heater efficiency water cooled

[Bryan]

Me again, cannot seem to find the answer in the history files. On my T25 1988 water cooled the heater never gets really hot as on a modern car. The engine gets up to temp as the electric fan kicks in but even running the engine at reasonably high revs ( which helps) it still only blows warm. The inlet hose to the heater matrix gets hottish but you can hold on to it without any real discomfort so not that hot. Is it that these heaters are not very efficient or do I have a problem with the valve behind the radiator which I believe from the service history was replaced some years ago.

[Reimotim]

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I found my matrix was blocked with a lot of leafy mouse nest debris. Worth a check if you're gonna have the dash out any time soon!

[AdrianC]

The inlet hose to the heater matrix gets hottish but you can hold on to it without any real discomfort so not that hot.

Is this felt at the dash end, or at the rear? The heater takes it's feed from the coolant tower just in front of the NSR wheel. The stub for it crumbled and collapsed on ours - maybe yours has been bodged and there's restricted flow? It should get sufficient flow to be properly hot - same temp as the rad - once the heater valve's been fully open for long enough for hot to flow through properly. Might also be worth checking that the dash lever is operating the valve properly, all the way.

Modern heaters are air-blend - the matrix gets full water flow all the time, but the amount of air passing over it is varied. Ours are older-style - the amount of water varies, so it'll take a while (especially with the big long pipework run) to get hot water all the way round. It's also why we need to make sure the heater's on full hot whenever changing or filling the coolant.

When did the coolant last get changed, and how filthy was it? Might be that the matrix is partially blocked, so flow's reduced, hence the pipe not getting properly hot at the top.

If the pipework's not hot, then I don't think your (main) problem's the same as Tim's - he'd have been getting full hot to the matrix, just no airflow to then pass that heat into the interior.