405 heater not very warm

Heater not working correctly since blown head gasket changed.

The coolant system seems to be working ok. Temperature reading 90°,
radiator hot, inlet and outlet pipes to heater matrix hot, outlet pipe
to thermostat hot, then top hose from thermostat to radiator suddenly
changes from cold to hot which must indicate thermostat operating
correctly, water expanding in radiator which indicates pressure ok.

Only warm air is expelled through the screen and dashboard vents, the
lower vents in the footwell are virtually cold.

I have found two "valves", one on the thermostat housing and the other
just above it (5mm socket head) which I have undone hoping to bleed the
system; only water came out, no air was apparent.

Any suggestions of what to try next please?

 

Did you just open the screws/valves to bleed the system, or have you used
a 'topping up device' as you should have? The heater matrix is above the
height of the filler cap, so it will not be filled up completely by just
opening the bleed screws. You need a funnel of sorts, or manufacture one
yourself by cutting off the bottom of a plactic softdrinks bottle and
sticking it (watertight! use some duct tape) upside down into the
expansion tank next to the radiator. This way you can raise the coolant
level above the highest point in the system (which happens to be the
heater matrix) so it can bleed properly.
On the other hand, if the inlet and exit to the matrix are both hot, the
matrix could also be partly blocked, possibly by debris for the old head
gasket. In that case rinsing the system might work, or replacement is due.
My guess is that topping up will cure the problem, though, since it
appeared suddenly after the head gasket operation, and it didn't creep in
over time. This also rules out a failure in the flap that directs the hot
air to the screen, dash or footwell, according to the setting on your
console, methinks.

good luck!

 

Thanks for the info I'll give those suggestions a try. A replacement
matrix has to be the last resort, some engineer thought it was a good
idea to hide it behind the bulkhead :-(

 

Changing a matrix isn't too bad really, especially the Mk1 version (up
to 1993, radio aerial on the back wing). Remove the glovebox, drain
the coolant, remove the hoses to the heater pipes at the bulkhead
(engine side), undo the metal pipes to the matrix, and remove matrix.
Always renew the seals where the pipes connect to the matrix. After
1993, you have to undo the dashboard on the n/s and lift up to get the
matrix out. Best for two people.

 

Hello,

Radio aerial on the back wing, you sure ? I haven't seen one. I saw a lot of
both Mk1 & Mk2 405s, beginning with my ma's '88 SRi (Mk1, no way to be
wrong), they all had aerial on the roof.

 

Mk1 405 definitely had the aerial on the back left hand wing, Mk2 on the
front of the roof.

Neil

 

Hello,

So it must be an "export-specific feature", as all french-specs 405s had
aerial on the front of the roof, too.

 

Hi,

My -88 SRI definitely had it on the front of the roof...
The GRI:s also had this... Which model did you have?

I never had any heater problems though, the fan stopped
working and only blew in max position after a while..

Funny heater problems on my current 605, though... :-(

/Juhan

 

Must be an export thing or something, mine was a 1990 1.6GR. The reason I
remember the aerial was on the back wing is because I changed it for an
electric one. My mate's H plate (90/91) Sri already had an electric aerial
on the back wing, that gave me the idea of changing mine,

Neil