A friends N reg Rover 416SLi Auto has started to have overheating problems.
I understand this is a Honda engine in the auto version of the 416.
The details I have to date are:
It is not happening all the time but this may be due to shortish trip useage.
The stat was replaced. A pressure test found no problem.
On the most recent journey - 1st 40 miles on fast dual carriageway/ motorway at 60/70 it started to overheat.
Some minor loss of coolant so stopped and a minor top up of coolant
Next part - fast A roads probably similar speeds and another overheating situation.
Final part - fast A road at a controlled 50 mph with me in convoy appeared OK.
I have now changed the rad cap and checked the coolant level.
Heater is on , there appears to be no airlock but the bleed screw not undone as I do not want to risk disturbing anything else before it returns to base.
The rad looks good and no drips or puddles to be found from leaks
The return trip is planned to be a steady 50mph to see what happens.
A good local motor factor tells me they are supplying replacement waterpumps due to impeller failure.
Either the vanes have corroded away or have worn away.
If it is the pump what is involved in changing it and approx cost ?
Any other possible causes ?
Sorry I have no more details to date.
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Don't rule out a blocked radiator or sticking thermostat either.
When the engine overheats, pull over and (carefully) have a feel of the radiator. Is it hot, and if so is it uniformly hot across the whole surface? Is the hose from the thermostat housing piping hot as well?
I had insane problems of this nature with our Fiesta not long after I bought it and in this case, the rad was cold with the temperature gauge sitting up near the red. It would idle all day long without overheating, and if driven gently was fine, but would quickly overheat if worked remotely hard.
In my case it was a blocked heater valve shutting off the coolant flow when the heater was turned off, but a duff thermostat would do the same thing. This sounds like a circulation fault.
It could of course also be the pump, but this is a nice simple check to make first.
Cheers
DP
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DP Thanks for such a quick reply outside "normal hours"
Don't rule out a blocked radiator or sticking thermostat either.
It does have a new stat but of course it too might be faulty.
When the engine overheats pull over and (carefully) have a feel of the radiator. Is it hot and if so is it uniformly hot across the whole surface? Is the hose from the thermostat housing piping hot as well?
The rad certainly gets very hot. The driver slowly released the (tiny) cap carefully but in the release of hot water/steam the rad cap disappeared.
I went out on a rescue mission and found the cap in the main fan housing.
By that time, about an hour after it was parked, it had cooled but did not need much to top it up.
I will get the radiator temp checks done on the completion of the return trip.
>>In my case it was a blocked heater valve shutting off the coolant flow when the heater was turned off but a duff thermostat would do the same thing.
This sounds like a circulation fault.
I would agree. Hence the water pump suggestion seems to fit ( after eliminating the simpler things)
>>
On the first two legs of the trip the heater was OFF. On the third leg the heater was full ON.
At present the heater valve is manually operated cos the cable is bust plus the driver was lightly toasted on a warm day with no A/C [ ;-o
It could of course also be the pump but this is a nice simple check to make first.
>>
I am reluctant to touch too much due to it being 100 miles from home.
There is at least a mechanically minded person at its home.
Unfortunately it was an emergency trip so the full investigation had not been completed.
I do not wnt to disturb things at this end but a plan of action is most helpful
I will update what happens unless they decide to trade in this faithful Rover as it also has a few other lived with minor faults.
Thanks again
t
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If your waterpump impeller was that bad you wouldn't get the flow of water through the heater. If you run the heater on full heat full speed & it reduces the temp the chances are that the rad is blocked internally. is the fan comming on ? & if so are you getting luke warm air from behind it? if so suspect radIf the air is very hot & plentifull it iliminates the rad & pump
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IIRC this vehicle has a cooling fan fitted to the radiator. It may be this that has failed. Try bridging the sensor wires at the sensor pick up (may be to the side of the radiator) to see if the fan is turning. You could also run the can static to see if the cooling fan cuts in which will elliminate sensor and fan.
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These are the views of Robin the Technician with 35 years in the trade. I fix, therefore I am...
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Blocked rad is common on these and normally caused by coolant/anti freeze not being changed on time.
My Rover does this, but as I`m about to scrap it, I am not getting the rad replaced
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Steve
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Thanks for all the suggestions.
I have today had a chance to try out a few tests
Started with the header tank set at the correct level, a totally cold engine, bonnet up, heater on /heater fan off but with the car stationary.
I let is tick over for 25 mins,during which time I made the following observations.
1. soon after start - top hose warmed but bottom hose still cold.
2. 5/6mins later - tried the heater fan and it is blowing out lots of hot hot air ( assume Pump OK ?)
Top hose warmer but bottom hose still cold
Temp guage has moved into the lower part of its scale. Coolant in the header expansion tank has moved to half way betwen max mark and the top.
3. 15 mins from start - Rad now hot at the bottom ( where I can access to touch it)
Bottom hose now hot ( I assume the stat has opened ?)
4. 20 mins still no fan started
5. 25 mins still no fan started. All other indications the same.
