MG-Cars.info
MG MGB Technical Coolant pressure BBS discussion at MG-Cars.info
MG-Cars.info
Welcome to our Site for MG, Triumph and Austin-Healey Car Information.
Recommendations
Parts
MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.
MG MGB Technical - Coolant pressure
| Looking through the archives, I couldn't find an answer to this one. How "expanded" should the top radiator be after a 10km run with the engine at normal operating temp? I had cause to open the bonnet after a run , and the hose was very swollen looking. Was back to normal a couple of hours later when I looked. I have a 7psi rad cap. Cheers John |
| John Minchin |
| John It shouldn't blow up much at all If it's blowing up it needs replacing -- gone soft Also check that the cap is the correct one for your radiator as there are a few different lengths available If for example you have a long cap in a short radiator neck the pressure will go sky high willy |
| William Revit |
| What Willy said. Your hoses should show no noticeable swelling when hot and pressurised. |
| Mike Howlett |
| After fixing cooling system problems on my cars I've carried on monitoring the pressure for a while, mixed driving is about 5psi, getting up to 8psi with a bit of 'brisk' driving i.e. the pressure should be nowhere near cap pressure except under extreme conditions. That is enough to give slight swelling, especially with plain rubber hoses i.e. no embedded sock, but it shouldn't be obvious. Some cooling system problems can pressurise the system to cap pressure and hence swell hoses more. For years my rad overflow was always hissing when switching off a hot engine, and dipping the end of the overflow pipe in a cup of water showed bubbling. That soon slowed and stopped, then hissed differently, as it started sucking air back in. Eventually - and I mean after something like 20 years - I did start getting coolant loss, a combustion leak check of the radiator showed the head gasket was leaking, and replacing that stopped the coolant loss as well as the hissing. Interestingly enough both cars when I got them showed slight temp gauge oscillation during warm-up, which as both did it I ignored. But since fixing problems on both many years later, neither now oscillate - just slowly rise during warm up, then sit there while driving. Of course they do go up when stuck in traffic, especially in summer, and back down again when moving again. Many fret about that, which is why modern cars have processor controlled temp gauges that resolutely show the same temperature regardless of conditions, unless the actual coolant temp moves out of the acceptable range. |
| Paul Hunt |
| I checked the amount of water to bring level up into the filler neck - about 1.2 litres. The approximate volume of the top tank is a bit bigger, so the guess is that the vanes are covered so the correct quantity of coolant is in the system. However , after the last trip I also noticed signs of loss of water (I don't have proper coolant in yet :-( ). I checked and its not coming from the hose joints, the radiator, or the heater valve. Welch plugs look OK. Starting to wonder if I have a head gasket problem which might account for the expanded hose. But there is no evidence of water in the oil (based on appearance of the oil on the dipstick alone at this stage). Does this look suspicious?? John 
|
| John Minchin |
| I would say that stain does not look good. I'd guess the gasket has gone. If it has gone between a combustion "part" and a coolant "part" I would guess it could cause the expanding hose. Combustion leak test would prove it. |
| Michael Beswick |
| It looks like usual head gasket water weep on plug side of head. Maybe put a Payen composite gasket on and at the same time replace your thin head washers for the thicker ones? If you had blown the gasket from cylinder to waterway you would have blown all the water out of the rad not just pressurised slightly. Peter |
| Peter Burgess Tuning |
| Thanks guys A good start to the new year :-) Still, not a disaster..... John |
| John Minchin |
| Hmm Looks a bit sad, I'm thinking the head will be coming off, but have a good look and make sure it's not coming from up the front ,like out the bottom of the temp. sensor or something and running along the edge of the head till it finds somewhere to drip off Back to the hose swelling -- Even if that is a weeping headgasket the radiator pressure shouldn't exceed the blowoff pressure of the cap--7lb -- if the hose is blowing up anymore than about 1/8" over normal resting size, it's stuffed and needs replacing before it lets go and does preventable damage to your car. willy |
| William Revit |
| Given the arc of staining above the gasket, and the droplets liberally spattered around, it looks to me like it is squirting out at that point. You are in good company, in record attempts in the early days MG found that combustion pressure at full throttle was squirting coolant onto the plugs causing a misfire. As mentioned if a combustion leak is pressurising the cooling system you will get air escaping from the overflow, showing as bubbles if the end of the tube is placed in water. If so, you can then check with a combustion leak detector if it is combustion gases, as it could be from some other cause like the water pump seals or bottom hose letting in air. But that looks more like an external leak than an internal. |
