K Series Cooling Issues

[Dave_P]

Can any one help. Have a standard 115hp 1600 k series on a 2002 plate. Under normal steady driving conditions the engine temp is on the mark at around 80deg. When driven at 60 -70mph the temp drops to 60 deg and below. This happens in the length of time for a lap at Curburough, I think this is low for high reving. But driving in traffic, stop starting, the temp climbs quickly to 100 plus. The fan cuts in at the correct point but at best holds the temp, does not reduce and is only remedied when I start moving steady. When I first got the 7 It took an age to warm up and in the winter only just reached temp even on long jaunts.I replaced the coolant and found the thermostat missing. I replaced this so should be as designed. I feel I have been lucky so far not to have an overheat in traffic. Not a mechanical newby but don't understand what can be happening. Newish owner though. Any suggestions desperately recieved. The good weather is here.

[SM25T]

Have you got a heater ? Could be an airlock in the heater after you fitted the thermostat ? Are the hoses the same temperature each side of he heater ?

[Dave_P]

Yes heater. Yes hoses same temp and heater works. I filled system as usual then topped off through top  heater hose and used a syringe to top off the heater. Then quickly reassembled. The coolant level in the header remains constant. I have done all the hose squeezing exercises too. I now have a grip like Garth.

[Ian B]

Have you drilled a 2mm hole in the top of the thermostat flange?

Without this is can cause irregular airlocks.

[Dave_P]

I purchased the thermostat from Caterham to ensure correct opening for type. It had had hole in it which I made sure was uppermost. If the only issue was the overheat, We might get to the bottom of it. But the overcooling when working hard and fast is really odd. By the way, thanks to all for advice given so far 

[revilla]

What kind of radiator do you have? I know somebody who had a similar pattern of problems when he fitted the triple pass race radiator, all cured by going back to a standard rad. At idle in traffic it seemed that the water pump just couldn't drive enough flow through the increased resistance of the radiator. Quite how it led to overcooling to well below the thermostat temperature is still a puzzle!

Although the hole in the stat is primarily there to allow airlocks to escape it had another beneficial effect in that it allows a small flow through the radiator when the thermostat is closed which prevents the water in the radiator stagnating and becoming over chilled. Without this you can get a thermal cycling where the thermostat closes, the water then circulating through the bypass hose slowly heats up but the water stuck in radiator goes cold. Once the bypass flow is hot enough to open the stat you then get a sudden inrush of cold water from the radiator, the temperature of the water leaving the head around the bypass drops dramatically so the thermostat slams shut and the whole thing repeats, with the temperature cycling up and down and spending a lot of its time well below the thermostat temperature. It's a consequence log the strange cooling arrangement on the K Series with the thermostat in the radiator return rather than feed, relying on the bypass circuit to control it.

I just wonder if, with a bigger radiator you still get excessive chilling of the water it contains when the thermostat is closed, beyond what can be overcome by the small flow through the hole in the stat, leading to the same thermal cycling?

[john milner]

The previous owner had removed the thermostat for a reason. Which was probably to keep the engine a bit cooler for track use but could it have been to overcome a dodgy pump? It may be worth checking that the rest of the plumbing is standard.

[Ivaan]

Sounds like you need to fit a PRRT Thermostat.

Once fitted, ( and it's an easy job ), the temp will stay constant and you'll not have airlock problems.

They're fitted to K Series Landrover Freelanders. There are two versions - different temperatures - If you do a tech search you should find the details.

[Dave_P]

Many thanks to all. Revilla, Standard caterham radiator fitted, aluminium 40mm thick at core.

John, thorough inspection would indicate all is as Caterham standard.( Is that an oxymoron?)Going to presume pump is ok as I have no way to check pressures. But coolant squirts back to header as in my Astra.

Although I am sure there is no air in the system,going to roll out onto steep drive then jack up the front to be sure. If no change will be fitting PRRT thermostat bit pricey but consensus seems to point to this being the surest way (most of the time). Do we agree that the lower temp stat 82-84 deg instead of 88 will be the safest bet. Will post results when done. By the way have you noticed that no matter how careful you are the garage floor takes on a pink hew when you have had the 7 cooling in bits a few times.

[john milner]

To summarise: High revs = overcooling, low revs =undercooling. Assuming the pump is okay the flow rate is dependent on revs. The fan has little effect on coolant temperature. 

Could the thermostat be faulty or installed the wrong way around? It could be that it is opening and closing too late.

My gauge is rarely far from 80 and has no aftermarket/customised plumbing or stat drilled hole. My fan lowers the temperature very quickly. My thinking is that 82 is best.

[Jonathan Kay]

As above.

1. Try a bit more jacking and Garthing, as planned.
2. Check which way the fan is blowing, and if those haven't improved anything:
3. Remove and test thermostat (or try another).

Jonathan

[glasgow]

I am not sure if this is related but my engine started overcooling on rev after I did the coolant hoses bypass modification. Is your coolant circle the original or the modified?

 

Ahmed

[Dave_P]

thanks for that. standard layout

[jonheli]

Don't know if this will help - Mine has a brass bleed fitted into heater hose; once jacked up, you remove a screw on cap and then fill via the expansion tank until coolant appears in top radiator plug,Replace plug in radiator and screw cap on, then top up expansion tank after letting car back down. Usual hose squeezing, then recheck level.

