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MG MGB Technical - Cooked engine help please.
| Well, this is a bit of a story but basically my engine is severely overheating and losing coolant. Is a long story but I know you guys like all the facts! Saturday I went off to a race meeting (Roycroft trophy) which is a race event here for pre 1960 cars organised by the vintage car club. Great weekend and of interest to me since I am building a little Austin 7 myself. Anyway, it's about 70km away, all motorway driving. I set off and half way there pulled into a service station since my engine was running hot, up near 120C (the gauge pegs at about 125C). I opened the bonnet and found a tiny leak on the top tank of the radiator where the metal pipe the hose attached to is. I should add mine is a 78 B with the overflow tank having the pressure cap and no cap in the radiator itself. I bought some stop leak and put it in the overflow and limped to the track. As I arrive the gauge was pegged. The engine was hot and my idle oil pressure was low I guess doe to hot oil. Had a great day watching the vintage racing and chatting to people and looking at cars. Someone insisted on a lift back with me so we set off. I topped up the overflow tank before we left. Didn't get more than a few KM before the gauge pegged and there was steam coming from the cap. We pulled over just as the engine was starting to feel a bit rough. Seems I hadn't tightened it fully. Feeling the hoses the top hose was boiling hot and the lower hose totally cool. We let it all cool and pulled the thermostat housing. The stat was wide open so seems to be working fine. But there was no water in the block at all. We let it cool then filled it up. Is hard to get all the air out of the system. Especially parked on a hill! Anyway, we limped home and got there just as the gauge pegged again. My lift person insisted on a lift back down for the next days racing. I wasn't so keen. Even if I fixed the leak I didn't want the first test drive to be another 70km motorway slog. I suggested taking his car but he said his wife MIGHT need it the next day. So I finally got home, soldered up the leak and refilled it all with water and made sure the thermostat housing was all sealed up properly. Next morning we got down there and again just as we arrived the gauge was right near the top. There was a parade at lunchtime of all the MGs there (the club was there for the 50th anniversary of Bs) so I did that and again pegged the gauge at the end of it. I re-topped up the water in the overflow tank. I suspect this is part of the issue. If you have air in the rest of the system does filling this actually do anything? I also turned back the advance a little with the vernier in case that was the issue. I ditched my passenger and left early alone and had major overheating all the way home. I had to stop 5 times! On the last stop, a few km from home, I let it totally cool and had a look in the thermostat housing and again no water! I had to put several litres back in once it all cooled down. I finally made it the last few km home with the gauge on 100. So, it seems I am losing water somewhere. I wonder if the pin hole originally due to initial overheating was a cause of an effect of all this. I checked the dip stick and the oil looks clean. Also the oil on the rockers looks nice and clean too (having earlier in the week replaced the rocker cover gasket). There are no obvious leaks in the pipes or radiator or tank. The only thing I can think of is it is burning it and I am losing it as steam in the exhaust or as I drive the system is being pressurised and shooting it out of the overflow and leaving me with air in top of the engine/radiator. What do I do next? Seems I should take the head off to check the head gasket? Can I do a compression test to see if that tells me anything? Also will looking in through the thermostat housing for bubbles in the coolant work. Unfortunately with this system you can't look in the top tank of the radiator since the filler cap is on the overflow tank. Also what damage is likely to have been done to the engine running so hot? When it isn't overheat is still seems to run fine. Any advice would be most welcome! In the last few weeks I have had a rear wheel oil seal go, the starter solenoid fail and the rocker cover gasket leak. I think she's jealous of all the time spent on my little Austin! Simon |
| Simon Jansen |
| Hi Simon, What a sad story! Hopefully there is minimal co-lateral damage. What could have happened is a blown head gasket, cracked and or warped head, piston rings losing their springyness,if the oil pressure was down whilst running then damaged bearings. With a bit of luck none of these will have happened. I would ditch that radiator and replace it with one with a filler, and use a recovery cap. Best of luck Herb |
| Herb Adler |
