1hz motor full coolant expansion tank - indicator of a problem in cooling system ? (1 Viewer)

[sunrk]

Been doing a bit of work and had engine bay open. Noticed a bit of coolant leaked out top of expansion tank. Went to lift it, and the tank is totally full!

I have not over-filled it when topping it up. I can certainly take it out and removed the excess so it back down to the right level.

I was driving it about 4 hrs ago but it's cooled down to about ambient now so excess coolant pushed out to the tank should have been drawn back to the radiator. I took the rad cap off and there was just a tiny bit of pressure. The top of the radiator is not filled right to the top but is fully covering the core.

When I drove the work on a hot day recently the temp got up to 86 C but the temp came down again back to 75 to 78 where it's meant to be.

Could it be a sign that the t-stat is not working correctly? Or that something is blocked up? What controls the backflow of coolant as the motor cools down?

Motor is about 7000 km off needing the t-belt and tensioner (and water pump) done again at 700 k km's. I do the t-stat as part of the job.

It's a 1hz non-turbo'd motor.

Thanks.

 

[BILT4ME]

The top coolant tank is supposed to be full. There should be no air in it. The overflow tank should be what is varying in level.

If this continues, it's probably your radiator cap not functioning.

 

[sunrk]

Sorry that is what I meant - the overflow tank is full and the excess coolant didn't get drawn back into the radiator to fill the top tank. I'll get a new rad cap ASAP then and try that.

 

[mudgudgeon]

Agreed, likely a bad radiator cap.
They have a two way valve in them. Lets excess pressure out, and should allow it to draw back coolant as it cools down.
If the drain back valve isn't working, you can end up with a full overflow and low level in the radiator

 

[BILT4ME]

Sorry that is what I meant - the overflow tank is full and the excess coolant didn't get drawn back into the radiator to fill the top tank. I'll get a new rad cap ASAP then and try that.

If you have a leak in the system such as a pinhole in a hose or a leaking o-ring, then it may not draw the coolant back in because it takes the path of least resistance. Change the cap, but you also need to look at a cooling system pressure testing kit to locate any other problems.

 

[sunrk]

Got a replacement rad cap - Tridon CB-1390 is the right aftermarket one. A$18 from Repco.

Have not been for a big drive but just got the 80 passed for rego and while there with the motor at almost normal temp I checked the overflow tank and seems good. I took the existing (OEM) rad cap off this morning to pour coolant back in to top tank of rad and did notice the cap seems to bind a bit.

Got a couple of drives to/from work this week so we'll see what happens with the replacement cap fited.

I do check the hose clamps and connections fairly often but found one at the heater tap weeping a little.

 

[sunrk]

Ok, so replacement (aftermarket - Tridon brand) cap has been on a few days now, and the cooling system is working properly. So I think it's fair to say the radiator cap (OEM) was the problem. Will try to source a new OEM cap (the later p/n) and keep as a spare.

I don't rule out that there could still be an issue elsewhere such as leaks I don't know about (apart from the heater tap hose one I'm fixing up hopefully today). I've never had the head off the motor in the time I've owned the 80 (coming up on 12 yrs). But the radiator was new OEM fitted 4 yrs ago, and the water pump and t-stat were both new OEM at last t-belt change some 93 k km's ago.

 

[BILT4ME]

Ok, so replacement (aftermarket - Tridon brand) cap has been on a few days now, and the cooling system is working properly. So I think it's fair to say the radiator cap (OEM) was the problem. Will try to source a new OEM cap (the later p/n) and keep as a spare.

I don't rule out that there could still be an issue elsewhere such as leaks I don't know about (apart from the heater tap hose one I'm fixing up hopefully today). I've never had the head off the motor in the time I've owned the 80 (coming up on 12 yrs). But the radiator was new OEM fitted 4 yrs ago, and the water pump and t-stat were both new OEM at last t-belt change some 93 k km's ago.

Do you have an OEM radiator?

I have read about OEM caps having an issue when installing on an aftermarket radiator. In this case, the aftermarket cap may work better if you have an aftermarket radiator.

Either way, I hope the issue is solved long term.

 

[sunrk]

Yes a genuine OEM radiator installed about 4 yrs ago. Replaced the original genuine OEM radiator installed at the factory in 1992.

 

[BILT4ME]

Yes a genuine OEM radiator installed about 4 yrs ago. Replaced the original genuine OEM radiator installed at the factory in 1992.

I had a radiator explode partly because the cap had so much gunk on it, it couldn't open and relieve the pressure when needed. That was an OEM cap.

 

[DivByZero]

Radiator caps are an often overlooked service item. They should be considered a consumable and replaced at intervals. They're a critical moving part of your coolant system, so just like water pumps and thermostats, they should be replaced as preventative maintenance. I change mine out every 5 years or 100,000km. This is born from experience. I cooked the engine on a Mitsubishi Magna 15 years ago from a failed radiator cap. Expensive lesson for such an easily replaceable cheap part.

 

[DivByZero]

Oh, just to scare you, air getting into the coolant system was the only sign I had of a cracked head on my HZJ80, but that's unlikely to be the issue here.