P

p38swansea

Member
Picked up a cheap 4.6 P38 a fortnight ago which needed new head gaskets. Had them done by a local garage, also had a new radiator. Picked up up on monday, and it's been running well. Survived a trip from Swansea to Newport and back without any issues.
However, today after I drove it for a few minutes the temp needle shot up into the red. I also noticed before I set off that it was idling a bit rougher.
Left it to cool for a few hours, but the same thing happened when I tried to drive it back home.
Any suggestions what the problem could be?
Thermostat is also currently disconnected and bypassed.
Hoping I didn't boil the heads, as I had to drive for a short while with the needle in the red to find a safe place to pullover.
All suggestions appreciated.
 
bad luck old bean, were the cylinder liners checked for movement before they did the heads.. There's plenty of info regarding the liners causing foul play!!
 
Bleeding the Rover V8 can be a bit of a pig, check for airlocks too.

A coolant sniff test using block testing fluid couldn't hurt either.

The stat on these things is a multi-port plastic thingy on the bottom of the rad hose, bypassing it mus have been fun!
 
Heads were skimmed and pressure tested hot & cold prior to new gaskets
Mechanic said liners were perfect and hadn't moved at all
 
After mine blew the top hose, I had rare fun (NOT) bleeding the damn thing :mad:

I topped it up with OAT (red/orange) coolant, let it run up to speed, revved it, drove it round the block and the cold air needle in red started so I left it to go cold (overnight in my case).

Topped it up some more, same again.

Day 3, topped it up, ran it hard uphill and let it cool. Topped a litre in the coolant and it's been mint ever since. Survived a 140 mile trip so must be bled now :p

There are various ways to bleed them, but I had time on my hands, so just kept letting it cool & top it up. Whole system holds around 11 litres.
 
If the ECU 'thinks' the engine is overhot it will adjust fueling to match....this can cause rough running.....
 
I've always bled mine by the (RAVE) book, and never had a problem with airlocks in the system.
Disconnect the radiator bleed hose from top of rad and blow through it to make sure it's clear of liquid.
Fill the reservoir, start the engine and let it idle, keep topping up the reservoir as the level of coolant drops. Let the engine get to operating temperature so the thermostat opens (top hose gets hot). Switch off engine, allow to cool, top up reservoir, replace reservoir cap.
I'm not sure what difference having no thermostat fitted would have on this procedure. If you're worried about air-locks squeezing the top hose to pump coolant round the system apparently works, but you shouldn't strictly have to do it.
 
Filled up the coolant today into the radiator top hose, took another 2 litres before it was full so I'm suspecting a leak somewhere.
Blew through the bleed hose and it was clear.
Anyway, drove it around for about 5 minutes before it overheated again.
Went to fill it up again, and it took another 2.5 litres! Not sure how it could have lost so much in so little time.
Braking also seems to bring down the temperature needle, so there's definitely an air lock somewhere in there.
I can't see any obvious leaks so I'll be leaving it with the garage in the morning to see if they get to the bottom of it.
Hopefully they'll bleed it properly to stop air locks too.
 
Check all your hose connections when I swapped out my rad and water pump one of the clips wasn't as tight as it should have been so when left standing it would weep a lot over night because the system is under pressure, does that make sense ???
 
Was the block pressure tested when the heads were checked ? Could be core plugs leaking, or a hidden internal crack, even if the liners are ok. If there's any leaks allowing the system to de-pressurise when hot, it will overheat. Pressure is required to reduce water boiling.

Also, how is the thermostat bypassed ?? It has three connections, so not as simple as other cars. Initially the coolant circulates through the heater, and then through the radiator after the stat opens. . . . . .. or did they make a special three-way bypass system ?
 
pwood999 said:
Was the block pressure tested when the heads were checked ? Could be core plugs leaking, or a hidden internal crack, even if the liners are ok. If there's any leaks allowing the system to de-pressurise when hot, it will overheat. Pressure is required to reduce water boiling.

Also, how is the thermostat bypassed ?? It has three connections, so not as simple as other cars. Initially the coolant circulates through the heater, and then through the radiator after the stat opens. . . . . .. or did they make a special three-way bypass system ?
Click to expand...
That was my query above - bypassing or removing the stat is not simple on the P38 due to its design.

Also, it may pay to get a static pressure check done for leaks.....pressure testing kits can be hand for relatively cheap on ebay/Amazon these days!
 
Heads were pressure tested hot & cold and were fine.
I'm not getting it back until Monday so I'll have a look then to see how the stat is bypassed
 
Might be worth chucking some UV dye in the water tank and then checking if it turns up anywhere it shouldn't.
 
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