| Simon. Put a radiator pressure test device onto the filler neck of the overflow tank, then pump up the pressure to the rated pressure of your pressure cap. If you are losing pressure, the gauge on the device will tell you. You can also use said device for pressure testing the cap to see if it is operating at its rated pressure or letting loose early. No, the system cannot be filled simply by putting water into the expansion (overflow) tank. It simply catches the overflow from the hot radiator and sucks it back into the radiator/engine system as the system cools. Basic filling/refilling is done through the plug on top of the thermostat housing which, from the factory, was made of plastic and tended to crack in use. Think I went through three of them (original plus two factory replacements) in about six years of ownership on a new 79B. On later cars, I found a brass plug which does not deteriorate in use. Running the engine that hot, several times, greatly increases the chance of cracking the cylinder head or compromising the head gasket. A compression check should give you some idea of the condition of the head gasket. But, I would pull the cylinder head, inspect, then replace, the head gasket, check the head for straightness and, if at all possible, have it crack inspected. Les |
| Les Bengtson |
| Hi Les, funny timing. I was just discussing with a friend doing a pressure test first. Somebody else also suggested doing that. I have a small manifold I use for testing model steam engine boilers I can use possibly by hooking it onto the hose between the tank and the radiator. I have been told not to go above 15 psi. I have a 13 psi cap so that should be fine. I also have a brass plug for the thermostat housing. I have found in the past even filling from there it is tricky to get all the air out. Oil pressure was good when running. Still 50-60 PSI. Low pressure was about 10. Will pull the head and check it as suggested too. Simon |
| Simon Jansen |
| I did a compression test when I got home tonight. Cylinders dry, WOT. I then left each for 5 minutes to see what they went down to. The numbers below show the cylinder, the initial pressure then pressure after 5 minutes. 1: 170 167 2: 165 162 3: 170 167 4: 170 170 I guess that seems OK? Next is to try pressurising the cooling system to see if it holds. I am making up a little manifold thing with a gauge and a valve on it so I can use a tyre pump to carefully bring it up. Will have to do the expansion tank separate from the radiator/engine since I only have enough random hose fittings to do it that way. |
| Simon Jansen |
| I find removing the hose from the thermostat and filling it through the hose untill water runs out of the thermostat is easier. I have a brass plug, and they can corrode. I cracked the housing undoing it once. |
| c cummins |
| Simon, with figures like these no way should you pull the head as you stand a good chance of not getting it sealing so well again. What about the rad, is it in good condition and free flowing or is it due to be replaced are the fins corroded and inefficient and what about the water pump. Try these before taking any drastic action |
| Iain MacKintosh |
| Simon Just a suggestion If the engine was that hot and the top hose was hot but the bottom hose cold , it suggests that your radiator is probably blocked Really, if it is that hot and the thermostat is open or removed it would be hot everywhere It might not be your problem but it sounds a bit that way to me Another test you can do to check if the headgasket is giving trouble is to remove the pressure cap and find a funnel that fits tight in the hole and half fill the funnel with water--start the engine and let it run for a while giving it a few revs every now and then If the headgasket or the head are giving trouble there will be a trail of bubbles coming up into the funnel Cheers Willy |
| William Revit |
| The first thing to be aware of is that topping up the expansion tank does *not* refill the cooling system. You *must* remove the plug on the thermostat housing and fill the system from there, then top up the expansion tank. Checking and topping-up the tank is fine as a weekly check when there has been no work done on the system or no loss of coolant, but for the scenario you describe you probably lost several pints. As the engine cooled it would have sucked what was in the expansion tank into the engine (half a pint?), but any you subsequently added to the expansion tank would just have sat there and never got into the engine, ditto for the stop-leak. Refill the system from the plug on the thermostat housing, top-up the expansion tank, and start from there. Park the car slightly nose-up and it should burp itself, this will be seen as a stream of bubbles in the expansion tank as the engine heats up, don't panic at this stage. It may take a couple of heat/cool cycles to fully burp itself. After that, if you still see bubbles in the expansion tank, and it still goes up the gauge, then you have done some damage. Unfortunately the temperature gauge is a pretty useless indication of coolant loss, only when the coolant loss is so prolonged and severe it does start to damage the engine. |
| PaulH Solihull |
| Won't pull the head just yet then! When cool the engine does run fine. I didn't notice any power loss or things like that. Will do the pressure test tonight. I should add everything on the car is effectively new since the last rebuild and I have done less than 600km so far. The radiator was flushed and tested by a radiator company, new water pump was fitted, new radiator cap, all new hoses, thermostat cover, brass plug, etc. Could the pump have failed somehow? I will drain and flush the whole system too. Will fill from the brass plug from now on! Is there a special spanner of those things as they seem a bugger to remove. Thanks for the help so far. Will get to the bottom of it eventually! |
| Simon Jansen |
