the sweet smells of disaster.... hmmm... But I think theres probly just air trapped in the system... after all...you have added quite a bit of capacity to the system as a whole..

Dude I just saw pics of your coolant routing.....looks VERY well thought out. I think you just need to spend some more time bleeding it. Randomly overheating at idle kinda shouts either Hot air pockets passing your coolant sensor....which would be a definite cause your needle to jump. ORRRR...... The motor isn't spinning fast enough to move your water pump fast enough to move the hot water away from the coolant sensor. If your not adding water/coolant....rule out the coolant seal problem for the time being. But I say keep adding water till capacity is reached.

You could try Turning up your idle... where is it idling at right now? It's a track only car nah?....try raising it to say 1300. See if the problem persists.

Hmm, I like the idea of a higher idle... I will try it at this next event. Currently it's idling at 800 rpm, kinda low I know. I am running distilled water with Redline water wetter.

So let me tell you how we ended up getting through the last event; after the car overheated waiting in line on the grid during practice, we refilled the system and re-bled it. After that, we decided that my friend will always be by the car while I was waiting in line, and he tapped the front bleeder every minute or so until it was time for my next lap. It did work... car didn't overheat for the rest of the event. The strangest thing was every time he would hit the bleeder while I was idling there would be air the first one or two taps, then water. While, every time I would come back from a lap... first tap would always be water. We've been struggling with this issue this whole year... very strange. There is no sign of burning water... not out of the tail pipe or by check the plugs... which is why I'm starting to stay away from the bad coolant seals. The flow issue could definitely be it... tho cavitation is supposed to happen at high rpms... who knows?! :scratch:

Also, when the overheating issue happens at idle... it seems like coolant pressure increases significantly in the radiator/expansion tank, causing the cap to open and dump a lot of water in the overflow reserviour... causing it to overflow in the car lol. I guess I can explain this by assuming that so much air accumulated in one of the lines that it's creating very low water flow though it, causing pressure to build before the blockage and then making the pressure cap open even at lower temps.

My car did the exact same thing and it was teh radiator caps leaking ever so slightly and being too weak for the pressure. replaced them with higher pressure caps and not a problem since.

I have a Griffin 24 PSI cap... so I don't see that being the issue. Also the air accumulates at the top of the engine, and my radiator cap and expansion tank are located in the trunk with the radiator.

Here are some pics of the front setup and the rear (first picture you can see the bleeder valve I keep referencing):
Attachment 663386

I also have an overflow tank attached to the top of the expansion tank now, it's not in the picture tho.
Attachment 663387

Didnt we talk about this a few pages back.

https://www.rx7club.com/build-thread.../#post11297248

As I noted then, you have massively increased the capacity of the system, your stock water pump is probably trying to push 5x the weight of water that it use to. Id be guessing at idle the pump doesn't keep enough pressure up to keep the water moving enough - so is probable just cavitating so there is no water movement.

where at engine speed, the pump speeds up and has enough force to start flowing again.

I know its more money... but if I was you I would have 2 water pumps.one pushing and one pulling. (set off the same controller)

Or one running full speed full time. As I noted before the biggest advantage to a EWP is that its not dictated by engine speed.

Did you block the rear coolant hole on the block ?

Yes I did block the rear coolant hole where the heater core line connected. And yes, I guess I understand what you're saying... I just wasn't sure that cavitation can happen at low rpms. I do want to eventually do a EWP setup, and money is really what's holding me back. I guess for now there is nothing I can do about this issue until the season is over.

Also keep in mind tho, that the engine doesn't overheat as long as air doesn't accumulate enough. So, water must be flowing through the engine... which is why it's hard for me to accept the theory of cavitation at low rpms.

Have you considered varying the engine rpm while bleeding the system? Maybe idle it up to increase flow.

Sweet, sweet body roll

Great Build

The air in the system comes from water boiling in the engine, most likely from insuffisient flow on low idle.

Bingo, you're probably bleeding out almost pure steam, not air. The coolant is locally boiling, most likely right around the spark plug bosses (it can locally be MUCH hotter than what's measured at the coolant neck), since the pump is spinning too slowly to overcome all the additional head losses you've added with the extra tubing lengths and really push around the amount of water you now have in the system.

Centrifugal pumps, like the FC's water pump & turbo compressor, generally have terrible efficiency at low speeds due to the amount of back-flow through the clearances between the rotor & housing. At higher speeds, the pump efficiency improves pretty quickly, explaining why you don't have the problem when drifting. Essentially, you need an EWP, or to avoid idling the car (although you're still over-stressing the stock water pump, potentially causing reliability issues with it). If you're using underdrive pulleys, they're only making the problem much worse.

Yeah, thanks for the advice. My next step will be to either switch to a EWP completely or run one in-line. Haven't decided yet... any opinions?

As the drift season ended, I pulled the engine out and decided to get it ready for winter. I took the turbo/exhaust manifold off and sprayed some Marvel Mystery oil through the exhaust ports, and spun the engine a few times to make sure everything inside is lubricated for the long winter.

Even though the spark plugs were black, and I heard all the 9 puffs strong, water was expelled out of the front rotor when I spun the engine the first time. So I guess the coolant seals went bad or one of the irons has a crack in it after all. This is probably the main reason we kept getting air bubbles in the coolant system. Looks like it's time to save up and get ready for Defined Autoworks to rebuild it :nod:

I am very curious to know the findings, it sure did last a long time not being rebuild. I am somewhat suprised that it made 475 @ 14 on those restrictive exhaust sleeves. What seires motor is it, i didnt see it mentioned anywhere or maybe i missed it. Good luck, keep us posted!

Hoping to put a 20b in my FC! Sick build

I would recomend putting at least one electric pump inline to the rear mounted radiator, other then that, the setup looks solid.

I would like more info on the your dual oil cooler setup though. IE how long of hose you needed and routing, would like to replicate something similar for my road race setup.

Just wanted to say that at the end of the last season I sold my FC. I've had it for 10 years and it's been a great journey, but it's time to move on. I've kept the 20B which will be rebuilt this year by Defined Autoworks. :nod:

I will be building a new 20B powered drift car next year, but it will not be an Rx7.

Here is my last and final drift video, with my progression since 2009. Enjoy!

Unreal last vid. Just coming across this now. What did you end up throwing the built 20B in? if your still on this site lol

Excited to see the end result, keep it up!