I have a Mk2 Coupe S with a GT engine conversion. When I'm using it on motorway runs or fast A-roads, the water temp never gets above 70 even when the weather is warm. In town or when I'm ragging it then water temp goes up to a more normal 90 ish degrees.

I was wondering if this is a normal occurrence for GT engines, or if not, if anyone else has had a similar problem. 70 is quite cold for a fully warmed up engine, I would expect it to sit nearer the 90 mark for regular use, and maybe a bit more in town.

I changed the blue temp sender recently so its not that, although I haven't checked the black one yet. Will check that, but anyone have any other ideas what it could be (assuming its not normal).

Maybe a Mk2 radiator is bigger than a Mk3 I don't know.

There are at least 3 different temperature thermostats. Also yours could be stuck open. They're not expensive so try another one.

my mk3 1.3 spi runs about the same temperatures and was wondering the same

thats about normal. Mine sits at 70 on cold days and 75/80 on hot days. Goes up in traffic though.

I'd say it's not 'normal'. 70C isn't really hot enough for most engines, and you should be looking at 85-90 for most of the time, even on the open road. As yeha suggests, try changing the thermostat. However, it could be the guage/ sender, like you say. Try and get the cooling fan to kick in, the first one should kick in at about 95C. If the guage is only reading 85C or something, we know that there's probably an issue there as well.

70C isn't really hot enough for most engines, and you should be looking at 85-90 for most of the time, even on the open road.

Yeah I agree, around 90 is a typical operating temp, and thermostats usually open somewhere between 85 and 95 (depending on setting). Can't believe I didn't think of checking the thermostat myself, especially with having had dud ones on 2 other cars. Must have been having a "special" moment when I wrote my post above.

Thermostat functionality is easy to check (start from cold then when its starting to get warm see if the top radiator hose is hot or cold) so I will do that, plus I will check (maybe replace) the black temp sender.

I'm still interested to know if this is a common occurrence amongst GT owners or not though.

Its a problem I've got to cure on my GT.

I replaced both black and blue senders, and ruled those out, as when stationary on the drive the the temperature climbs to around 95-100 at which point the fan kicks in.

With normal driving I struggle to see above 70 degrees and on motorways the needle can sit on the rest which isnt ideal.

Karl.

Don't rule out the black temp sender is unaccurate. Maybe it's the thermostat or the fan switch nees replacing or cleaning sometimes they build up sludge there.