P38 v8 Petrol Overheating

madbrit · Aug 8, 2021

My V8 p38 petrol 51 plate started overheating for no apparent reason, I had the block tested with the blue solution, no leak into cooling system detected, so I changed the pump, old one was ok changed the thermostat, changed the expansion cap, changed the Viscous unit, all to no effect, still overheating, so I thinking the new thermostat not working, so got old one, bodged it so water flows through anyway permanently, still overheating, I did get rid of any air locks by taking off the top hose, heaters are working.
I am now at a complete loss, any ideas anyone ? only thing I have not done is change the rad ;(

kermit_rr · Aug 8, 2021

Sounds like your radiator is blocked internally or externally then! It doesn't take much.
If you bodge your thermostat, then you will always have flow through the radiator and you'll never reach operating temperature

madbrit · Aug 8, 2021

yes that next is the next job Monday, pump water into the top, see what flow at the bottom, I presume that is the way, might just order another one anyway.

tomcat59alan · Aug 8, 2021

madbrit said:
yes that next is the next job Monday, pump water into the top, see what flow at the bottom, I presume that is the way, might just order another one anyway.

It may be blocked between the fins so take it off and have a proper look. There was someone a couple of weeks ago who thought their rad was clear until he took it off,a search (top right of page) may bring his post up.

discool · Aug 8, 2021

madbrit said:
My V8 p38 petrol 51 plate started overheating for no apparent reason, I had the block tested with the blue solution, no leak into cooling system detected, so I changed the pump, old one was ok changed the thermostat, changed the expansion cap, changed the Viscous unit, all to no effect, still overheating, so I thinking the new thermostat not working, so got old one, bodged it so water flows through anyway permanently, still overheating, I did get rid of any air locks by taking off the top hose, heaters are working.
I am now at a complete loss, any ideas anyone ? only thing I have not done is change the rad ;(

So what are the signs showing u have of the engine overheating?
The water pump doesn’t cause overheating unless the impeller has somehow detached , you hear that, thermostats can fail but usually open, the viscous unit is easy to test, the sound of it would give it away if faulty when starting up.
Was the coolant blowing from the expansion cap, is the top hose hard with the high pressure. ??
With the rad… try flushing, best way is a reverse flow, but a bit of an involved job removing the rad if yours incorporates the oil coolers.

RangeRoller dt · Aug 8, 2021

You should test a new stat by tying it to a wire and dipping it in a pan of boiling water. should open fully at the temperature stated on the unit and close once cooled on its own.

kermit_rr · Aug 8, 2021

RangeRoller dt said:
You should test a new stat by tying it to a wire and dipping it in a pan of boiling water. should open fully at the temperature stated on the unit and close once cooled on its own.

And note the petrol one actually has 2 valves that open/close, one for the bypass and one for the actual radiator

tomcat59alan · Aug 9, 2021

kermit_rr said:
And note the petrol one actually has 2 valves that open/close, one for the bypass and one for the actual radiator

Another positive point for the diesel,at least ours isn't in an enclosed housing.

dubbleRR · Aug 9, 2021

If the rad is the same as a diesel one ,theres a baffle in the top that forces water down one side n up the other side ,if its failed then water just flows across the top ,,check the rad for heat at the bottom should be hotter at one side n cooler at the other , a scope and torch or marble test

kermit_rr · Aug 9, 2021

dubbleRR said:
If the rad is the same as a diesel one ,theres a baffle in the top that forces water down one side n up the other side ,if its failed then water just flows across the top ,,check the rad for heat at the bottom should be hotter at one side n cooler at the other , a scope and torch or marble test

its not the same as the diesel one.
The test I did on mine, place radiator on a flat surface, fill with hot water from a kettle as quickly as possible, then use IR thermometer to look for any hot/cold spots

pwood999 · Aug 11, 2021

Flush the whole system, not just the rad.
Is it losing coolant or just overheating ? Any leaks will prevent the system getting proper pressure, and it will boil.
Check the un-obvious like core plugs, underneath throttle body heater, etc.
Also do a pressure test when the engine is warmed up, and not running so you can see any leaks.

Air locks should be sorted by following the RAVE procedure rather than the top hose.

Dippypud · Aug 11, 2021

pwood999 said:
Flush the whole system, not just the rad.

Is it losing coolant or just overheating ? Any leaks will prevent the system getting proper pressure, and it will boil.

Check the un-obvious like core plugs, underneath throttle body heater, etc.

Also do a pressure test when the engine is warmed up, and not running so you can see any leaks.

Air locks should be sorted by following the RAVE procedure rather than the top hose.

And is the internal footwell carpet wet ? With coolant ...

Mark Piercy · Aug 11, 2021

If none of the above, a compression check on each cylinder with the Throttle wide open for any differences between cylinders.
Pull your rad out also and look for dead leaves mouse nests and dead birds jammed up in there reducing air flow. As said above.

Grrrrrr · Aug 11, 2021

Mark Piercy said:
If none of the above, a compression check on each cylinder with the Throttle wide open for any differences between cylinders.
Pull your rad out also and look for dead leaves mouse nests and dead birds jammed up in there reducing air flow. As said above.

Dead birds? Sure you don't mean peasants?

Mark Piercy · Aug 11, 2021

I thought you wrote peanuts

Grrrrrr · Aug 12, 2021

Mark Piercy said:
I thought you wrote peanuts

Snoopy would be upset.

oakey · Aug 12, 2021

Look up in where for a dead bird? Is that to check if dead?

Mark Piercy · Aug 12, 2021

oakey said:
Look up in where for a dead bird? Is that to check if dead?

Up against the front of one of the rads, maybe even a nest if the car hasn't been used for a while.

tomcat59alan · Aug 12, 2021

oakey said:
Look up in where for a dead bird? Is that to check if dead?

My neighbour thought he'd hit a pheasant a couple of days ago,he stopped but couldn't find it, when he got home he as a proper look and found it had been forced through the plastic grill ( Honda) and was against the radiator. His wife wouldn't entertain eating it????.

kermit_rr · Aug 12, 2021

tomcat59alan said:
My neighbour thought he'd hit a pheasant a couple of days ago,he stopped but couldn't find it, when he got home he as a proper look and found it had been forced through the plastic grill ( Honda) and was against the radiator. His wife wouldn't entertain eating it????.

isn't there some daft law that says you can pick up roadkill, but not if you hit it?

P38 v8 Petrol Overheating

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