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MG Midget and Sprite Technical - Losing coolant
| Hey guys, I have a perplexing issue with my 1979 1500 midget. I am losing coolant, quite a lot. About half the radiator in a 20km trip. I suspect head gasket but engine running well, oil clear and I have not noticed any steam/white smoke in exhaust. I took the car to the local mechanic to do pressure test on cooling system and exhaust gas test. The mechanic said that the exhaust gas test is not reliable when the overflow/reserve tank is lower than the radiator top. While doing the pressure test, he noticed quite a bit of coolant on top of the gearbox case and said that the heater box is probably leaking. I have just removed the heater box and everything looks dry inside. How would coolant get on top of the gear box? Also, I suspect that my radiator cap is leaking. How can you test the cap and/or overflow tank opening? Thanks, Steve nb. my car seems to have a radiator from a 1275 car. Should I be upgrading? In normal usage, the temp stays cool whilst driving (regardless of ambient temperature) however gets hot very quickly in stop-start traffic, especially during summer. I have original engine fan. |
| gusangora |
| Steve. As my car is an A series powered one I'm not that familiar with the Triumph engine, but could there be a core plug leaking somewhere? I do know that the A series has one in the back of the block which obviously can't be seen without removing the back plate. Maybe the Triumph has the same arrangement. Look at the bottom of the joint between the engine and gearbox for signs of coolant. Bernie. |
| b higginson |
| Check hose clips on heater matrix are tight (ie. are right size and done up OK). If you let the car idle, you should be able to see the leak when hot (say 15 mins). A |
| Anthony Cutler |
| I agree with the core plug story, it is a good chance Regarding your getting hot when stationary, does the 1500 Midget have a viscous fan fitted? anyone before I go and check? |
| Robert (Bob) Midget Turbo |
| "does the 1500 Midget have a viscous fan fitted?" Early ones didn't, late ones did. |
| Deborah Evans |
| " I have just removed the heater box and everything looks dry inside " Perhaps the evidence of the leak evaporated during the removal time? Now that you have the heater out it's easy enough to bypass the heater and go for a drive and check coolant level again. As Anthony says, any leak that large should be visible, at least where it's dripping to earth. R |
| Richard Reeves |
| If the cooling system is the same as the later crossflow A series system then one possibility is that you have a weeping fire ring seal and the cooling system is being pressurised and forcing coolant out of the expansion tank. I had that problem and a temporary fix was to move the expansion tank take off from the left to the right side of the radiator. The original take off point means that coolant is forced out of the system when pressurised , whereas taking it out by the radiator filler plug means that the take off is in the outflow header tank and the exhaust gases accumulate at the top and can be vented to the expansion tank without loss of coolant. That worked well until I welded the small problem area on top of the block causing the weeping seal. |
| David Billington |
| Water pump going bad and weeping....thats always a hard one to see....and the last place i always look. As to the rad cap.... if its older then 3 years replace .... i always do this when i replace the statp |
| Prop |
| Thanks for the suggestions so far. I removed the heater box and matrix last night. I filled the matrix with water and let sit overnight. It doesn't seem to have leaked, but it has only ever leaked under pressure (ie whilst driving), never whilst sitting. Can I bypass the heater by simply connecting the hose from the heater outlet to the engine outlet, which had the hose that went to the heater tap? This will obviously bypass the heater, but is it okay to bend and twist the existing heater outlet/return hose to fit? ie will it damage the hose? All the hose connections are tight and leak free. I did try turning the heater tap off and going for a drive, but still lost coolant. The tap leaks if turned whilst engine running, but not when fully on or fully off. I sprinkled corn flour around the tap and heater hose connections so that I could see whether any coolant leaked out during the drive. It was perfectly dry despite the large coolant loss. Mine is a 1979, so should have a viscous fan (according to Deb). Best way to test? I just tried to turn it (with engine off and cold) but it wont budge. Steve |
| gusangora |
| you really need to pressure test this system My mate built a system pressuriser/pressurisor by drilling a hole in a rad cap small enough to take a Schrader tyre valve, taking out the proper cap and fitting his cap He used a plain nonvented cap, simply removed the gubbins in the middle of it, ensuring there is a rubber rim seal A few pumps with a foot pump will add pressure to the system and you can sit quietly waiting for the leak You need to be careful when pumping, use a tyre gauge and ensure you dont exceed the system's normal pressure (i.e if the normal cap has 8psi on it, stick to that) If there is a head gasket leak or a hose failure or a, well whatever, checking the pressure later will confirm (or you can borrow my expensive, pump and gauge included with multiple adapters device that cost a couple of hundred quid to do the same thing) Actually that isn't true, you cannot borrow it, I gave it back to the AA and always use Dave's device if I have issues to test out... |
| Bill 1 |
| Hey bill, I was wondering....with your homemade idea...can food coloring be added to help identify the leak.... or any better idea...i got to make me one of those.... been meaning to. |
| Prop |
| Why do you think you have a radiator from a 1275? 1275 crossflow rad has connections at top left and bottom right. 1500 rad, the connections are both on the same side - can't remember which. Easy to check. |
| Dave O'Neill 2 |
| Dave, that's why I think it's a 1275 radiator. Top hose connection on passenger side and bottom on driver side, with filler screw at top on driver's side. Also, hose to overflow tank on passenger side but overflow tank located on driver's side. When I bought the car (last year), I took it too an MG garage to get head work (needed new valves anyway) and they discovered that radiator had a sealed core and needed reconditioning/replacing and conveniently had one in stock! It now seems ghat they had the wrong one in stock! |
