Thermostat Alfa 90 2.5l

[The Count]

I need to replace the thermostat on my 1985 Alfa 90 2.5 litre.
From what I've read, this comes as a complete unit with the housing and thermostat but I have also seen a Tridon thermostat and big square gasket to suit advertised. Can the thermostat only be replaced in my current housing or do I need the complete unit (and if so, are they available in Oz?)
Thanks
Nick

[VeeSix]

Internals can be swapped over 

[The Count]

OK... Now ready to do thermostat replace.
Looks like there may be some issues accessing the bolt heads (3X) to remove thermostat housing as the timing belt covers may get in the way. Is it easier to remove the covers (or split at top and pull aside) before removing thermostat housing?
Has anyone done this leaving covers in place...looks like it might be possible with skinny sockets???

[The Count]

Thanks... Went with Tridon thermostat so hope that the modification to fit it is not too difficult.
Looks like the housing has been accessed before so I'm optimistic that I'll get the bolts out fairly easily.
Will follow your suggestion and go with the front one first. Wonder if using my cordless drill with the rattle feature might help if the bolts are very tight?
Nick

[The Count]

At long last got around to replacing the thermostat in the 90 (2.5l V6) with the Tridon replacement unit following the how-to above.

Went pretty well but (as mentioned) the slight "lip" on the Tridon thermostat means a very careful refit and thick gasket otherwise the cover leaks as mine does just a little.

HOWEVER... once fired up, the engine continues to overheat.

Have checked the following:
Water pump working well
Thermo fan and fan thermostat switch operational but kicks in VERY late

It seems that the radiator core may be the issue here as the top half of the radiator gets VERY hot but the bottom half (where the thermo fan thermostat switch is located) takes a long time to reach the 90 degrees necessary to turn on the fan. By the time this happens, the top half of the radiator is near boiling.

Is it worth a radiator flush treatment or do I go ahead and replace the radiator (I have been offered a spare one)?

I'm also thinking of reverting to the standard thermostat rather than the Tridon so I don't have to manage dribbles from the thermostat housing.

Thoughts?

[dehne]

Anyone have pics of this

[The Count]

dehne...

Sorry this has taken a while but today had to pull down the thermostat housing on my 1985 90 GCL (2.5l v6) so was able to get a picture of the thermostat housing modified to accept the Tridon thermostat. As you can see, the Tridon unit is slightly larger than a perfect fit into the housing and it also has a flange with a little lip on it so that it sits proud of the housing. This means using a double gasket which is not ideal. Better perhaps if you have the facilities to machine out the recess in the thermostat housing so that the lip fits into the recess allowing a better gasket seal.

Hope this helps and if you need to find out more or more pics, please PM me with your email.

Cheers,

Nick

[dehne]

Thanks for the pic, I have a couple of thermo units so I might have a crack at doing the recess in it.

[The Count]

Latest sitrep...
Have drained and flushed cooling system and removed the Tridon thermostat (as a temporary measure and to stop small leakage).
Pleased to report that the 90 now runs at slightly under normal temperature (in a Tasmanian summer) during all cruising and freeway conditions, the chin spoiler (now repaired and refitted)adds its airflow over 80kph but the engine still tends to run over the 90 degree mark in stop-start traffic. The thermo fan is operating correctly as far as I can ascertain and the water pump is all OK so that still leads me to think the radiator core (despite flushing) may be at fault.
Has anyone else had this experience?

[four90s]

Danger Will Robinson, danger.

From the number of 90's and 75's that I've had through my hands, there seem to be two different thickness radiators about. The thin one (I'm assuming a single core job) has a core about only 20mm thick, while the thick one is about 40mm. Importantly, the tanks are the same size for both of these, so you need to check.

Not sure which cars got what, but check that out. There are some thicker (about 45mm) aftermarket radiators about which do a much  better job.

Hope this helps with your problem.

Regards
Steve
Adelaide.

[The Count]

Thermo switch is fine.. Brand new one only just installed.
Re radiator cores, have measured and mine is the narrow one (around 20mm). Wondering if..
(a) The broader core radiators are still available and have the same mounting points and
(b) Are the aftermarket units a bolt-in or do they require some modification to fit?
Yours in hope
Nick

[four90s]

Hi Nick,

The after market ones mount up the same and I do recall buying one new a few years ago.
You could check with your local radiator guy and if they don't have a listing for the 90, get them to check for a listing for the 75, as the radiators are the same and mount the same.

I'll check if I have a spare one still, if you are interested in second hand.

Regards
Steve
Adelaide.

[The Count]

Steve,
Can get the 25mm online but can't see the 35mm version in Oz even though I can find it in the UK.
Is the extra thickness worth it in terms of cooling efficiency?
Will also check local radiator specialists for a compatible unit.
Nick

[Domenic]

Have you checked with the Alfa club sponsors??