Good day. On my 1968 400, I changed to an aluminum radiator after a flush of clean antifreeze, installed new coolant and tank, alternator, belts, fan, fan clutch, and thermostat. All seemed fine. Now I have a slow leak right underneath the thermostat outlet. Not coming from the thermostat or gasket. I’m thinking it’s leaking from the timing chain cover.

this all being said, has anyone changed from the 8 bolt H2O pump to the 11 bolt? I understand that cooling is a lot better with the newer improved 11 bolt that premiered in 1969. I live in Florida may do a lot of idling at Crusin the Coast 2026. Thanks for any help.

Edited January 22Jan 22 by TKYachts
Misspelling and OCD.

Hi TKYachts. Welcome to FP and the madness.

Yes the 8-to-11 bolt is an effective upgrade to your 400. It's justa not a cheap one! Butler Performance has a complete kit, but you essentially need a whole new cover, water pump, divider plates, bolts, gaskets and engine pulleys to support the change. So this runs around $800 from Butler or you can piecemeal it. Still it's not cheap. However, your engine may thank you with a more modern water pump. The alternative is to try to fix your existing leak with new gaskets, sealant, bolts, etc.

I did Cruisin the Coast back in 2004 in my Lemans convertible with my stock radiator (4 core), factory flex fan, 180-degree WIde Mouth Mr Gasket thermostat and 11-bolt cover (stock for my '72 455). It handles parade duty and the Woodward Dream Cruise (a.k.a. Dream Crawl really) just fine.

https://butlerperformance.com/i-31643308-butler-performance1964-19678-bolt-to-11-bolt-timing-cover-conversion-kit-non-ac.html?srsltid=AfmBOoo_MXokV-3ylS0FNbTyTTjPx7iyCUyQl0Bnsea2kEffKBXsMyPZ

Thank you for the information. I would hate to replace gaskets, etc and then think back going “darn I wish I had installed the 11 bolt”. I’ve checked into the kit (actually prior to the post). It’s about $954 landed. Now, what’s the general consensus on choice of impellers? Billet? What one do you think moves the most water? BTW if those parts were for a boat or RV they would be $3k!

Edited January 25Jan 25 by TKYachts

I prefer the cast impellers as they can be "spaced" to move more fluid, so remember to check the spacing of the backing plate to the impeller, and I would go with new transfer tubes and seals. and remember when installing the front cover to loosen the intake manifold bolts, and use the small long bolt to gently pull the intake forward to seal properly, then retorque the intake manifold.

Good luck!

Cammerjeff,

Thank you for the tips. Followed your advice on the impeller. Figured I’d replace the fuel pump while I was at it with everything else torn apart. Waiting on parts. Wish me luck!

I installed a decent slightly oversized radiator with larger tubes and er, other things...too long ago to remember everything now. Anyway, I also installed a Flowkooler waterwheel type pump. I live in a hot place and the engine temp never strays from 180°.

Getting that last bolt to tighten the pump to inlet manifold crossover is a pain. I was very careful with mine and have the tiniest coolant weep - just a stain really, but enough to annoy me whenever I look at it.

Why the conversion kit costs so much is beyond me - I didn't bother having already spent countless thousands on everything else.