| Simon, A lot of good info from all and given the amount of new or refurbished parts, my response to.... "Feeling the hoses the top hose was boiling hot and the lower hose totally cool" suggests a pump failure. Depending on the quality of the pump fitted it is not unknown for the impeller to come adrift from the shaft. Or at least spin on the shaft rather than with it. This is usually accompanied by an increase in noise from the front of the engine but if the impeller is made of plastic, perhaps not.. Pull the pump to check. MGmike |
| M McAndrew |
| Right, some more debugging. I pressure tested the expansion tank first. That was fine. The 13 PSI cap works and the pressure stabilised at 12PSI on my test gauge (not sure how accurate the gauge is but good enough!). I also pressure tested the radiator/engine. This was interesting. I found one small leak around the hose clip on the top hose if it was moved a certain way. Tightening that fixed it. I suspect it was fine before and me removing the thermostat housing disturbed it. I also found another leak on my heater valve. I have a quarter turn ball valve. The body of that had unscrewed a little and with the valve open there was a definite leak. With it closed the rad/engine held pressure fine for the 20 minutes or so I waited to see. Leaking it was slowly losing pressure. I fixed that. I then topped everything up and ran it at fast idle for a while with the brass plug out. No bubbles at all. I put the plug back in and let it heat up to about 80 C (middle of my gauge) at which point my radiator fan came on. I stopped then and had a look at things. No obvious leaks anywhere (bit tricky to tell though as there is water all over the show at the moment due to my doings). The top hose was hot. So is the top of the radiator. Too hot to hold your hand on. The bottom hose was cold as is the bottom of the radiator. So, as MGMike suggests, maybe the water pump? Can't hurt to pull it to take a look. I listened carefully at the front of the engine and every so often there was an odd little noise. Maybe the impeller is spinning on the shaft? Then it got too dark to see so that will be tomorrows job. |
| Simon Jansen |
| If the top of the rad is hot and the bottom cold whilst it could be the pump it looks more likely to me that the thermostat is not operating correctly. |
| Iain MacKintosh |
| Simon Interesting - it could well be a pump problem Laugh at this if you want to Would there be any chance that the polarity of your electric cooling fan is about face, any recent work in that area-------- If it is around the wrong way it will be blowing air outwards from the front of the car, the result being that it will be fine at standstill but as soon as you get moving the radiator gets caught in an airlock at some speeds and gives the same result as you have there |
| William Revit |
| A thermostat fully stuck closed should prevent the top hose getting hot, certainly the top of the radiator. When warming from cold the top hose and top of the rad should suddenly get very hot as the thermostat opens. If the top of the rad gradually warms from cold the thermostat is stuck open. And if it is stuck *partially* i.e. only slightly open then even with the pump working normally it won't circulate the coolant through the rad fast enough to get the whole thing warm, but the fan will eventually cut in. If the top of the rad does suddenly get very hot as the temp gauge gets towards N, then it looks like the stat is OK. As far as pumps go I don't know the details but I have heard on more than one occasion that there are two pumps for MGB engines, they are interchangeable in one direction at least, and one of the incorrect combinations at least gives very poor circulation. William's fan rotation is no laughing matter, that definitely will cause lack of cooling when under way. But in that case the bottom of the rad would be as hot as the top assuming the coolant is circulating as it should. |
| PaulH Solihull |
| William, I won't laugh at that since although my radiator fan is going the right way (I did check) I did have the heater fan blowing the wrong way for about a year and always wondered why the heater was no good! Iain, the thermostat is working OK. We pulled the housing when things were still fairly hot and the thermostat was wide open. I was able to see it close slowly as it cooled down. When I first built the car I am ashamed to say I had the thermostat upside down (it seemed to make sense to me you should be able to read the temp written on the base when you open the plug) but it is definitely up the right way now. Seems to me if the pump isn't working all the heat will be at the top which is what I am seeing. Will pull it tomorrow and let you all know! Simon |
| Simon Jansen |
OK, home again and water pump pulled. The impeller is fine. I was stumped for a bit until I looked down the outlet pipe. It's blocked! There is a layer of stuff there. At first I thought it was crud or else the stop leak I put in there (although that went in the reservoir so none probably made it to the block). But it is hard and I think it's part of the original casting. A few firm jabs with a screwdriver didn't break it. It must have always been that way (the car has always run warm). Is this normal? I am guessing not. There are a few holes in it so some water does get through but certainly not in a hurry. If it's not meant to be there I can probably chisel or drill it out but I wanted to check here first.
