Thread: D2 overheating TOTALLY FINALLY solved v8 and Tdi

Originally Posted by AK83

---
So how did they get away with the cold-hot-cold-hot-... routine for all those years prior to the new fangled way?
600+ K klms from my old RRC with nothing done to the engine and it still went OK.

it went 600K because it DIDNT go hot-cold, ( and wasnt pre-set to run at 96)...
From the factory the block temp is regulated by bleeding water in from the rest of the system,
if you have overheating problems you have a problem! () head gaskets usually, maybe its just a radiator (that could be 18 bloody years old by now)
The only thing wrong with the D2 cooling system is the temp of the thermostat.

Originally Posted by AK83

Is the 3.9/4.0 L version of the block really all that much different to the older 3.5 L engine?
Heads?
While the twiddled and tweaked a bit here and there, the same basic materials and technology of the castings remained the same.

So how did they get away with the cold-hot-cold-hot-... routine for all those years prior to the new fangled way?
600+ K klms from my old RRC with nothing done to the engine and it still went OK.
(A front main seal would have stopped the Exxon Valdez like oil slick after a long hot quick run .. but the car was well past it's use by date by then anyhow).

I just inherited a V8 D2 myself and have a plan to get it back on the road (if it's economical enough)
It's apparent history is the familiar story of one of the previous owners getting fed up with the overheating issues it gave them, and got rid of it cheaply. Various hands later and now it's in my drive waiting for a resurrection.
If the overheating issue turns out as bad as the previous owner had to deal with, I'll be looking to do the same mod too.

3.5 litre blocks have a thicker layer of cast alloy around the liners as they are 89mm bore and there wouldn't be room for cooling water between the bores at 94mm if the alloy wasn't thinner. I once plugged some known thickness numbers into a fatigue failure formula for cast alloy and found that the 3.9 and onwards blocks should on average last 1/3 as long as a 3.5 block before cracking, all other things being equal. This roughly equates to an average block life of 250K for a 94mm bore and 750K for an 89mm bore block. Clearly 250K is enough to get the engine through warranty and the inevitable new car upgrade cycle but it means there won't be too many around in another 25 years.

As for hot/cold cycling, all 3.5 engines have a 3/4" bypass hose from the inlet manifold behind the thermostat to the back of the water pump. This does keep the engine temperature quite even under normal operation. The D2 engine does the bypass externally with bigger hoses and the 3 legged thermostat, the major difference being that the bypass closes when the thermostat is fully open. Clearly if the thermostat fails to seal the larger bypass then the engine won't get full cooling flow at elevated temperatures. I'd like to see a replacement alloy housing to carry an off the shelf bypass thermostat but I suspect the market would be very limited as D2's are nearing the end of their plastic limited existence.

Originally Posted by Pedro_The_Swift

I understand why someone would bite that bullet and change the way the coolant works in a D2,,
A D2 V8 is worth nothing once it overheats, and if the whole car has cost you peanuts then why not?

BUT once you've spent some serious money (invested in the car or) on rebuilding one,,
its not so simple,,
I have absolutely NO inclination to have my block go
hot-cold-hot-cold-hot-cold,
because however you describe the new system, the manufacturers system is all about a constant engine block temperature,,
is it set too high from the factory?
Yes!
Can you reset it to run at the SAME temps as this thread says?
Yes!

You guys go hard,, I hope your system stops the liners from dropping,,
but as the rate of different metal expanding with heat is the problem, I really cant see it,,

just my opinion,,

Are you are referring to the inline mod when you say you don't want your block going hot-cold-hot-cold. If so, what makes you think that happens with the inline mod?

I drilled to holes in the thermostat inline. When I opened my TEFBA filter lid that is between inline stat and radiator and bled the system Cold the water quite quickly filled the top hose and filter. .in other words it is bleeding quite a flow of water when thermostat is closed. Providing you have that bleed there shouldn't be problems. In the US many people have done the inline mod and no reports of problems. I may keep mine or may go back to an 82 3 way depending on how it goes.

Cheers

the inline mod removes the bypass flow the block heats up quickly and then the thermostat begins to open as the flow through its 1/8th inch bleeder warms it up. a flow of now hot coolant hits it and it opens quickly. The entire content of cold water in the radiator enters the engine the coolant temp comes down the thermostat closes up the flow slows down and in extreme cases stops.

The cold coolant in the block heats up in the radiator cools off and the process repeats as the small 1/8th bypass hole allows the reheating coolant to warm up the thermostat again.

in engines where the thermostat is part of the head/block the repetition is slower due to the mass of the metal and heat from the block/head.

The trick to slowing it down to nearly completely preventable (without doing exotic things with electric pump and fan managment) would be to drill about 1/3 of the total primary thermostat hose cross section through the thermostat flange to allow a reasonable flow of coolant preventing the thermal cycling but thats going to slow down your warm up and sounds suspiciously like its just been made into a bypass thermostat setup...

The D1 bypass is merely to allow hot and getting hotter water to move around the block,heads and heater matrix ...not sure that it would move around much given that the water pump is not a pressure pump. The thermostat on a D1 has a little air bleed hole that faces the top of the housing and apart from that allows NO flow until it starts to open. I don't see the D2 inline as being materially different provided the housing is nice and close to the outlet pipe from the intake manifold.

So today at highway speeds a rock solid 84 degrees C for 30 mins of driving at 35 degrees c outside ambient. Then got home and it idled up to 87 with air intake getting to 64 and it got no warmer than 87.

I think in winter a thermostat with only 1 bleed hole might be the go but it's cheap as chips to change and a very easy quick exercise to change for the season.


I am loving the low temps.

Ps Pedro what temps are you getting on the highway in say mid 30 degree days (not towing)?

Cheers

Idling for 10 mins after highway run...

Check out intake air temp.


20170130_155309.jpg

On saturdays run to Brizzy it sat on 86-87 for an hour at 100.
The caravan doesnt really affect it running down the highway at 100.

Over Chrissy it sat in a bunnings car park for 15minutes idling, it was one of those white cement car parks that burn your retinas out, the OBD2 said 87 when we drove in, the car said 35 outside, 15 idling minutes later the obd2 still said 87 as we drove out.