Disco 1 intermittent "almost" overheating

[bsa_m21]

So I was up the sunshine coast this past week. Although we were only doing 80-90kph on the highway, intermittently the temp would rise almost to the top of the "OK" scale. I would put on the A/C fans with little impact, until I tuned up the heater temps. It would then drop back to 1/2 way (normal). I could then turn off the heater and A/C and she would be fine again for an extended period, then it would repeat. At high speed (100kph+) she is fine. At low speed she is fine.

So far there is no coolant loss and the system is not over-pressurized, no plugs are washed and oil is clean (just changed last week). I noticed yesterday that at low speed under load (going up a steep hill near home), the temp started to climb quickly.

I've done the following with no change to this behaviour so far:
- separated the A/C and engine rads and cleaned between them and blew out the vanes in both rads.
- replaced the thermostat with a 180F, with the bleed hole at the top.
- replaced the coolant

I'm kinda hoping I don't need a new rad or recore, or a new waterpump. Any suggestions as to what to try next would be appreciated.

Regards,
M.

[red90]

Most likely cause is the viscous unit on the fan not locking up. You need to check it when it overheats to see if it is locked. It is an on/off type of locking and you can usually hear the change in fan noise when it locks. They fail fairly regularly, but are only needed rarely, so it goes unnoticed.

[bsa_m21]

Well, I pulled the rad and took it to the Rad shop in Langley. 30 seconds of testing and he says it's mostly plugged and he's amazed the truck ran cool at all.
He's going to boil it out and hopefully that will fix it. Otherwise, I guess I'll have to buy a new rad of Ebay. They go for anything from US$180 to over $500. Not too sure why the huge difference.

Ah well, it's only money.

M.

[harv]

I don't know specifically about Disco rads, but in general there's a big difference in the quality of them. A cheap one might not last very long.

[bsa_m21]

Well just heard back. Rad needs a full recore at > $500. So, I ordered a mid range rad from ebay, and a new viscous coupling. Should have them by Friday. Pics once I get them.

M.

[ANDYD]

Its good you found it before overheating the engine, those V8's really do not like being overheated ...

What was the rad plugged with? Was it just rusty deposits / sludge / pine needles / or .... :shock:

I wonder is someone (PO) has been pouring in the "Rad-Weld" in the past to fix an old head gasket problem.

[bsa_m21]

Not sure. After the call from the Rad shop that I needed a rebuild, I told them to junk it. So I never bothered to take the rad apart to see what plugged it.

However, it did show some signs of past leaking, so it's likely someone added some stop leak gunk into the system. Also, the thermostat I threw away, worked, but was fairly gunked up at removal.

Should have the new parts by end of day Friday and will re-assemble first thing Sat. Will let you know what temps she is running at afterwards.

M. :bounce:

[bsa_m21]

Well the border line up Friday was ridiculous, but I made it through and got my new rad. Took ten min to install the new rad and viscous coupling, another 10 or so to feed liquid to the old girl and burp her a few times. Now she is running as cool as can be. Yay!
The empty slot:

IMG_2283-1024.jpg

(77.36 KiB) Downloaded 2561 times

And the new Rad

IMG_2284-1024.jpg

(89.82 KiB) Downloaded 2561 times

[BlkP38]

Martin,
I think I bought a rad from you last year at Founders Day. Shame I did not see you looking for one.
Anyway, I have a couple of new rads available. I think they are to same for a D1 and a 90/110 300 tdi. Chime in if I am incorrect.
Eric.

[bsa_m21]

Not me. Never sold a Rad to anyone. :oops: