The fact the heater no longer produces hot air might be significant or coincidence. Sometimes a temperature gauge fault can produce the false belief an engine is overheating.
If it overheated while the coolant was leaking it is possible it loosened enough sludge to block the radiator and/or heater matrix. It could also have caused a 17 years old head gasket to begin failing. Below are some notes I prepared for my customers...
Cylinder Head Gaskets
A few explanatory notes...
The cylinder head gasket is a complex seal within the engine intended to keep cooling water, engine oil and the combustion process separate.
The life of a cylinder head gasket is very stressful and deterioration begins the moment a new engine is started for the first time and continues at a rate depending on the usage and the design of the engine.
It is almost inevitable that the cylinder head gasket will fail at sometime in the life of the engine and replacement will be needed.
Occasionally a complete head gasket failure is sudden (and disastrous for the engine as serious overheating can take place) but mostly symptoms or clues indicating the continuing deterioration of the gasket is resulting in it failing to do its job properly are present for a long time before complete failure occurs...
When two, or more, of the following symptoms are present most or all of the time it is time to seek help and advice: -
- Residual pressure in a cold cooling system.
- Pressure in cooling system immediately or very soon after start-up (while still cold).
- Abnormal amount of bubbles seen rising through coolant expansion bottle (if it is clear plastic) while the engine is running.
- Misfire occurring regularly on start-up that clears rapidly (cold or just-warm engine).
- Steady coolant loss but no external leaks.
- Abnormally large amounts of vapour from the tailpipe continuing longer than normal and might be accompanied by a spray of water. Some vapour and some droplets of water are normal, especially in cooler weather.
- Unusual or erratic heater operation (warm/cold not electric fan) often accompanied by unusual temperature gauge indications.
- Engine oil level does not fall in spite of usage or even seems to be getting higher: oil might also have a lighter coloured or creamy appearance than is usual.
- Oily residue floating on top of coolant.
- Emulsion present under oil filler cap and/or dipstick. Some emulsion (or mayonnaise) is usual for many engines under some circumstances.
Head gasket replacement is not a routine operation and it usually is not possible to predict the amount of work required before dismantling has taken place. For reasons of long term economy and reliability it might also be advisable to have other work carried out at the same time, such as timing belt replacement, valve stem oil seal replacement, etc.