MGB & GT Forum

A week or so ago I posted on installing a radiator drain petcock on my 1973 roadster. Many offered superb suggestions and encouragement for this.

As I have mentioned I read the many archived pages (now up to 490!). There are many, many gems there.

There I discovered the existence of a fluid block drain, just behind the distributor on the RH side. Threaded and ready for a petcock - which was on the early MGBs!

The discussion was on cleaning out the drain after engine overhaul. But one of those "gems" noted the utility of using this drain port.

Yes, I can braze in a petcock to the radiator, but using this existing drain site may have a lot of merit - easier, faster, cheaper.

One downside is the tight area there, but it remains an interesting idea.

As always, the collective guidance of the site is appreciated.

Steve


Steve Hull
Arcadia, OK
1973 roadster

405 550 3023

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Steve

truth: that which is boldly stated and firmly maintained . . . . .

Steve Hull
Arcadia, OK
73 MGB

405 550 3023

Hi Steve, when I removed that plug I was expecting anti-freeze to go everywhere - to my surprise nothing came out. Others here say that area of the engine usually clogs up but does not hurt the cooling of the engine.

Steve,
This drain petcock is designed for exactly as you write, to drain the cylinder block. It is installed at the lowest part of the water jacket in the cylinder block. So for draining the block it is perfect.
However as you have read, this rearmost coolant passage is often owner neglected, (infrequent block flushing etc.) and this passageway gets clogged with corrosion. If you have your engine apart this is a good time to clean this, both vertically and laterally.

This petcock is quite a bit higher than the lowest point of the radiator so if your goal is to drain the coolant completely in the radiator, then the only choice is a drain in the bottom tank of the radiator.
A great many of us simply remove the lower radiator hose and catch the coolant in a tray.

If your cylinder block has been maintained then this petcock is useful, caveat; coolant recovery is difficult, distributor protection vital and access a bugger.

B

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Life's most persistent and urgent question is, "What are you doing for others?"

Is that location low enough to drain the whole system?

Edit: I thought not. That's why I never bothered it it and installed rad drains instead



Edited 1 time(s). Last edit at 2017-12-14 08:01 AM by Gerry.

To clear the blocked line, I have a thin length of BRASS welding/brazing rod (uncoated). It's thin enough to go around the internal bends and because it's brass it's soft enough to not scratch the block. I've use this with success on both my cars.

~ Carl

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1972 MGB roadster - 30 over, fast road cam, full peco exhaust, Jeff S. rebuilt 45D Eurospec, Jimmy H. rebuilt HIF4s prestige interior, hood and tonneau cover, Dayton 72 spoke chrome wires, custom center console

1969 MGB GT - Eaton M-45 supercharger, TT stainless exhaust, Jeff S re-curved 25D - SOLD

It is a very small opening that turns upward in the block. Many people have attempted to clear the passage (including me) with little/no success.

My experience has been that this horizontal passage is 5/16" ? diameter. Once the petcock or plug is removed if one finds this solidly plugged with corrosion, then a use of sequential size drill bits, held in a tap handle and turned by hand will quickly remove the 'silt'. The vertical passage cleaning is a tad more complicated as the cylinder head needs to be removed. Then from the rear most coolant passages, (at the block deck) a long drill bit can be used in the same fashion. Once this is loosened up the 'dust' will fall out the lower hole, aided by a little air pressure. I have successfully cleaned 3 cylinder blocks this way.

A while back Gerry offered some advice that I followed. He suggests using vinegar so I dumped some cleaning vinegar in the block, let it pickle for a while then drained/flushed the block.

More importantly, this 'blocked' drain is only a symptom. What this indicates is the rear coolant jacket of the engine is partially bunged up and may/will attribute to insufficient cooling of the engine at the rear cylinders, and maybe the cylinder head.

B

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Life's most persistent and urgent question is, "What are you doing for others?"

Once again, the wisdom on the group is impressive! Out comes the radiator for a petcock installed there.

You guys are the BEST!!


Steve


Steve Hull
Arcadia, OK
1973 roadster
405 550 3023

---

Steve

truth: that which is boldly stated and firmly maintained . . . . .

Steve Hull
Arcadia, OK
73 MGB

405 550 3023

Does the picture show the drain opened or closed?To me it shows it open.

Bob, the manual shows that position to confirm that no matter where the handle is turned, nothing will come out....

good one Wray.

Bob,
The picture shows the petcock in the closed position. Contrary to what we are familiar with, think ball valve etc. but such as it is.

I should think that your 1966 MGB is fitted with this petcock, no?

B

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Life's most persistent and urgent question is, "What are you doing for others?"

Good one .Glad I didn't try close or open it.