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MG MGB Technical - Engine in... radiator blow out...

Ok well had a fun day today on the B. I got the engine back a few days ago, installed it, filled the fluids up and everything. 1950cc's of pure joy, borrowed a friends spare head from his B (He had a early 70's head which is the same as the one my car uses) hooked everything up to give it a quick kick over and it ran perfectly after the normal bit of adjusting the twin HIF-4 carbs. (Got them fully adjusted on the second try! And using a full synthetic 20W-50 oil makes them a hell of a lot faster to respond! :D ) Compression on all cyclinders with my friends head was just about perfect. I ran the beauty for a solid two hours before the radiator went kablewy! Ok I know what your thinking, I didn't keep an eye on the gauge right? Well I did and it never gave any signs of over heating or any such indications anything was wrong. I have replaced the wiring on the car, making sure to use only the correct gauges in it and following a wiring diagram for it. It all works now, but my radiator still failed. I'm guessing one of a few things happened, one being the system over pressurized and blew the radiator apart, two the radiators' age just was too much for it hold out anymore, three a clogged water way backed the flow of coolant up causing it over pressurize, and four the water pump might be putting out a higher pressure then its supposed to? The pumps an aftermarket oem from o'rileys car parts division. Any idea on what happened here, and where I might be able to pick up a good replacement radiator for less then 200US? I'd really like to give my baby her first test drive since she was poorly stored in 2000 by the PO.
I did have the radiator boil cleaned and inspected for any damage just last month at Brit Invasion, nothing was found wrong with it past a little scale build up which was removed when it was cleaned. It was also pressure tested and found to be in excellent shape for its age. It's one of the reasons why I'm so stumped as to why it failed in such a manner. Please give me some idea as to why this might have happened so I can do something to stop it from happening a second time around.

Befuddled CJD
CJD Dark

CJD - What you get for under $200 US is junk that will only give you grief. Take one or both radiators in to a reputable radiator shop and ask for them to recore one of the radiators using a 4 row L type core. These are available from Modine. If they say they can't get such a core or don't know what Modine is, take your radiators some place else that can do it. Modine is a company that makes aftermarket radiator cores to original specs and are world wide and the cores they supply are excellent replacements. I have one in my MGB and the car runs at just under 190 degrees consistantly regardles of speed, load or ambient temperature. The only down side is that it will cost you reight around $300 US to get one installed, but I figure that they would be cheep at twice the price for the peace of mind it gives me.
Good luck - Dave
David DuBois

One problem with getting the radiator recored David is the fact that there's almost nothing left of the radiator to recore. When I said it went kablewy I meant it really went kablewy! It's missing a good chunk of the top now, which is why I'm having to look at getting it replaced because there's nothing left to recore on the older one, its too badly damaged. So any suggstions on a good new radiator that isn't garbage?
CJD

I've never heard of a radiator exploding like that before. There is something seriously wrong here. The kind of pressure that caused what you described means that the system wasn't venting at all and you had to really heat up the water to generate that kind of force. Your cap won't allow it to overpressurize that much...unless you were'nt running a pressure release cap.
Anyway--a cheap radiator will give you the performance you paid for. Kinda like brakes...scrimp here and it costs you lots more money on down the road.
R. L Carleen

Like R.L. For the radiator to explode it was either weak in the first place or you had a non-venting radiator cap. But even with a bad cap it would have to have got very hot in order to build sufficient pressure to do the damage, or there is a head gasket leak allowing compression gases to raise the pressure. I was running a 20lb cap in my V8 for a while because something *was* pressurising the system and eventually something did blow, but it was a hose not the rad.
Paul Hunt

Did you have those Kevlar hoses, BTW? The weakest link may have been the rad if it had a seam that was ready to go.