| Paul Hunt |
| Interesting you saying about heads lifting under high power use Paul. These last two years we have found the endurance race Bs (around 170 bhp) start to lift the heads after 20 mins flat out racing, to combat this we use ARP head studs at 70lbs ft and Cometic multi layer head gaskets. We put it down to crap fuel. The problem does not occur with Sunoco blue fuel! Peter |
| Peter Burgess Tuning |
| I suffered from the head lifting, under hard use, a few years ago. I have the Moss supercharger system on my car and was doing a bit of spirited driving on a hot Summer day. When I got home, I checked all of the fluid levels only to find a small amount of oil in my radiator. I had overhauled the engine back in '93 and it's always run perfectly. I pulled the head, chamfered the head stud holes, installed a Payen composite gasket and a set of ARP head studs, washers and nuts. There's been no leakage problems since. Simply replacing the head gasket and not putting in new, that is ARP head studs, will lead to a future head gasket failure. The factory studs are well over four decades old now and have gone through millions of heating and cooling cycles. They don't hold up forever and the standard ones, on the market today, have a less than stellar record. RAY |
| rjm RAY |
| Thanks again. I will check the overflow tube for bubbles. I'm sure I will be back online for further advice before I start head removing. |
| John Minchin |
| Just had a thought. Would a retorque be worth a try? I assumed that this had been done prior to my ownership, but maybe not. Given the low mileage, it would be overdue if not already done. John |
| John Minchin |
| Better to pull the head and do the job, then you will know it has been done. Remember to use a Payen composite gasket. Peter |
| Peter Burgess Tuning |
| Thanks peter I've commenced sourcing the gasket. I'm intending to also get new studs, washers, nuts as well as I don't know the history of the current parts. I knew there was a good reason I purchased a torque wrench years ago! John |
| John Minchin |
| John, Check that area between 2 & 3 for possible cracks under the layers of paint. |
| Allan Reeling |
| So, For the job I will need - Head gasket Studs, washers, nuts Pushrods oil seals Thread lubricant New radiator top hose Engine oil Sump plug gasket Should I also have on hand - Thermostat housing gasket Exhaust manifold gasket Carburettor gaskets Rocker cover cork seal Or should I just replace them as a matter of course? (As you can tell , I haven't done this before!) |
| John Minchin |
| John Interesting list We'll go through your list- Headgasket - yes Studs,washers nuts-- If you are getting an ARP set, all these will be in the kit--If you are getting studs seperate then you will need to make sure that you get good quality, thick,hardened washers--ordinary flat washers from the hardware store won't hack it. An option for these is to go to your local engine reco machinist and get some from one of the Japanese diesel engines, which have nice thick rock hard washers -Nuts can be reused if the threads are ok --Really an ARP set, while being a tiddle expensive is a good option Pushrod oil seals-??? no such thing, -I'm guessing you mean valve stem seals--If you get a Valve regrind gasket set instead of a bare headgasket, these will be in the kit Thread lubricant ARP stud kits come with their own lubricant If not using ARP engine oil will do the job just fine Top Radiator hose - yes get one Engine oil/sumpplug washer--only if you are intending to change the oil--Changing the oil isn't a necessary requirement for doing a headgasket job so long as it's ok and you drain the radiator before you start removing the head to stop water getting down into the oil. having said that, it is nice to have it all new for a fresh start if that's what you are thinking- Manifold gasket thermostat gasket tappet cover gasket----All you need here will be in the VRS (valve regrind set)gasket set A very important thing for you to do, which no-one has mentioned, is to get the head checked with a straight edge for flatness--and also have a real good look at the surface of the head around water holes etc Get your machine shop to check it out for cracks/corosion and get them to fit your new valvestem seals while they have it--Depending on the condition of the surface of the head it might need a skim My personal choice is to give them a very light skim anyway unless it appears like new ,just to remove any irregularities As it's your first, I strongly suggest you get the head examined by someone in the trade--- If you know of David Short in Hobart -he would give you an honest opinion of the condition of your head and tell you the best place down there to take it to for machining etc--Actually ,he might be your best option for getting your parts, at least he knows MG's inside out and what not to get Good luck, keep us posted willy |