[charlie_pank]

Are you sure your coolant sensor is telling the truth - can you take it out and test it in a pan of water with a thermometer?

If it IS telling the truth then I can only conclude you have an airlock somewhere (your having tried really hard to eliminate any airlocks is not *proof* that there aren't any, it might just be a really stubborn one). You could therefore try the only method that I could employ to fill my (non-K) engine when it had been completely dried out:

 

1. Suspend header tank from ceiling, as high as possible

2. Open header tank cap

3. Run engine for a couple of mins (with heater valve open)

4. Wait

5. Top up

6. Go to 3 until no more bubbles appear in header tank

7. You can then run the engine up to temp without the cap on (note that you shouldn't make a habit of this as it has the effect of running the system de-pressurised, thus decreasing the boiling point) Look out for big glugs firing hot coolant out of the header tank - perhaps leave the lid on a bit. Top up as bubbles appear, continue until no more bubbles.

8. Let the whole system cool down overnight

9. Repeat.

 

 

[glasgow]

Didn't realise the heater t bleed can come in brass. Is this better than the plastic?

[Jonathan Kay]

Yes, some plastic ones have cracked. There's a spec in the archives.

Jonathan

PS: Annual event, Ahmed? :-)

[glasgow]

PS: Annual event, Ahmed? :-)

Haha, thank you Jonathan. Totally forgot about it. 

But I wonder why they don't come in metal instead of the fragile plastic

[pensioner]

If its any help I have spent weeks and ££ trying to sort my k 1.8 temperature problems, Thermostat, sender, new hoses and finally resolved with a new expansion bottle top.

at £8 it was a cheap fix

 

[Smithy77]

What kind of radiator do you have? I know somebody who had a similar pattern of problems when he fitted the triple pass race radiator, all cured by going back to a standard rad. At idle in traffic it seemed that the water pump just couldn't drive enough flow through the increased resistance of the radiator. Quite how it led to overcooling to well below the thermostat temperature is still a puzzle! - See more at: http://www.lotus7.club/forum/techtalk/k-series-cooling-issues#sthash.cpDjMHmm.dpuf

Yes, that was my last car which cam with the triple core jobbie. A single core rad didn't completely cure it, just made it much less extreme and managable to a degree; it still over cooled with ambient temps below 10C. Strangely enough, I have experienced exactly the same symptoms with my new 230bhp K series, but this has a standard 40mm single core ali radiator 

[AndyCam]

This all sounds familiar.

As mentioned in multiple threads, airlocks cause symptoms of overheating and the bottom hose doesn't get warm. The methods above will work, but also I'd also suggest blowing down the "jiggle" ball-value tube on the inlet manifold (insert drinking straw) just to double check its not crudded up. Do the same with its hose into the header.

As for the overcooling I'm running the stock rad on a 1.4k classic (plastic capped rad) and after flushing the rad and installing new stat & sender the temp would drop significantly when the car was driven hard. Appears that the rad is just too efficient now. Solution is blanking 1/3rd of the rad with cardboard. Hat tip to Chris at 7 Workshop for that. Happy all day at 80 now.

[Smithy77]

Radiator blanking was what I resorted to as well and did the job of maintain temps around 80C. If there is enough demand for them, maybe someone can run a production of clip-on aluminum blanking panels which would be quite a neat solution, then easily removed for hot / track days.

It remains a mystery how certain specs of K series engine don't suffer from over cooling on cold days. Revilla for example, with his fleet of VVC 160 engines, reports a steady 80-85c in all conditions and all air temps on all his engines. But then we have a 1.4K classic and a 230bhp K both over cooling!! There has to be an explanation....

[Jonathan Kay]

Titanium!

I don't understand it either, but there's enough out there, including mine, that clearly need it. It didn't before it was rebuilt and now it does... the only obvious difference being a lower temperature thermostat.

There's at least one Member who has the blanking remotely controlled from the cockpit...

Jonathan

[revilla]

Yes my engine seems run just over 80 in the gauge pretty much all the time. When stuck in traffic it creeps up slowly a little until the fan kicks in which brings it rapidly back down again. Suspect the true temperature allowing for gauge inaccuracies may be slightly higher as there isn't much of a visible rise on the gauge before the fan kicks in, so maybe in reality it's  5 degrees higher. Even driving at speed in temperatures close to freezing doesn't cause overcooling. This behaviour has been pretty much identical across three engines. Standard aluminium radiator and cooling circuit other than a 2mm hole drilled in the thermostat which made it a lot easier to fill and eliminated thermal cycling entirely.

What I would like to understand in this case is this; even the most effective radiator in the world shouldn't be able to cool the water much below the thermostat temperature as the thermostat should shut off the flow to the radiator leaving only the bypass circuit. It doesn't really make sense to say "may radiator is working too well" because the radiator should be cut off below thermostat temperature and should not therefore have anything to do with it at low temperatures. Any 2mm hole in the stat shouldn't allow enough flow to provide effective cooling.

So how are these engine temperatures being pulled so low in cold weather conditions? Why is there any need to blank off the radiator at all? Undoubtedly it does work for some people, but why? And why do they vary so much?

[Jonathan Kay]

Yes: those are the two fascinating questions.

Jonathan

PS: No bonus hole in my thermostat and the coolant does stay too cool.