Questions on coolant recovery tank...

Its a 1992 Volvo 740 GL turbo wagon. THe car overheated....didn't
get into the red, but got up above the usual mid-scale reading. I
found the coolant recovery tank was empty. When looking for the
reason why, I found the electric fan had shorted out. There is no
mechanical fan on this one, it has only a one electric fan about 12
in dia. The radiator and electric fan were not OEM, the motorheads we
bought the car from had replaced the radiator and rigged up a cooling
fan, probably not even off of a Volvo. So I refilled the reservoir,
and bought an electric fan of the same dia. (probably 12 in) and
installed it. The fan that was rigged up when we bought the car was
unshrouded, and about 2 in back from the radiator. Ths doesn't seem
good, as this allowed it to pull a lot of air in that had not flowed
through the radiator. The aftermarket fan I got from Autozone has an
integral shroud, and it is installed flush with the
radiator.Virtually all the air has to flow through the radiator.
Should cool better than the old one it seems.
So I thought I had the fix....yet when driven on hot summer day, it
started going up towards the red again. It lost coolant, as the
plastic recovery tank has a little crack in the top, near the overflow
return hose. THere was a high pressure build-up in it, enough to crack
it. But the gauge never showed but a little bit over mid-scale....yet
it must have reached boiling point to build up such a high pressure?
I am thinking the recovery tank cracked BECAUSE of a cooling
problem, and wasn't the initial CAUSE of the overheat.

Anyway, I didn't see any Volvo 740 coolant recovery tanks on Ebay, and
I don't want to pay the high price of one from the Volvo dealer. Is
there a generic or one from some other model that will work as well?
Is the cap suppose to relieve pressure on an overheat? It looks like
there is a valve (actually two) in it.

The radiator is definitely old, but the core is not rotten, and it
looks like the fins are not clogged up. It's a little hard to tell for
sure, as the AC condenser is in front. I dod check the
thermostat....took it out when teh engine was still hot, and it was
full open. So it is definitily not a bad thermostat.
Are there still such things as radiator specialty shops that could
flow-check the radiator? The car has lots of miles on it...it could
also be a bad water pump, I guess.
If the top hose is suppose to get stiff after starting the engine,
but while the thermostat is still closed, then there is not much water
circulating, because it is soft, it doesn't stiffen up from pressure
at all, it seems.

And yes, I did check that the new fan runs once the engine gets up
to operating temperature.

Come to think of it, back around May a mechanic got the AC
working again....then in mid-June the wife has the overheating event.
Two factors that would have put a lot more heat stress on the
engine...AC compressor and the weather!


Ideas?

 

The crack is more likely a cause of overheating rather than a result. And
with the crack, the system can't build up normal operating pressure and you
will lose coolant - both likely to cause overheating in the summer. I
recommend you focus on replacing the reservoir (and check the cap for cracks
that run along the sides) before turning your sights on the radiator.

The recovery tank is unusual in that it is pressurized; most recovery tanks
are past the pressure cap. But although cracks in the cap are common, the
tank doesn't often crack. Check Volvos in wrecking yards near you.

Mike

 

If you get really stuck, you can use plastic bond epoxy to repair the
tank for now, and I can grab another one the next time I go to the
wrecking yard, there's gotta be some yards near you though.

 

Yes, source a replacement reservoir from a wrecking yard, preferably a
U Pull It.

While you're there, consider buying the hardware to switch back to a
stock cooling set up (mechanical fan, shroud and ancillary bits: very
simple)

 

I like the electric fans personally, much quieter and they don't rob as
much engine power. Converting both of my Volvos is on the list.

 

http://fcpgroton.com/volvo240heatingcooling.htm

FCPGroton is a damn good place to order from. They have any part you
could ever need for cheap and they are all good quality. I just got
done rebuilding my 240s engine, and I gotta say, without their cheap
prices on good parts, I would have been stuck. They are nice too. I
kept ordering stuff because every time I looked at the car, I figured
out I needed something else, and they combined everything and refunded
part of the shipping cost that I was ready to pay 3 or 4 times for
because I had that many different orders.

the expansion tank is 24 bucks, for instance

 

Uh, that last post I referred to the expansion tank that goes on MY car
not yours. hehe.

here's the real link;

http://fcpgroton.com/volvo700900heating.htm#expansiontank

it's $39.50 for your car, sorry for the false advertisement!!

lo

 

James....I fixed the first crack abt 3/8 in long on top of tank near
the return line with automotive Goop. This is holding fine. But the
next time my wife drove it, and not even very far, it started to
overheat. My wife filled up the recovery tank as I had told her to do
if low, and she said water was running out along the tank seams. So
there is something very wrong here, must have built up a lot of
pressure. If that cap is suppose to open up on overheat to relieve
excessive pressure, so that the tank doesn't rupture, its not. But
again, it didn't ever get up to the red area.


So yea, I will get a coolant tank at local junk yard if
possible.....if not, buy one from you. I have a spare 740 radiator
from my now defunct '89 740...unfortunately we didn't save the coolant
reservoir before having it towed away. The spare looks in better
shape than the one installed now, so I think I better swap radiators,
and seal the recovery tank seam up with Goop, and see what happens.
Actually, with no shroud on the radiator, it would be possible to
put TWO of these Autozone 12 in. integral-shrouded cooling fans on
the radiator. But I have to be sure that the alternator and relay can
handle a second fan....and I don't know what the ampacity rating of
either is really. If you have some manual that gives the max ampacity
of the fan control relay, plse let me know. The fuse rating for the
control relay would be max amount, whatever that is. This setup
would be a lot better, seems to me. What do you think about dual fans?
I could easily set it up to turn on whenever the AC is switched on.
I know this shouldn't be done as a work-around for some other coolant
system fault...but once the system is properly fixed, seems like dual
fans would be a good idea for better reliability and relief from heat
stress.


I have the mechanical fan that was on the 89 740. There wouldn't be a
shroud on it if I installed it, and the lower hose from the radiator
is a problem, as it needs to be a couple of inches longer so it can be
positioned far enough towards the RH side of car so it will clear the
fan. Maybe is a bad idea if it makes it noisier and significantly
increases the load on the engine. I guess especially if I setup dual
fans its unnecessary.




Geronimo

 

Thanks, I will keep this parts source in mind...that is a real
good price. Might be better to just buy a new tank rather than an old
one. Geronimo

 

Geronimo
My two cents.
I had similar issues with my '87 744T.
Ended up being just a cracked tank for no particular
reason other then that it got old.

Replaced it and never had another problem with it.

don b.

 

The tank is still not holding. I know from experience the tank does not
crack even if the temperature gets into the red; at that point the cap
releases.

Mike

 

you might give some thought to the possibility of a leaking head gasket,
allowing hot gasses to escape from the cylinder into the coolant. This would
cause both overheating and an increase in pressure in the cooling system,
which could rupture the plastic recovery tank...

 

An the engine driven fan was last used on the 1991 models - a '92 would
have only had the later style 2 speed puller fan, like the front drive
cars. This fan is very effective at cooling (when it works).

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)