General knowledge engine question.
 

Ok, I realise this is not Cobra related but there is a fair bit of knowledge in here so I thought I would ask.

My wifes car (1994 Ford Capri, twin cam, non turbo) has had an on going problem for a couple of months now.

When driving at 60 kph the car is fine, all ok
But get upto 80 or more and the temperature creeps up, it will go all the way to hot if you keep going at speed.
Before Christmas it developed a coolant leak in the bypass air solenoid (this allows crankcase fumes to be drawn into the intake manifold once the car is upto temperature) I replaced this with a decent second hand one (new is no longer available) I reassembled the car but discovered further coolant leaks in both the water pump and the radiator (no inhibitor), so I replaced both.
Now I am not 100% sure if the problem started at this point or was ongoing from when it had coolant leaks.
I then replaced the thermostat and the radiator cap. Still no good.
I then checked camhaft timing (as timing belt is removed to replace water pump - I also replaced the belt while I was in there) and the timming was fine.
Next I thought it may be a faulty solenoid I initially replaced, so I clamped off the air hose, still no good.
I was then scratching my head as it did not present itself as a head gasket issue, but thought that there is nothing else left.
So 3 weeks ago I pulled the head (could not see evidence of head gasket failure, nor a running lean or burnt valve issue), sent it to a machine shop for pressure testing, resurface and replace valve stem seals ( I do not have a valve spring compressor)
Well after being promised I would have the head by the following Friday, it ended up taking him 3 weeks (he lost a valve collet), I got the head back this morning, I cleaned everything and refitted it, only to have the same fault still occuring.
Really clutching at straws now I thought that maybe the new thermostat is faulty, so I cut the centre out of my old one and fitted it, still doing exactly the same thing.
The water pump appears to be flowing correctly, as I can see the water passing over the radiator tanks inside fairly quickly with thermostat removed.

And that is where I am at now, so does anyone have any ideas?

I think the radiator is plugged.

Does it have electric fan(s) and is it working ????

Winner, winner! Remove it and send it to the radiator shop to check out the flow. Not completely plugged, but clogged just enough to inhibit full flow when it is needed the most.

Electric fans really only are there to keep thngs cool when the car isn't moving.....although they can cause the described problem if they are wired backward!

Had a mate with a similar problem...302 Cobra getting hot and cooling very slowly. Checked everything couldn't find any problems. Whilst talking at my place about fans etc I pulled the one for my cobra out of the box and hooked it to a battery. He straight away said "Sheet my fan doesn't blow that hard" Turned out he'd bought a brand new lemon that ran at about 1/2 it's proper speed.

Hey David,
Have you ooked at the radiator hoses, maybe the feed from the rad to the pump is sucking closed,starving the pump with water at speed.


Phil

Hi Pat, the radiator is new, but I will pull it out and see if I can get the flow checked.
RustyBob, the fans are working correctly and are blowing in teh correct direction.
Rob, If it was a fan issue, as Pat says it would not happen when drivin(as road speed would give air flow better than any fans).
I will also check for anything blocking the airflow, and just last night realised that I have not refitted one of teh undervehicle (under engine bay) shields, so this might be having an effect on air flow and air direction.

Thanks for the ideas and tips, please keep them flowing and I will let everyone know what I eventually find.

Hi there Phil, the radiator hoses where replaced at same time as the radiator, so there is a chance this could be it, will check within the hour.

I'd be leaning that way too. I had a Rod that looked fine in the top of the radiator, and I did everything ELSE to correct the problem. Since the radiator was the only thing left (pressure tested system to make sure there were no unseen leakage) I finally replaced it. I removed the side tanks for my own edification and there was at least a third and closer to a half of the lower section on both sides that was full of sediment from all the years. It would idle indefinetly without overheating, worked fine at lower speeds and around town, which is why I initially passed on it being the radiator, but once you started over the highway the temps would gradually increase to overheat. Problem disappeared immediately after. I really couldn't believe the crap in it, probably from a poor water source at some point( maybe several) over time.

That's also a good possibilty seeing that he already replaced the radiator( didn't see that before I last posted). It's not uncommon for the spring that is in many to fall out or removed when radiator or other work involving the hoses is done.

sounds like airflow. Also just check (a long shot I know) that when the bonnet is closed it is not pressing on any hoses. Saw this happen to a car on a dyno, it was good as gold on the dyno with the bonnet up, bonnet closed and it went all weird - turned out the bonnet was "just" touching an aftermarket fuel pressure reg.

There's your problem Ford crapi's were never designed to be driven fast.....

my money is on the radiator.

Ok, I have been out there chasing my tail again.
I thought I was onto a winner with the radiator hose sucking in, tested this first thging this morning, started teh car and revved to 4000rpm, no problem revved a little higher and it started to suck in. Then thought I better try it when engine is upto temp and cooling system is pressureised, well it did not happen once warmed up, and when driving it never gets revved that high.
100kph is about 3200rpm, and the does not suck in till close to 6000rpm.
So I checked for air flow, could see no blockages anywhere, and I refitted the under vehicle shields and splash trays and refitted a new thermostat, drove again, still no good.
So I am now pulling out the brand new radiator, as I am confident that the water pump is moving the water fast enough (as evidence by the fact that the water cavitated and sucked the radiator hose in).
Will get the tanks pulled of at local radiator shop and see what is in there.

Even though it is new, there are too many things pointing at it being the fault.

If it has closed cores not due to foreign material there is going to be a very cranky phone call to Adrad.

Temp sender and gauge are both OK?

Hey there Merv, gauges are reading correct, have tested with auxilarry temp gauge fitted.

The`radiator is now out and going to be taken to radiator shop tomorrow, I still have teh original radiator (replaced due to split in top tank) and can see that the original has much larger tubes than the replacement, so it may be that the new one simply does not flow enough water.
Once again if that is the case there will be a cranky phone call to Adrad (they supplied with a 2 year no question asked warranty)

Good luck with that then dave. This has been a long and expensive process for you. I was more thinking about swapping the sensor.

Know a good mechanic Dave? :D

Only one I know at the moment is having his head done in by a bloody car.

Dave, I had a 6 cyl crossflow Cortina once that had the same issue as you describe. Temp fine under 110 k's but sit on more than that and temp crept up.

I never solved the problem untill the block was caustic dipped when I had it out for a work over.
Bit difficult with an alloy head to flush it with caustic. Maybe there is another good product available for flushing iron blocks without harming the alloy bits.