| gusangora |
| Yepp that does sound like a crossflow 1275....dont you hate it when you get screwed like that....may have been mistake or might have been intentional....but the effect is still the same, You might give Mark T. a shout, he might be able too arrange some type of swap being that its fairly new at a year old....i think he is on the gold coast |
| Prop |
| " I did try turning the heater tap off and going for a drive, but still lost coolant. " IIRC, the heater INPUT is blocked by turning the tap off, but the outlet is still open, therefore pressurized, i.e. a compromised heater matrix could still leak via backflow under pressure. R |
| Richard Reeves |
| Prop - wish Mark was closer but at just over a thousand miles, he is a bit far away to drop in. Richard, I believe you are correct. I have now bypassed the heater (using the hose that went from tap to heater, it was a good fit to go from engine out to engine in). Will run shortly and report. I am not sure whether I should bother replacing the radiator. It must work, because the engine never gets hot when on the highway, only when stuck in traffic? Or would the bigger radiator also help that? I'm thinking that I need a new fan, probably electric (Kenlowe, Revotec). |
| gusangora |
| 1000 miles !.... i keep fogetting oz is not a blip on a map |
| Prop |
| Okay, test results. I went out and bought a new radiator cap, which is a much tighter fit than the old one (actually hard to tighten and remove). No more coolant leaking or being pressured out of the cap nor overflow tank - Problem 1 solved. I bypassed the heater matrix and ran car up to just above half-way on the gauge (normal is quarter). No visible signs of leaks anywhere. Increasing revs to 2000rpm lowered the temp. Allowed engine to cool then removed radiator cap and filler plug. Some pressure escaped when cap removed but coolant level in overflow tank and radiator both as per prior to test. This rules out head gasket, leaking hoses and core plug leak. I now assumed that the heater matrix is leaking but also changed radiator cap, so decided to test heater matrix. I connected the heater matrix without installing the heater box, so that I could see any evidence of leaking. The heater matrix did not leak however I discovered that the heater tap was leaking heavily. Strange that it didn't appear to leak when I covered it with cornflour (although that test was only with the tap off). Anyway, I now need to recondition the heater tap - Problem 2 solved. I read somewhere that it's just a matter of changing some o-rings and creating a new gasket. In any event, the heater box now has a nice new coat of paint (flat black), so not completely futile waste of time. I did discover a new problem, but will start another thread for it. The front carb float chamber overflow was spitting out a lot of fuel while warming up the engine. Normal? Thanks again for the advice. Steve |
| gusangora |
| Most likely the float needle sticking or clogged...vary common...bang on the float chamber with a plastic screw.driver handle and see if that corrects if not pull the float chamber cap off and clean the little needle and check for proper spec of the float Sounds like just a worn rad cap... id try to make a new gasket for the shout off valve and see ... sometimes its easer and economical to just buy new....i wasnt ever able to rebuild mine....in the mean timme just open it up and let it run freeflow....might be able to jjerry rig something in the mean time Btw....congrats on getting it sorted....good thing you dontneed the heater for months from now |
| Prop |
| Most likely the float needle sticking or clogged...vary common...bang on the float chamber with a plastic screw.driver handle and see if that corrects if not pull the float chamber cap off and clean the little needle and check for proper spec of the float Sounds like just a worn cap... id try to make a new gasket for the shout off valve and see ... sometimes its easer and economical to just buy new....i wasnt ever able to rebuild mine....in the mean timme just open it up and let it run freeflow....might be able to jjerry rig something in the mean time Btw....congrats on getting it sorted....good thing you dontneed the heater for months from now |
| Prop |
| It seems that I spoke too soon! I have removed the heater tap and cleaned it up ready for new o-rings, but all the plumbing supply places are closed for the long Easter weekend. I read somewhere that there are supposed to be 2 o-rings but mine only has one? Anyway, I bypassed the heater again and went for a drive, not expecting any issues. Sure enough, after about 10km, the water temp gauge starts rising. I headed back home, and by the time I arrived, temp was just up to 3/4. Looking under the hood, I could see that a lot of coolant had escaped via the overflow/expansion tank and/or radiator cap. Now, I don't know whether the coolant expansion tank is faulty (strange that it didn't leak before, when I tested with car idle until temp half way?) or whether the idea put forth by David Billington is correct (coolant being forced out by exhaust gases)? Guess I will have to bite the bullet and let the mechanics have a look. Steve |
| gusangora |
| One last thing to try.... with the engine cold fill the coolent and let the engine idle with the rad cap off for about 1/2 hour....sometimes on these little engines air gets trapped and gums up the works.. and does what you discribe Also.... i always have to retighten my hose clamps about 100 miles later when putting new hoses on....might give that a look also |
| Prop |
| The overflow/expansion tank's hose connecting tube can come loose where it is "joined" to the tank wall, rendering the tank useless as a pressure vessel. If yours can be wiggled at all it might be your problem. The (blurry) pic shows just such a broken joint up close.  |
| Richard Reeves |
| I took the Midget back to the garage for a head gasket/exhaust gas test. Initially, it was negative but after a couple of minutes the liquid colour - HGF confirmed. So now I have to buy a gasket set and learn how to replace the gaskets. Any recommendations for gasket for 1500? What will I need? Thanks, Steve |
| gusangora |
This thread was discussed between 22/04/2011 and 27/04/2011
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