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Its not really a compression tester as the term is usually used. Its testing for radiator pressurisation, with a FSD of 5 psi, so it'd be more sensitive to damage than a compression test, but perhaps still not sensitive enough. Make sure your engine is off and cool, the vehicle is in Park or Neutral, and the parking brake is set.
Heater in a car acts the same as the radiator under the bonnet, which is why when the engine starts overheating its a help to use the heater in the car on max hot to help keep engine cooler
Right at the beginning of this thread I suspected CHG failure. I think paul 1963 (post above) is spot on. The symptoms described are a classic example of a tiny defect appearing. I try and be as cynical about garages as the next man, (though/so/because I have hardly ever used them apart from MOT's) BUT I think the innocent-until-serious-grounds-for-suspicion principle ought to be applied. sadly it is not that rare for head gaskets to fail again, you sometimes see cars advertised where it says head gasket just done suggesting that is a positive, to me it's a negative.
As well as the temperature issue, the engine seems to start struggling, stuttering/jerking a little when I am pulling away from idle or accelerating (particularly in low gears) after I have been driving for about 20-25mins, although varies depending on how hot of a day it is so I assume this relates to overheating? The motion is similar to that when you're close to stalling but not quite as bad yet. A colleague has suggested that it could be head gasket related, however this was previously ruled out by a mechanic (and I have hoped and prayed that it isn't as I don't want it to conk out entirely one day on my way to work/home). Any advice would be greatly appreciated as I am desperately trying to keep the car going until Sept/Oct when I will be looking to replace it altogether. The leak has definitely been repaired and despite the coolant bubbling after every trip to/from work, it doesn't look to have decreased in volume in the reservoir. The running temp (on the dashboard at least) seems to be normal, the only thing that's changed is that the fan boots in a lot sooner than it ever had done beforehand (I don't really expect it to have to come on for a 25 minute drive on residential roads). One thing I have noticed is that the fan doesn't seem to come on if I run the heater inside the car. Not entirely sure why this is, but in all honesty I know next to nothing about the internal workings of cars, hence why I went to a mechanic in the first place!If there was no overheating, the water pump replacement is a bit suspect, but is unlikely to have caused a head gasket failure, which seems to be suspected by the OP. unclip the two upper hoses by hand, unclip tank from the holding plates, drain in jar through the openings where you unclipped the houses, use the pliers to unclamp the main hose, pull the tank away from the hose. Install the new tank. Open the hood and locate the engine coolant reservoir. It is often a translucent white color, and has hose(s) connecting it to the radiator.
The reservoir has a fill range marked on the side. If your engine is cold, the coolant level should be up to the cold fill line. Note that I’m assuming a “classic” mechanical thermostat here. If its something more modern, perhaps controlled via satellite downlink from a CIA Cray Supercomputer at Langley, this may not be possible.)That'd be a false negative. Probably more likely than a false positive, which would require contamination with coolant or old test fluid Never remove the coolant reservoir cap when the engine is running or still hot. Let it cool down first.
You can buy products in Halfords to seal leaks. There is no need to drain the coolant, just remove enough from the filler tank and add and follow the instructions. There is a lot of pressure in the cylinder head so how effective a seal you could get here is debateable,I'd assume that'd be the chemical test for CO2, because I'd assume its commoner, but "some tests" isn't a specific description. I've done this a few times now on the Skywing. I don't much like doing it, but I think its less risky than your suggested laissez faire air alternative. It'll only do that if it leaks coolant into the combustion chamber, or blows its coolant out / overheats during testing. Nifty physical test for HG failure. I dunno if that would work with a lower tech pressure gauge (or even an improvised manometer) but it seems a possibility. Difficult bit would be getting a good seal. The mechanic I used took another look at it today and has returned it to me stating that it is in fact a problem with the head, stating he ran some tests and found gas to be escaping and entering the coolant system. He has now offered a short term solution by saying he can apply some sort of leak repair stuff which requires the coolant system to be flushed then the additive put in with new coolant. Does anybody have any experience with this and if so, how long is it likely to withhold? My car is due to have it's MOT in February, how likely is it to pass this?
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