I seem to have an ongoing cooling problem. Car seems to run ok without a thermostat fitted, but as soon as I put one in (it was a new item) and try and try to bleed the air out, it still runs hot and idling is all over the place (sometimes ok, sometimes it runs fast, sometimes it's erratic) It's as if the thermostat doesn't open as one side of the coolant pipe is cold and the other is very hot. Rad fan doesn't bring down the temp either. It's not the rad size either (it's a merc 190). When it gets hot the oil pressure also drops.

I did have it running slightly better sometime ago but engine temps were erratic so recently swapped the thermostat for the new one.

From what I've read problem is likely to be caused by an air lock? But if it is this, then I simply can't get the air out. I even had it up on a trolley jack for a couple of weeks which made no difference.


I'm running an omex 600 ecu.

Any ideas would be gratefully received.

Any one local to me who fancies taking a look or knows a business that would sort it out for me?

Cheers!

Those are the symptoms of not having a bypass connection to allow coolant to recirculate between the cylinder head and the water pump when the thermostat is closed.

Pretty sure I've git the plumbing the same as a lot of others have plumbed their 20v 4age engines but I'll double check...

Thanks.

I've hooked the two smaller outlets (heater?) on the thermostat housing together to make a loop, and also teed in the header tank there.
Haven't had any cooling issues, thermostat's working fine.
Bleeding is a little hard, as the two cooling lines are routed over the exhaust manifold, and thus a little high. Pressurizing the system a couple of times with compressed air make it bleed pretty good though.


I'd guess that without the loop there's no bypass and very little circulation at all, just the little pinch hole in the thermostat itself. This will cause the system to be very slow.

Rost
I'm using the same set up as you describe, except I've actually got a heater installed. The header tank feeds into one of these smaller pipes.

Note that the original Toyota thermostats, had a jiggle valve. If your replacement does not have one, try drilling an 1/8" hole to help bleed the air out of the system. The hole should be located at the top. I've also install a tee fitting at the highest point in the heater hose for final topping off [with heater valve open]. You also need a rad recovery tank, which you can plan on topping off 3 or 4 times until the system is completely filled. Dave W

An old style heater controlled by a water valve should have a by-pass cconnector to enable the coolant to take a short circuit round the heater valve straight back to a water pump inlet side. The fancy way of doing it is to use the SAAB 900 heater by-pass valve but two T connectors joined in an H configuration work just as well.


GENUINE SAAB 900 90-93 BY PASS VALVE - B202 -B212 - NEW - 4073706

[Edited on 9/7/16 by britishtrident]

The heater plumbing is quite simple with just an inlet and outlet, without any valves and simple small rad.

And the thermostat has got a jiggle valve. Wonder if I should bite the bullet and get a Toyota item for £38!