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Strange behaviour when hot (P4)

1K views 18 replies 7 participants last post by  armoore 
#1 ·
Hi Guys,

Been having problems with the permanent 4 (1991 without cat) after being in traffic for a while when the engine gets warm/hot with coolant reading 95 c. You go to put your foot down and there is a strange lack of power and a sort of tappety noise. After a minute at higher speeds it cools off a bit and starts behaving again.

Any ideas? Rest of the time it drives great.
 
#3 ·
Well I didn't find any boxer engine to like been hot..... :mad:
Every summer I hate to drive in traffic..anything hoter then 75c means too hot for boxer..
And yes my fan starts too at 85-88c... So I really think 95c is too high..So check your temp sender for fan..its mounted on the radiator.. on left side when you look from inside of the cabin.. And as far I searched net for more info it's always only one solution ,best full synthetic oil 10w-60.. But again I'm using only Agip (Sinth2000) 10-40 and I'll stick with it..
I guess it's the price we all pay to live with boxer... :rant:
But my boxer loves mild cold weather....10-15c and all of the cold air getting trough K&N... :cheese:
 
#5 ·
Could it be that the hydraulic tappets are losing their oil and thus giving the valves low lift until they are pumped up, again hence the tappety noise and lack of power. On my 33 I fitted a by-pass switch in parallel to the activating thermal switch so that when the temperature starts to rise I can switch on the cooling fan. ;)
 
#6 ·
Do you have an induction kit? They suck hot air from under the bonnet unless you route a cold air feed to them. At high temp or if you've been sitting in traffic, the cool air just isn't there for a few seconds, so it'll be sluggish.

Ralf S.
 
#7 ·
No, it doesn't have an induction kit. armoore, please excuse my ignorance - if the tappets were losing oil how would I know...would this be something that happened when the engine/oil gets too hot? Maybe I should try an oil change.

That switch idea sounds good.
 
#8 ·
bw said:
No, it doesn't have an induction kit. armoore, please excuse my ignorance - if the tappets were losing oil how would I know...would this be something that happened when the engine/oil gets too hot? Maybe I should try an oil change.

That switch idea sounds good.
Oil becoming too viscous at high temp.
Can you try a higher grade oil?
 
#12 ·
bw said:
5w 40 fully synthetic, think the brand is Carlube - just el cheapo brand
thats about the same I've been using on my 33 16v... BP Visco 5000 5w40 fully synthetic... and have had no problems yett (knock wood... ;) )
 
#13 ·
i found out the hard way that 5240 was too thin for my p4.
the oil gets hot and very thin and then it cant drive the valves properly. it doesnt do the pump any good and if you drive your car hard you can pop some of the valves! then you need new ones! thats what happened to mine.

move up to 10w40 or even 15 if you car is running hot. get a lower temp thermo for the fan. around 80deg c should do the trick. if you car still having problems maybe you could fit an oil cooler. i had one on my p4 and it made all teh diffrence! thrash it all day long and the temps stayed down.

good luck.

L.
 
#15 ·
The hydraulic tappets work by filling with oil and they are designed to gently leak/bypass some of it only for it to be replaced by the lubrication system (I have a fuller and more accurate explanation if required!), however at idle, and when hot the oil will become less viscous (more runny) and perhaps lose too much oil. then as you use some revs the tappets will pump up again but will briefly have too much clearance and hence the noise initially. I run my 33 and BMW R100RS with oil temperature and pressure gauges so that I can keep an eye on them (t's and p's). I run my 33 on 10W 40 winter and 10W 60 summer. :)
 
#16 ·
Just seen the reply stating use of oil cooler - good idea, did you know that the Citroen 2CV had an oil cooler so that the valves were fed a nice cool charge of oil. I've seen many 2CVs thrashed in France over the years (had one once) and the only way to get around in them is at full revs and not to lose too much speed in the bends, they roll horrendously but manage somehow!
 
#18 ·
armoore said:
Just seen the reply stating use of oil cooler - good idea, did you know that the Citroen 2CV had an oil cooler so that the valves were fed a nice cool charge of oil. I've seen many 2CVs thrashed in France over the years (had one once) and the only way to get around in them is at full revs and not to lose too much speed in the bends, they roll horrendously but manage somehow!
Did you hear of the 2CV challenge... It's where drivers do whatever they can to topple a standard 2CV on a race-track. Apparently it's only been done once!
 
#19 ·
bw said:
armoore - is it much work installing an oil pressure gauge? I'm quite surprised the P4 doesn't have one as standard really.
No not really. The take off point for the temp gauge is at the rear of the crank-case where the oil warning light switch goes, this can be retained if an adapter is used. The pressure take off is just by the oil filter. I used electric gauges mounted on that slot (blanked off and holes drilled) below the heater controls/ash tray) so not too easy to see but O/K. There are plenty of power sources for the electrics/lights behind the plastic. TIM gauges are o/k but the variable resistor in the pressure sensor can get dirty causing fluctuations but I picked up some for £2 (including gauges!) at an AROC national day. ;)
 
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