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| Simon Jansen |
| Not sure about the pump you have but many years ago I bought one for a Holden Torana and was required to drill the 'specified' application model diameter hole in that region of the pump. Like your description, my pump had a cast seal across the diameter of that throat. Your pump may be a similar 'multi-application' type. Not sure though how your pump has managed to pass any coolant if it is a solid plug requiring drilling. Is there perhaps a small drilling there already? If that is so I would wonder whether things like impellar depth on your pump were ideal for a B? perhaps a B correct pump for peace of mind? |
| Roger T |
| It is a proper B pump. Was a new replacement a few years ago when I built the engine. There are some holes there. It's not very thick so some water is getting through. |
| Simon Jansen |
| Well, a B application perhaps, but not quite 'proper' for that application. Still wonder whether I'd drill it out or replace - ensuring a flowing throat on the latter of course. If you drill be careful to extract ALL drill shavings. |
| Roger T |
| The kind of thing nightmares are made of! It's a casting defect caused by the core breaking before or as it was cast, so there is a diaphragm across the port. Probably quite thin, so you can knock it out with a punch and hammer. Never should have gotten out of the foundry - it's their job to check for such and fix it, nor past machining. I've seen similar inside cylinder heads, but this is so easy to see before the pump is assembled. FRM |
| FR Millmore |
| Given what FRM said I went and knocked it out. I used a socket extension about the right diameter and it came out in two pieces. I blew the housing clean with air in case there were other bits lurking in there. This is what it was. Definitely left over from casting. Funny thing is it's always been that way and the car has done 5000 km now! It always seemed to be a little hotter than it should have been but didn't usually max out the gauge. There must have been just enough flowing through to prevent overheating in usual conditions. Now tomorrows job is to reassemble it all again. Was the first engine I ever assembled and it never occurred to me to look down the throat of a brand new pump. 
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| Simon Jansen |
| Yes, it does appear that there were some small apertures through the 'plate'. Do a manual spin of the impellar to listen and make sure there are no bitsy sounds inside. Don't feel too bad about not looking down the throat prior to installing it. I didn't either with the Torana pump. I did manage to read the box though prior to running it and I was not impressed - a second complete job required to be able to do the required drilling! I tend to look parts over now prior to installing. All part of the experience I suppose. You should be good to go from here. Good luck. Regards Roger |
| Roger T |
| Yet another example of something I have been known to harp on about! Namely, the poor quality, cheap materials used and poor production of the replacement product we are forced to buy. One hopes that brake parts are made to a higher standard!! |
| Allan Reeling |
| Well spotted Simon - I'm impressed Something like that can take ages to find and not something you would necessarily check on a new pump I'll certainly be peeping in there on new pumps from now on Thanks for sharing this with us Cheers Willy |
| William Revit |
| Simon. If you dumped the stop leak into the overflow tank (expansion tank), you have, quite probably, sealed the copper hose that goes to the bottom of the tank. This hose is connected to the line from the radiator and allows the coolant to flow back into the radiator as the engine cools down. If it is blocked, you have a sealed system (radiator and engine block) which can build up pressure until a hose bursts. You might want to check out the expansion tank before starting up the engine. Les PS An oil and filter change, after running the engine so hot for so long, would be a splendid idea. |
| Les Bengtson |
| Well, the car is now fixed. I checked things weren't blocked and put her back together. What a difference! I went for a test drive intending to go to the useless car parts place to get new coolant, oil and filter as Les suggested. They were shut making them even more useless than usual. The difference to the car is amazing. The temp never went above 80C on the gauge (mid way) whereas before it was always up around 100C. Since it was evening I tried the heater. That made an amazing difference. It worked! There was more heat from it than ever before and the temp on the gauge also dropped another 5C. The cooling fan never came on either when I am used to it always being on. I need to tweak that a bit to get it coming on and off at a sensible temp now. When I got home I checked for leaks. Nothing. Everything looks good. In the weekend I will go and buy new oil and filter as well as coolant and radiator flush and change all her fluids. On the way home I also popped into a bottle shop for a nice bottle of red to celebrate and top up my fluids! Amazing what difference a working water pump makes! Bit embarrassing the car has been on the road for exactly 2 years before I realised though. Thanks for all the help! |
| Simon Jansen |
| Excellent! Running hotter than one might expect (even if not actually overheating i.e. losing coolant) is not unknown on rubber bumper cars, I'm wondering if this partially blocked pump port is fairly common. |
| PaulH Solihull |
| Well, that's a new one for me. Just when you thought that you had seen everything, something like this comes along. Good work on figuring out the problem. RAY |
| rjm RAY |
| Isn't it great how these little experiences enrich our lives! And thirty odd years ago without the 'Net', we would never have been able to 'share'. We are now much wiser. ( I'm pulling my pump off this weekend!) Mike |
| J.M. Doust |
| Gee Simon,that was quite a ordeal.How is your other auto comming?,Rich O |
| rich osterhout |
| I did several long, fast drives in the weekend and the car is running great now. The temperature is much better behaved! The other car, my little Austin 7, is coming along slowly. Still working on getting the body shape right. It's steel tube with aluminium skin and there isn't a lot of tube there! Even so getting the shape just perfect takes a lot of playing. Especially when you're doing a shape that hasn't been done before. http://www.asciimation.co.nz/austin7 Am also looking at supercharging it when it is all done. Simon |
| Simon Jansen |
| I've been busy lately and came to read this late... really interesting problem, great suggestions, and I appreciate the fact Simon, that you posted the answer. Good Job Simon! |
| Dave Braun |
This thread was discussed between 15/04/2012 and 23/04/2012
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