Going with the description of how the rad went, I vote that it over pressurized probably by a head gasket leak.
Luigi

yup kevlar hoses Luigi, racing style double re-enforcement (not the cheap mixed knock offs); with triton clamps to hold them in place. Just glad it didn't blow on the top hoses side else I'd have a lot more problems right about now. When I get home today I'm gonn strip the head off and see if it was the head gasket creating the problem or a problem with the head itself. But I still need a replacement radiator for the car. Anyone one know of a good reputable radiator company I can get a new radiator through?

CJD
CJD Dark

Do I take it you have had the engine rebuilt?

I hope the synthetic oil is only in the carbs and not in the engine!

Unless you use a straight mineral oil - preferably a unigrade 30 or specific running in oil - then you will glaze the bores.

This will lead to excessive oil consumption (and 1950s are prone to burn oil anyway).
Chris at Octarine Services

Yes the engines rebuilt chris, and the synth oil is only in the carbs, since this was the first time the engines run after the rebuild was complete I looked through the archives for break in procedures for rebuilt engines, lots of good advice inside.

Now since you're around Chris, got any ideas on a good radiator manufactur I could look into?
CJD Dark

Not really, your suppliers seem to be different to ours.

Serck Intertruck may be around in the US - they have a good reputation over here in the UK.

I buy my rads through the MGOC and I have never had any problems - I suspect they buy from Moss Europe, but I guess that Moss USA may have a different source?
Chris at Octarine Services

Proper MG has the UK built radiators on sale now. I'm not sure which one you need, but I know the one that fits a '70 is $199.
J.G. Reed

CJ. You mention that you had the radiator cleaned last month. I would take the radiator back to the people who did the work and ask for their opinion. They should have pressure checked it as part of the cleaning/inspection service.

As to your current problem of not having a radiator that is rebuildable. I would suggest you pick up a used radiator and have it re-cored as David DuBois suggests. My reasons for this are:

I purchased a new, Made in England radiator for my GT about five years ago. It lasted four years and the seam between the hearder tank and the core seperated and it began to leak. I replaced it with the original radiator, some 30+ years old, which is working fine. Thus, the new radiators do not seem to be made to the same quality as the original ones, nor is the quality of the metal as good. Yes, my pressure cap is working. I have a Stant cooling system pressure checker and check both the cooling system and caps periodically to see that they are in good condition.

With the factory style radiator, my stock engine runs hot, sometimes very hot, in summer. The people who have had the Modine recore done report that they are running much cooler than my stock system. Hence, this will be one of my spring projects. I want to see exactly how much cooler it is running and how it will handle the cooling in stop and go traffic. This would be especially important with an engine built up to greater than stock size and performance.

I would suggest using stock hoses until you find the cause of the problem. If the pressure cap was venting properly, it should have been able to handle the pressure. To me, I would rather replace hoses every year than have a radiator explode. One of the things never discussed about the use of kevlar hoses is that the rubber hoses are intended to be the weak link in the system and, if one is going to upgrade their strength, the radiator should also be upgraded to one of stronger construction. Les
Les Bengtson

Ah but Les finding a good used radiator where I'm at is well nearly impossible to do. The only MG club that was here that could've been of some help to me disbanded over two years ago from what I've been able to find out, so going through them and checking for a used one is not an option. Junk yards here Crush these cars because nobody wants them at all, which is really sad considering some of them had crap loads of parts I could've pirated for my own B project. Like a rebuildable cyclinder head for one, can't use my buddys' forever; or a radiator. Those few precious cars that aren't crushed are so far gone that there unrecoverable. If you wanna know how little an MG is treated and respected here, drive along hwy 6 in houston and you'll see an MG mgb roadster with a sign post running straight through the cockpit.

(Another small question... uh Where can I find a rebuildable Cyclinder head thats not cracked length wise like my poor one is. *PO over torqued the studs we think and cracked it.*)

Thanks! CJD
CJD Dark

CJ. E-mail Bob Schaulin at gbmg@aol.com and mention my name. Bob, and his brother Gil, operate a quite extensive MG "resting yard". I have bought a ton of spare parts from them over the years, including cylinder heads. They will also have the radiator you need.

