P38A M51 diesel cooling improvement.

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Datatek

Datatek

Well-Known Member
Posts
44,890
Location
Near Poitiers SW France
I was recently contacted by Sam Early from New Zealand for details of my aircon fans mod. He was already running his P38 diesel without the viscous fan using an after market fan and had no problem until he came to tow a boat in hot weather. It gets hot in NZ!

I thought that the additional cooling from the aircon fans might not be the answer, what was needed was a replacement for the inefficient P38 RAD. Only one half of the RAD gets coolant at full temperature, coolant going down one side and back up the other side. As the rate of heat loss is dependant on the temperature differential between the coolant and the air, only one half of the RAD gives the maximum cooling. Add in the fact that there is a good bit of flow past the baffle straight across the header tank and the RAD is not as effective a it's size would suggest.

I have looked at a number of different RAD's to put a full flow replacement in but not found anything.

Sam has come up with the answer, the early GEMS V8 RAD can be squeezed in, it's a tight fit needing the guide bolts loosening. The top hose is a straight fit, it just needs a bit of plumbing to connect the bottom outlet of the RAD. Apparently, even the cowl can be refitted with a bit of trimming if the viscous fan is to be retained.

I have run with the viscous fan and cowl removed for a few years now without a problem even in hot weather but I've always been aware that cooling is marginal. Changing the RAD gives a much greater margin of safety. It has certainly cured the problem Sam had.

I will be doing this mod to my P38's in due course.
 
Datatek said:
I was recently contacted by Sam Early from New Zealand for details of my aircon fans mod. He was already running his P38 diesel without the viscous fan using an after market fan and had no problem until he came to tow a boat in hot weather. It gets hot in NZ!

I thought that the additional cooling from the aircon fans might not be the answer, what was needed was a replacement for the inefficient P38 RAD. Only one half of the RAD gets coolant at full temperature, coolant going down one side and back up the other side. As the rate of heat loss is dependant on the temperature differential between the coolant and the air, only one half of the RAD gives the maximum cooling. Add in the fact that there is a good bit of flow past the baffle straight across the header tank and the RAD is not as effective a it's size would suggest.

I have looked at a number of different RAD's to put a full flow replacement in but not found anything.

Sam has come up with the answer, the early GEMS V8 RAD can be squeezed in, it's a tight fit needing the guide bolts loosening. The top hose is a straight fit, it just needs a bit of plumbing to connect the bottom outlet of the RAD. Apparently, even the cowl can be refitted with a bit of trimming if the viscous fan is to be retained.

I have run with the viscous fan and cowl removed for a few years now without a problem even in hot weather but I've always been aware that cooling is marginal. Changing the RAD gives a much greater margin of safety. It has certainly cured the problem Sam had.

I will be doing this mod to my P38's in due course.
Click to expand...

Thanks for the info that sounds like the way to go and an easy answer, wonder why landrover never did it like that in the first place.
Nice to see you popping in from time to time:):):)
 
Quote;
I have run with the viscous fan and cowl removed for a few years now without a problem even in hot weather ............ unquote,

hot weather means around 35 C or higher?
 
kapilamuni said:
Quote;
I have run with the viscous fan and cowl removed for a few years now without a problem even in hot weather ............ unquote,

hot weather means around 35 C or higher?
Click to expand...
38C three up with luggage up hill in slow moving traffic, no problem. Fans going flat out!
I have also towed a trailer with a dead P38 on it with the temperature in the mid 20s C, again no problem, but I wouldn't bet on doing that in higher temperatures. Sam has shown that the RAD change will allow high temperature towing.
 
I've still never had any issues with my viscous fan, even with 3 tons of digger towing behind me. Admittedly this wasn't at 28 degrees celcius. Mud and gunk in the fins won't help, especially if you've been wading in mud.

Never tried Direnza but interested to hear how you get on.
 
That's tempting. Here the temps are around 30 C but in April it goes up to about 35 C max.
But in a similar situation like you mentioned, my gearbox would have cried- 'gearbox overheat'-check hand book'.
Even 1/2 hr in very slow traffic, flat road, it cries.
 
kapilamuni said:
That's tempting. Here the temps are around 30 C but in April it goes up to about 35 C max.
But in a similar situation like you mentioned, my gearbox would have cried- 'gearbox overheat'-check hand book'.
Even 1/2 hr in very slow traffic, flat road, it cries.
Click to expand...
If the auto box oil cooler has a fan fitted, it probably is not working. If it doesnt have a fan fitted as on early cars, fit one.
 
dubbleRR said:
Has any one tryed the all alloy rad on the bay,of,e Its a DIRENZA Its a twin core .;)Think its 50mm diesel and 60mm petrol....
Click to expand...
The Direnza RAD for the P38 is IMO pointless as it still has the flow and return at the top meaning that only half the RAD is fully efficient. The GEMS RAD is half the price.
 
Fair point ,It look stronger and being all alloy thought it might cool better...But it all comes down to air flow n viscous working at its best..,but if the expansion tank had a water level sensor that would save a lot o diesel heads..:rolleyes::D:D
 
dubbleRR said:
Fair point ,It look stronger and being all alloy thought it might cool better...But it all comes down to air flow n viscous working at its best..,but if the expansion tank had a water level sensor that would save a lot o diesel heads..:rolleyes::D:D
Click to expand...
Sorry but a water level sensor would not help as long as you do your weekly level checks, it just removes responsibility. Water loss usually occurs as a result of the overheat blowing the water out, unless the RAD or a hose splits, and it is the overheating that causes head failure
 
Aye But what if you lose water on the move .. it would give you time to pull over and save the engine.The gauge.goes up the red light comes on ,the radio gets turned down and at that point its too late:eek:then thought turns to money:D:D:D:D
 
In addition to low efficiency of the radiator, viscous fans inability to do the job at low RPMs is a reason , I think.
After removing the viscous fan installing a set of electric fans to support the AC fans should help. Seen VW Tourag 3.0 TDI V6, having
no VC fan but two electric fans.
 
kapilamuni said:
In addition to low efficiency of the radiator, viscous fans inability to do the job at low RPMs is a reason , I think.
After removing the viscous fan installing a set of electric fans to support the AC fans should help. Seen VW Tourag 3.0 TDI V6, having
no VC fan but two electric fans.
Click to expand...

Only if the viscous fan is knackered.
 
Mod done without removing VC fan. Found a radiator fan of a diesel BMW 320 - E46 (marked 400W ) with that I intend to replace the VC fan. That demands about 35 A and with full load , (AC fans, blowers, ABS pump,wipers, head lights high beam, fogs etc) will the alternator (105 A VALEO) stand upto it?
Anyone knows what the wattage under full electrical load?
 
With good viscous fan(genuine) and good clean radiator(60mm thick core) i've never had problems with overheating.
No electric fan will give more airflow than original 11 blade viscous fan unless it's few kilowats power.
 
Mine is not overheating. That era passed after changing the HG. I don't pull caravans.
My VC fan is from 300TDI which is a direct fit bought new , genuine about 2 years back.
The radiator is the one came from the factory yet it's fine.
I just want to get rid of the habit of eyeing the temp gauge & the feeling that the needle will go to red the next moment.
In addition to what datatec pointed about the radiator, I noted that the VC fan is not centered on the radiator (on a vertical axis).
It's more towards the RHS. Should not it be more towards the LHS where hot coolant flowing in.?
 
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