6. 30 mins - after 5mins of 2500rpm the fan came on for a short time.
It started and ran at a good speed ( so the motor seems OK).
Is the heat sensor for the fan working correctly?
Temp guage no change. Bottom hose nice and hot. All other indications the same.
To recap previous situation.
New stat and rad cap
No leaks found and ( coolant?) pressure test was good.
( hoses do not appear to be impeding flow so no internal collapse ?)
Remaining popular suggestion is a blocked rad.
So go straight for a descaler or the garden hose to flush out the rad on/off the car ?
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A good and thorough test undertaken here - well done. From your observations, I would expect a car sitting on tickover that the cooling fan would have cut in well before the 25 mins mark - to have to rev it for 5 mins also seems excessive. It could be that the sensor has gone out of tolerance.
My suggestion would be to replace the sensor and whilst you have the water drained, give the rad a clean by reverse fush. It could also be that at some time someone has put a sealant in the system and this can contribute to the overheating.
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These are the views of Robin the Technician with 35 years in the trade. I fix, therefore I am...
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Thanks Robin. It is quite difficult to list the situations / actions from a keen DIYer
What you say makes sense I will pass the info on for action.
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It has survived OK, the non stop 100 mile return trip on fast A roads and Motorways.
Restricting it to 50mph and with the heater on full blast avoided the overheating.
Replacing the sensor in the radiator should allow using the rad fan rather than the heater fan to assist the cooling process.
The senario of the heater on full in mid summer is not very enticing :-)
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So far two different sensors have been offered by motor factors.
Unfortunately the Haynes manual the owner has does NOT cover the auto model ( and therefore not the Honda engine).
He has not been able to locate the sensor for the fan. We both thought it would be very east to find.
( one factor said it was by the thermostat but I suspect that is for the temp gauge)
Can anyone advice where it is ( and a part no ?), as Rover dealers are a little scarce these days.
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Give them the chassis no,that will sort it!
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Steve
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Give them the chassis no that will sort it!
Yes. Will do the obvious. I always think of VIN when visiting dealer spares dept but switched off when it was a smaller motor factor.
The sensor does seem to be by the stat but the one supplied to date has different connectors.
We are still making progress.
Next to try out is bridging this sensor connector to confirm activation of the fan
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A replacement sensor has been fitted and the radiator fan now cycles on and off much earlier.
I am confident that all is back to normal.
The next 100mile trip is on Tuesday so that should finally confirm "case closed."
Thanks to all from me and a happier good friend.
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whilst the fans may have been faulty they will do nothing to stop it overheating above 50 mph - the forced air flow through the rad is much greater than the fans have any effect on. If it is oveheating at above this speed then you have a water flow problem - either knackered pump or blocked rad as you have noted. Sorry, but I think you will still find it overheats if you give it some welly.....
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RichardW
Is it illogical? It must be Citroen....
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What about 'Air-Lock' in the system have you thought of this ?
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It sounds like the the sender was out of tolerance. Do let us know how the trip goes, as feedback is always vaued and welcome.
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These are the views of Robin the Technician with 35 years in the trade. I fix, therefore I am...
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OK, After the latests responses its back to the task.
A fast test run this morning did not provoke anything.
Next is a simple flush of the radiator ( cos it has other cooler pipes at the bottom -Gearbox or PAS ?)
Plan to use a rad flush additive and then refill.
Will investigate the bleed screw that is visible. It must be there for a good reason.
We have assumed that the pump ( wherever it is?) is working to some extent else the cabin heater would not get so darn hot.
I will report back on progress.
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Undoing the only bleed screw identified released coolant not air so unless there is another bleed screw it looks like there is the maximum coolant .
One additional piece of the jigsaw. When it started to overheat, the temp rose very quickly indeed. I would have expected a steady rise in temp.
The ram effect at speed was mentioned as sufficient to cool the radiator .
Quite a lot of the radiator is shielded by the bodywork so would not the fan suck a significant amount of air through the shrouded area to aid the cooling even a speed ?
The long test trip has been cancelled but a 20min blast provoked nothing nasty.
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IIRC an american discoverd the optimum air speed over a radiator for maximum cooling was 12 MPH. That's not vehicle speed. At higher speeds, the friction of the air generates enough heat to reduce the cooling effect.
I would therefore assume that if the air intake area was smaller than the radiator surface area, then the air flow speed over the radiator would be proportionately lower (and at higher pressure, but let's not go there. I'll let the aerodynamicicsts argue that one).
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Latest info.
The 100 mile long test trip appears to have been OK in both directions.
To recap, we did not "change just one thing at a time and check results" which in retrospect may not be the best approach
On closer examination of the NEW rad cap it appears to have a faulty seal and we think the coolant was not being sucked back from the header tank
The original rad cap was re-fitted before the 2 x 100 mile event free trips and so we are reasonably certain the new cap had introduced an interim problem.
So changing the stat ( condition unknown) and a temp sensor for the fan (definately faulty) we are hopeful the problem has been fixed.
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