As to other options for cylinder heads, Peter Burgess and Chris Betson might be possible sources, but I would check with Bob first. Which ever source you decide to use, make it a requirement that they have the cylinder heads crack inspected before sending it to you. Over 80% of the RB cylinder heads I see are cracked. About 50% of the CB heads seem to be cracked. Makes things more difficult, especially if you find out after you have bought one and taken it to the machine shop. Check out the article on my website, "Crack Inspection for the Hobbyist" to see one form of crack testing. The magnetic forms are even better, being able to detect a crack that is forming (sometimes) before it reaches the surface. Website is www.custompistols.com/ and you want the MG section. Les
Les Bengtson

I lucked out today, and found a 73MGB-GT that was being parted out after being in a wreck. Got a freshly rebuilt radiator(Modine recore), and cylinder head with receipts and warrenty for 100 bucks. :D Finally getting some luck!

Hey uh would anyone happen to have a wiring diagram for a 72 MGB on their computer they could e-mail to me? I need to track down a gremlin and the auto electrician (He only does european cars, and is familiar with the MG's) I had do the work on the Vixen just moved so I'm kinda stuck.

I'm also moving the OD switch from the shifter knob to the radio console because the switch doesn't work. OD Works fine, but the little peice of metal in the switch rusted off.

Took the blown radiator in to the shop to have them look at it, they figured out what happened in less then a minute. The cap failed to work (Duh), and the over flow pipe under the cap seems to be clogged up with a chunk of brazing. Left no where for the pressure to go so it went Boom! They asked for my water pump manufacter to, it seems they've had some problems with certain pump makers. GMP being one of them, good flow rate but flows at a higher pressure then its supposed to. 72MGB water pump is supposed to be at 10psi, pump from GMP is at 15psi.
CJD Dark

CDJ; There is a wiring diagram for 71 & 72 MGB's at:
http://www.mgbexperience.com/view/index.php?service/wiring-7172.jpg
Clifton
Clifton Gordon

CJD,

If you would still like to keep the OD switch on the shifter, the switch can be easily replaced.

The replacement part is Moss#141-320. It is listed on page 86 of the new catalog, but they don't show a picture of it.
sliedavs

CJ, I think your radiator shop is giving you a little bit of "Baffle them with Bull Sh*t". The water pump should be no issue with regard to building pressure in the system unless it is allowing overheating due to not flowing enough. Also, did they do a pressure test on the cap? A 15 psi cap would require a temp of about 260F to vent. If you had a good running motor for 2 hours, you should not have overheated.
Edd Weninger

Ditto on the BS. The cooling system is a closed loop. Pressure should not build up from the pump if the thermostat is open. If it's closed, the pressure would build in the block. Only overheating should cause a pressure build up. Expansion, remeber. I suspect a bad head seal, allowing pressure to build in the cooling system. A bad cap could cause pressure to build (or the wrong type cap). The bit of brazing clogging the overflow sounds suspicious as well, if the radiator had tested OK previously.
R. L Carleen

Hope I didnt catch you too late

If there is any coolant left save some
and have it tested for exhaust gas prior to
rippin the head off....
HowY

CJD. You said boild and presure checked. Did they flow check it or rod the core? Also what did you use for a radiator cap? Long befor your tank blew the cap should have vented. Take the old cap and have it checked. A properly running not overheated engine will blow any radiator with a bad cap. The water pump will flow more but only if the radiator is clear and will feed the water. The pressure differential between the engine, block and pump is not so great as to cause your problem. I use only a 7lb cap on my B with no problem. Perhaps with a new radiator I would go back to a 12 but nothing stronger.

On the other hnad. If you are running 1950cc and have other modifications...go to a speed shop and fit a racing radiator infront of your power plant.

cheers. doug
Doug Gordon

This thread was discussed between 04/03/2004 and 09/03/2004

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