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How to make yer own coolant expansion tank


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With the weather being pretty hot right now, close to 100 every day, I thought my 521 might need an expansion tank next to the radiator. I don't have any problems overheating but, this idea cannot hurt anything. To have the coolant go into a tank instead of on the ground is better in my opinion.


Very few items are needed for this little project...

A drill

A few zip ties




3/8" tubing



I used a 1.75 liter jug. Anything larger may not fit in the space next to the 521 rad.



Next thing I did was drill a hole in the jug lid, slightly smaller than the tubing



On the end of tubing that is going into the jug I cut an angle piece out just to be sure it sucks out coolant.



I inserted tube into jug on one end and the small pipe under rad cap on other end. I did not use the small clamp, used a zip tie instead.



Secured tank with one tie at the top and I may put one on the bottom but, it fits pretty snug in there so we will see what happens.








Total time for install was meybe 15 minutes. After install I drove it around for 20 minutes and it seems pretty secure. Total cost including the lemonade jug was $6. :)

I decided to leave the labels on the jug, my Datto likes lemonade.:D

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Unless you have the proper rad cap you will have to manually empty the catch can into the rad when it cools. The proper rad cap allows the liquid to siphon back into the rad as it cools and contracts. Starting with the '78 620, coolant recovery was used, so a '78 cap should fit the bill for your rad. Cap # 21430 C0500


Still it's a great idea to prevent waste. I did this on my 521 back in the day.

Edited by datzenmike
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Phiz, I heard about that energy drink a while back but never have seen it on the shelves around here.


On the coolant bottle, I went a little different route with mine. I found one from a 91 honda accord, took the bracket too. It is mounted in factory holes to the core support, by drilling two new holes in the bottle bracket and using a couple of washers as spacers to keep from smashing the rib/bump in the back of the honda bracket. Bumps can be seen in the second pic.

Couple of pics...





I was more interested in an appearance that looked factory for mine.:cool:

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Guest DatsuNoob

I bought one of those "Venom" energy drinks the other day, and was surprised at how sturdy the aluminum bottle was for being a disposable. They're very thick. I may make one out of it.

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I bought a home made one of of ebay, painted it and put it on the front bumper! But if I were going to run a bottle or can, dude, it has to be a Japanese soda or beer!!!


Get creative people!














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haha good form....


mine's made from a Sauza tequila bottle! only some tequila left...:P





You know liquor is the home treatment for antifreeze ingestion? lol Just fyi.



Cudos to fisch too, I agree and thats my plan. To get my girls fam to send me some crazy shit no one here will have seen let alone have.

Edited by 72240z
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  • 9 months later...

a word of caution i made one out of the nos energy drink bottle as shown earlier in the thread and the hot coolant caused it to contract and spit all my coolant out of the radiator on the way to Monteray i then promptly replaced it with a zx bottle so if your going to make one out like in this thread i advise glass or an aluminum can

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