Big, Black & Hot Sausage - Thermostat Top Hose Bypass

[Hardy]

Having an interesting problem with '99 4.0 - 130,000 klms.

Temperature needle went apeshit into the red after only a few minutes driving. I popped the bonnet only to see the top raiator hose was bloated to all buggery - looked like it was ready to burst.

The photos don't show how bad it really was. Yesterday was much bigger again. I replicated the scenario just now to take some pics by starting from cold and letting it idle for about 5 mins. Nothing happened so I increased the revs up to 2100 rpm and within 45 secs - gauge went into red and pipe started bloating.

This pipe runs from top corner of radiator into metal elbow that runs into the front of the valley.

I'm thinking there is some sort of blockage - but where and where to start looking?
Thermostat?
Water pump?
One mechanic suggested Head Gasket?




Thanks,
Hardy

[TRobbo]

that reminds me of a dead cane toad that's been sitting on a hot road for too long.

I'm with you, would start with the simple and most obvious - check the thermostat, then the waterpump and after that ??? unless you want to start pulling heads off give it to da man.

would be interested in your comment as to the problem when found

[Hardy]

Okay, I pulled the thermostat off. It's a 4-way housing jobbie with bottom hose on closed end, pump inlet & heater matrix on always open end and top hose bypass in the top middle where secondary valve is.

It's designed to be fully open @ 96 C so I poured some boiling water into it.
The main valve opens up okay but the secondary valve that is supposed to shut off the bypass line from top hose was apparently not working.

Looking at the direction of coolant flow with an open thermostat, this would seem to create a problem. Water coming out of engine (top hose bypass) is faced with water coming out of radiator. I would have thought the coolant would find a way despite open valve but maybe the pressures involved override this?

I'm prepared to buy a new thermostat ($140!!) if I have to and things are pointing that way but was just hoping for a little reassurance first.

Thanks,
Hardy

[Marty1]

Can you just leave the thermostat out and try it first?

[Maggot4x4]

Had the same prob on the weekend at LCMP, pulled the thermostat out and all was good. Must be the season for it

[Philip A]

This is one of the main reasons for 38A liner slips.
You would wonder why they make it so bloody complicated.
You could always machine the front of the manifold to accept a normal thermostat, at $15 each .

Regards Philip A

[Hardy]

Marty1 - what Phillip A says.

Thermostat is a round plastic housing with 4 inlets - when connected actually looks a lot like an artifical heart, similar price. No easy way of bypassing, not for testing anyway.

I'll get me a new one tomorrow, see what happens.

[peter r]

G`day Hardy , i guess you know 38s had problems with top hoses but would have thought it was rectified by your but maybe not .

I guess in your place i`d hope at the stat too but can`t really see how the bypass would affect it in this way .

Being what it is ( bore size ) and the fact that head gaskets and liners that leak into the cooling system create excessive pressure ( hose ) and it generally happens quickly under load , it may need a bit more looking at .

If it has any bubbles in it or if it looses coolant or the level rises and falls even at idle when unpressurised ( cap off ) these would be indicators .

Possibly if your plugs have done a bit of work they may tell you something , specially if 1 or more looks cleaner than the rest .
If it is combustion pressure into the coolant system the coolant generally leaks back into the cylinders when it is shut down and then is present when it is started and will give a steam cleaning effect in the leaking cylinders .

Good luck and hope it is something odd and simple , our 85 has a 4.0ltr bottom so will read with interest also partly because the more i learn about them the less i like the engineers that built them .

Peter .

[Philip A]

It might only be the hose of course.
Apparently Rover had 9 designs for the top hose after the numerous failures caused overheating.
Why not put a new hose on and see. Hose is probably only $40-50 you are risking.
Regards Philip A

[peter r]

G`day Hardy , thinking about it today and it may be odd and simple .

The pressure release valve isn`t working , it should release the pressure before the hose is able to balloon as it has .

I`m not familiar with the set up on yours on a usual set up it would be the radiator cap , so if it has a cap on the overflow tank i suggest replace it and check that the pipe work to and from is clear .

Just the hose ballooning won`t affect the temp gauge .

Goodluck .

Peter .

[Hardy]

Well I think I may have sorted problem without actually knowing what caused it.
After mainly dicking around with thermostat, a radiator flush and system fully filled with water, evertyhing seems fine. Couldn't replicate problem - today was even hotter than before too.
So put a new hose on, filled with proper coolant following RAVE instructuions then went for a decent test drive - all cool.
Effen hose was $130 - LR part though. LR dealer wanted $218!!

So for future reference's sake of the forum, here's what I do know.

1. Expansion tank was basically empty. Old coolant evident on underside of starter motor.
2. Bit of crud fell into bucket when I pulled last pipe off thermostat.
3. I pulled top hose off 2 weeks ago (300k's ago) to fit new idler pulley, just stuck hose back on. Didn't consider bleed hose to exp tank.
4. Thermostat worked fine during 'bench' test

So there, dunno.
I know my car did have some new hose fitted during a recall, but that happened before I owned it.

Thanks for all your help fellas, t'was inspirational.

Hardy

[Philip A]

The problem with the recalled hose was that they got airlocks on refill, as they were higher than the Rad tank.
Thats what probably happened to yours. Maybe point it up a steep hill next time you fill it.
Regards Philip A