| William Revit |
| And one extra thing. Countersink the top of each head stud hole about .040" as they do "pull" over the years and can affect the new gasket seating. (Important) A touch with a 1/2" drill bit works fine. Denis |
| Denis4 |
| Thanks Denis and Willy My mistake - valve stem seals I will get the head checked. Just about to order parts. Any tricks to getting the old studs out? |
| John Minchin |
| Two head nuts tightened together usually works well. The new ones only go in hand tight. I usually screw them in all the way then back,um off 1/4 turn Denis |
| Denis4 |
| *Definitely* don't torque studs into the block! You will likely crack it. |
| Paul Hunt |
| Noted! Anyone know where I can get an ARP stud kit in Australia? Having trouble finding anywhere online at the moment. One place can get them - 8-10 weeks delivery That would mean missing out on summer driving 😓 Cheers |
| John Minchin |
| John I got my last set from Fabre Australia, try them, but even from the USA it's only 7-10 days. Moss, APS, have them or even ARP direct although that may take longer. Denis |
| Denis4 |
| B-Series Cylinder Head Stud Kit, 200,000 PSI Rating, With Rocker, Studs, Nuts, Washers Manufacturer: Automotive Race Products Part No: HSB42 |
| William Revit |
| Sorry I didn't mention That was from Aptfast - USA and probably a unique part no used by them also British parts northwest -USA Cylinder Head Stud and Nut Kit HD MGA MGB Part number: TMG10764 Availability: In stock Qty: $175.96 |
| William Revit |
| Well, just got a window of opportunity to get the head off and have a look. Cant take the head right off yet as the Temp gauge sender retainer is seized in the head so I'm waiting on the penetrant to work. But I gopt a horrible shoick when I took the rocker cover off. Then the head bolts seemed quite loose , and as the last few were removed, the head popped up a couple of mm from the block Here are some pictures. I'm worried what the cylinders will look like :-( 
|
| John Minchin |
| And a view of the head-block gap. By the way, I rechecked the dipstick and there is no evidence of water there 
|
| John Minchin |
| John, If the rocker shaft was still in place when you slackened the head bolts, the valve springs will lift it! But that first picture is horrible, never, ever seen anything like that even on very jiggered engines! But young P B has, no doubt, seen something similar. Lots of water and/or combustion contamination, by the look and probably totally blocked crankcase breathing. Interested to see the cylinder condition and crack test results, but when you say the head bolts were "quite loose", was this finger tight, easily undone with a ring spanner, or what? The gasket will indicate blow past and leakage. |
| Allan Reeling |
| You can "persuade" the temperature sender bulb out by removing the thermostat housing and the thermostat. You can then gain access to the back of the bulb and gently push it out. RAY |
| rjm RAY |
Allan Not finger tight. But socket and handle with not a very hard pull. One stud screwed out of the head quite easily. But the stud looks ok - no sign of stretching or thread damage. Ray, the retainer Nut is tight in the head - so far penetrant hasn't worked. I will try a modified ring spanner with a slot cut in it. Worst that can happen is the spanner will break. Last resort (s) apply a bit of heat ( that will probably cause damage anyway), or cut the tube and replace the gauge and tube later :-( John |
| John Minchin |
| Crikey, what strange mess. That doesn't look like ventilation problems to me, the coating seems to be too evenly distributed, even showing the rocker adjuster screw slots. On engines I've seen it on it just multiplies and goes everywhere, and has been brownish rather than the very white appearance of that. Does it wipe off? |
| Paul Hunt |
| John, Apply heat with a heat gun, it's a lot safer than a flame!! The studs often come out while trying to undo the nuts. The nuts can rust and they are often gummed with paint. |
| Allan Reeling |
| yes, the nut was clogged with paint - took a bit of effort to get it off the stud The grey coating I would describe as a "mousse". Next morning the moisture had evaporated off and the springs and tappets just look oily (ie like normal) Likewise the inside of the valve cover is just oily now. John |
| John Minchin |
| Head off being crack tested, skimmed, hardened valve seats etc. by it looks like it was just a loose head ( ie not re torqued after run in) HAd to cut the temp tube as the retainer nut would t shift :-( So the gauge is off to be repaired. A benefit of having the head off - I can see that the front carb is too rich, so a readjustment will be on the list John |
| John Minchin |
This thread was discussed between 04/01/2016 and 20/02/2016
MG MGB Technical index
This thread is from the archives. Join the live MG MGB Technical BBS now