ZT 160 KV6 coolant problem
 

Hi, I have a problem with the cooling system in my 160 KV6. The expansion tank has started to discharge coolant when hot. The heater is blowing hot but the radiator is cold and the pipe from the thermostat to the rad (the one with the bleed screw) is cold. Radiator fan is also running high but not helping matters because there is no heat in the radiator.

The thermostat and water pump were replaced in January but the problem has only just started. When I open the bleed screw water come out and the hose begins to get warm, between the thermostat and the bleed screw.

Is it likely an air lock has developed? Could there be a blockage in the radiator?
Scratching my head at the moment.

Point to note, when all was running well, the heater worked but not as hot as it is now. It suggests it is getting to hot on that side of the system, hence the discharge from the expansion tank.

Help would be much appreciated.

Hello David and :welcome: to the club.

As you say, the first thing to check is that the system has been bled of air properly. Before we go any further, are you DIY-minded or are you relying on garages?

Simon

I am doing all the work myself. So far (since Christmas): timing belts, ancillary belt, water pump, thermostat, gold resistor upgrade, new trinary switch, VIS motors, etc, etc,.
I wonder if there is a blockage in the radiator as this problem has just started recently, and the system was fine after the above work. Just started doing this problem.

I did read somewhere that someone experienced a similar problem (cold radiator) and found the small pipe from the rad to the expansion tank was blocked. Fine once cleared.

Here is the official KV6 bleeding procedure.
I recommend that you begin by draining the system fully not forgetting the cylinder block drain plug. It's important to raise the expansion tank as instructed and don't start the engine when the bleed screw is removed.

Is this car a recent purchase? If so, could the previous owner or a garage have put K-seal in it?

Simon

I got the car in December. It did this once before, just before I drained down to do all the work. After the refill it was fine for a while and the on Sunday it overflowed. I have even taken it round a track, back in February. I gave it lots of revs and completed several laps without any problems. Now I have the problem. It points to a blockage somewhere.
What do you think?

We've heard this story before David. These are the classic symptoms of a thermostat which isn't opening. It happens after K-seal or Steel Seal has been put into the cooling system and interferes with the thermostat's operation. It causes unpredictable and varying behaviour just as you describe.

You mention the possibility of a "blockage" in the radiator. I'm not sure where material would come from that is capable of blocking every channel. When you drained the coolant, was it heavily contaminated? You've said that the heater is blowing hot so how is it that the radiator could be blocked but the heater matrix isn't?

Some members have found a lump of sealant in the flow through the oil cooler. That would produce your symptoms but I suggest that you start with the easiest test: a full drain, refill and bleed. You can back flush the radiator then to settle the question once and for all.

Simon

Thanks Simon, I will try a full flush. The coolant that came out when I drained did not seem contaminated. However, I would describe the problem as unpredictable so you could be right about K-seal. Although I did replace the thermostat at the time. I will have a play at the weekend and report back.

Quick update: I removed the small breather pipe from the radiator to the expansion tank. It was clear. Air line on the expansion tank connection to clear that. Using a small funnel inserted into the small vent pipe, now reconnected to the radiator but not the expansion tank, I slowly added coolant to the system through the funnel until the level in the expansion tank started to rise just above the ribbed section. Started the engine and left running until warm and the radiator started to get warm.
So, thermostat clearly working and air lock now out (so far).
Removed the expansion tank cap in the morning and there was a wush noise, indication the system remained pressurised over night.
I then took the car for a nice drive to the coast and back (100 miles). All good!
Let's hope the fix is permanent.

If that's the case then the valve in the expansion tank cap, designed to prevent the creation of a vacuum, isn't working.

Simon