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Car Forum / Jaguar Cars / May 2005heating problem
My 1970 XJ6 has developed a heating problem. For some time now the heat gauge rose up to 75% when the car is driven, but now when I switch off the motor a lot water steams out of the reservoir. There is no radiator cap, this area appears to be sealed by the previous owner. The reservoir has just a plastic cap (no pressure release). The car is mostly driven for 30 minutes weekly and now when it is used for 60 minutes or so, there seems to be a problem. Any advice on on checking the water pump or oil dip-stick for certain signs and the radiator? Thanx in advance! Vassie > My 1970 XJ6 has developed a heating problem. For some time now the heat > gauge rose up to 75% when the car is driven, but now when I switch off the [quoted text clipped - 7 lines] > Thanx in advance! > Vassie My advice would be to take it to a radiator shop and let them check it over. Obviously the car needs to have it's original pressure relief valve restored, but the symptoms you describe could be caused by a water leak in a hose or radiator, a radiator flow problem, a bad water pump (pumps usually leak and/or get noisy when they fail), or a stuck thermostat, among other possibilities. The radiator has been tested and I believe there is a head gasket leak. There is no evidence of oil on the dip-stick. Do I have to take the cylinder head out, or are there any quick fixes. The setup of the radiator without a main radiator cap is satisfactory according to the repair shop, he says the modification is fine. As explained, this heating problem has gradually increased over time. >> My 1970 XJ6 has developed a heating problem. For some time now the heat >> gauge rose up to 75% when the car is driven, but now when I switch off [quoted text clipped - 13 lines] > usually leak and/or get noisy when they fail), or a stuck thermostat, > among other possibilities. > The radiator has been tested and I believe there is a head gasket leak. > There is no evidence of oil on the dip-stick. Do I have to take the > cylinder head out, or are there any quick fixes. The setup of the radiator > without a main radiator cap is satisfactory according to the repair shop, > he says the modification is fine. As explained, this heating problem has > gradually increased over time. Sounds like there may be a leaking head gasket like you thought. Check for bubbles in the coolant with the engine running. The gasket fails between a cylinder, often #2 (second from back) and the water passages, you won't find water in the oil. This failure causes some coolant to be drawn into the cylinder on the induction stroke and the cooling system to become over pressurised as the fuel/air mixture is forced into the water passages during compression. To test, first remove the radiator cap, take out all the spark plugs and do a compression test. Coolant will overflow or shoot out of the radiator filler neck when you get to the faulty cylinder. If you don't have a compression tester, just try it with one plug fitted, the engine turns over faster with the plugs out. That's how I found mine was faulty. Let's know if you have to pull the head off, no quick fixes, just be thankful it's a SI, makes it less complicated. BTW, the cap on the header tank on the front of the engine is normally not a pressure cap, but the one on the tank on the fender is.  Signatureregards, John Hudson Brisbane Australia 71 SI XJ6, 85 SIII XJ6 They can burn through to the water jacket. In that case, there will be no water in the oil. There is no easy fix. The head must come off. With the cylinder head off, check for warpage of both head, and cylinder block. The head is almost always warped when this happens. Steve R. > The radiator has been tested and I believe there is a head gasket leak. > There is no evidence of oil on the dip-stick. Do I have to take the [quoted text clipped - 20 lines] >> usually leak and/or get noisy when they fail), or a stuck thermostat, >> among other possibilities. Be aware that the head will need to be straightened before the face is machined. The cam shaft will be under stress otherwise. Chris >They can burn through to the water jacket. In that case, there will be no >water in the oil. There is no easy fix. The head must come off. With the [quoted text clipped - 40 lines] > > Pressure caps raise the coolant's boiling point, that's why they're used on all cars. The coolant should be a mixture of about 50% antifreeze and 50% water. The engine's coolant is at its hottest just after the engine is shut off. That's because it stops circulating and so has to absorb more heat from the cylinder head and block. So if the coolant is to boil that's when it will boil. So at shut down, without a radiator pressure cap, the engine coolant will easily boil. Prior owner may have wanted to "save" the $10 cost of a pressure cap or, hide a leak somewhere by not pressurizing the cooling system. Consider that restoring the cooling system may lead to further cost than a pressure cap. Check the dip stick. If there is coolant in the oil it will be obvious! With the engine cold, remove the spark plugs. Look for moisture and coolant on them. Either symptom indicates a burn through on the head gasket. I had the same problem with a MKIX many years ago. If, on disassembly, you find a burned path in the head gasket, check the cylinder head for warpage. Steve R. > My 1970 XJ6 has developed a heating problem. For some time now the heat > gauge rose up to 75% when the car is driven, but now when I switch off the [quoted text clipped - 7 lines] > Thanx in advance! > Vassie > Check the dip stick. If there is coolant in the oil it will be obvious! > With the engine cold, remove the spark plugs. Look for moisture and > coolant on them. Either symptom indicates a burn through on the head > gasket. I had the same problem with a MKIX many years ago. That should have read MKX. If, on disassembly, you find a > burned path in the head gasket, check the cylinder head for warpage. > [quoted text clipped - 11 lines] >> Thanx in advance! >> Vassie > My 1970 XJ6 has developed a heating problem. For some time now the heat > gauge rose up to 75% when the car is driven, but now when I switch off the [quoted text clipped - 7 lines] > Thanx in advance! > Vassie I have just replaced the radiator in one of my OHC 4 litre Fords , it tested fine and both mechanics testing insisted it was fine , but the classic symptoms of over heating over a modest speed and getting very hot when stationary after a short un ( less than 10k) indicated is was faulty , New radiator fixed it and now its running at 74 Deg V on the top hose. I would suggest either borrow a suitable radiator or seriously consider the damage resulting if it is faulty . |
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