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MG MGB GT V8 Factory Originals Technical - Coolant leaks from back of block

Last job to do before an attempt at starting my Rover 3.5 was to add the coolant.

Just about had the rad full when the sound of coolant dripping on the garage floor was heard. I thought it would be something simple like the heater valve but no joy.

I pressure-checked the system and about 7 lbs caused a fairly good stream to appear at the bell-housing.

I talked to my local Rover specialist and she couldn't think of anything back there that would leak except the core plugs. I had the engine re-built some time ago but am pretty sure the plugs were in there (I like to think I'd see something like that missing or improperly fitted).

Thought I'd run this by you guys to see if there's anything else possible before I pull the motor.

I managed to look up inside the bell-housing by un-bolting the panel that sits between the engine and lower part of the housing and can see droplets of coolant in there (my fears confirmed, I believe!)

Any thoughts?

Thanks
Simon

Simon Austin

Simon - you sound pretty familiar with the kit and probably are right but there are several possibilities such as the pipe which runs (in a factory MGBGTV8)through the valley and under the manifolding or the rubber hose between that steel pipe and the heater or the inlet manifold itself which transfers water at the rear (have you fitted the right gasket for your engine and is the alumimium manifold corroded there ?).

I hope the water is coming out of the heater return line - for your sake !

Roger
RMW

Simon,
I can share my experience with coolant leaks on my Olds 3.5 engine conversion and assume that the Rover might have similar issues.
Any leak at the thermostat housing/bypass hose area or heater return hose to pump at the front of the engine will trickle down the valley cover and make it's presence known at and under the bellhousing.
The other leakage issue that I've had is a leak from a couple of the exhaust manifold bolts which thread into water galleries and require sealant on the threads - again, the tendency is to have the coolant run towards the rear of the engine and show up at the bellhousing area (albeit to the left or right of centre).
Graham
Graham Creswick

Thanks for the tips, guys. I checked as much of the tray under the manifold that I could see and the only place it showed coolant was under the sensor for the temp gauge. The rest of the tray was bone-dry.

I had a good look all around the bell-housing and can't see anywhere that would indicate a leak from on top of the engine.

The first leak that developed before pressure was even introduced was at the oil-pan bolt that runs along the back of the pan on the driver's side. There is a bar between this bolt and it's mate on the passenger side. After I pumped up the pressure, there was a very steady stream coming from the passenger side at the rear of the oil-pan/bell-housing.

Roger- I ran that particular hose not under the manifold but along the valve cover. I wish it was as simple as one of these lines but even with pressure in the system, these connections seem good. I modified an MGB heater valve using the original Rover plate over the rear outlet and again, it seems to have a good seal. The gasket appeared to be correct and the manifold is brand-new so corrosion isn't an issue.

Graham- I'll check out these bolts you mention just to eliminate that aspect. Would these bolts happen to be the last one or two on each side? Seems so long ago my biggest problem was finding an air cleaner!!

I guess the fact that the leaks appear to be coming from the rear of the block, at the oil-pan where it meets that panel and not so much at the actual bottom of the bell-housing is what has me worried and planning an engine pull over the next few days.

Thanks again!
Simon

Simon Austin

Sounds as 'tho your original diagnosis was right - I hate pulling these engines.

Roger
RMW

Simon,
All exhaust manifold bolts require sealant (at least for the BOP engines) as they thread into wet galleries. Try removing a couple of bolts for visual evidence of coolant coming out of the hole. Because of the engine power angle, exhaust manifold coolant leaks tend to migrate towards the rear of the block.
Graham Creswick

Now a new day has dawned, I can tackle this project with renewed enthusiasm.

Any particular sealant you'd recommend on those bolts, Graham? Since I'll be removing the manifolds anyway, might as well put them back on correctly.

I'll let you guys know how it goes.

Cheers
Simon
Simon Austin

Simon,
I believe I used red Permatex RTV silicone (the same sealant I used on all the head bolts), but I think the Grey RTV is formulated for exhaust manifold bolts. Check out the Permatex website or visit your friendly local Canadian Tire Store.
Graham Creswick

Graham - for the record only - I do not believe the MG (LandRover 3.5 137 BHP or Rover 3.9 190BHP)heads were drilled for the exhaust manifolds as far as the coolant chamber but the inlet manifolds may be a different kettle of fish - here the bolts at either end may possibly go into the water channels and indeed Buick versions may, and probably do, vary.

Simon - some of us are holding our breath.

Roger

RMW

Gents,

Further to the story; I spoke to the guy who rebuilt my engine and he never changed the core plugs. Apparently he felt they looked okay and didn't need it. The other Rover he was doing at the time had it's plugs replaces due to severe corrosion.

My Rover specialist showed me another block with new plugs and said even old ones can look that good but be rusted on the inside. Lesson inserted here: CHANGE THE PLUGS AT EVERY REBUILD!!!

Graham- I asked my specialist about the sealant and she said she's never used it. I've removed the parts under the hood I need to to get the engine out and when the exhaust bolts came out, they had no coolant on any of them.

Hopefully get the engine out tomorrow and will update then.

Cheers
Simon
Simon Austin

Further update to the story:

Got the engine out and it would appear the plug on the left is at fault. I haven't removed them yet but just looking at the two of them, the left one sits further into the block than it's mate. Don't know if this is the problem yet or not. There is (was) sealant used around them as well but because of the position of the left one, it doesn't appear to be doing anything.

I'll update when I get them out.

Cheers
Simon
Simon Austin

Final chapter in this story;

Off-kilter core plug was changed as well as two others that decided to leak after system pressure was built up. Looking at the plugs, it was pretty obvious they had been changed so I only swapped out the ones that needed it.

The one on the left bank at the rear caused some grief in that it refused to seal properly even after liberal applications of sealant. The "casting seam" of the block runs right through the opening and it appeared there was a slight flaw in the opening that was allowing coolant to trickle out under pressure. Some dressing with emery cloth to smooth out the flaws and a friend gave me his Loctite sealant to try which seems to work very well.

Engine went back in last night and hopefully get it back together shortly and attempt a first start this weekend.

Thanks again for the help!

Cheers
Simon
Simon Austin

Simon

I have followed this thread with great interest as I have had similar problems.

I do all my own work but when it comes to changing welch plugs I am always 'nervous'!

My engine has a similar flaw near the casting seam.

I hope it is all good news from now on.

cheers
Ian Buckley

To add a comment:
I always use brass replacments for the core plugs. A small extra cost but long term insurance. A core plug kit for a Ford 351 will fit most of the holes for a 3.5

Kelly
Kelly Combes

Funny you should mention the brass plugs, Kelly. I did a search in the archives under "core plugs" and one of the threads included brass plugs.

Bit of a mixed debate on whether they should/could be used. Interesting read though.

Cheers
Simon
Simon Austin

This thread was discussed between 07/10/2004 and 24/10/2004

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