Funny Overheating Problem with Carby V8

**Davo** · 26th July 2011, 10:50 AM

I've been chasing this problem since last year now, but every time I think I fixed it, it's still there.

1983 Rangie auto, with plain old carby V8 and aircon. When I got it, it had a metal fan on the water pump from something else that somebody had put on. I replaced the radiator with a brand-new one - proper aircon spec - and a new Genuine Parts 74C thermostat, and put in a capillary type temperature gauge as the standard one didn't seem to know what it was doing, (as usual with these old gauges). And I also put in a Watchdog TM2. As well, I gave the engine a good flush and bypassed the heater by connecting the two pipes at the back of the inlet manifold, which is what the parts book shows for V8 Defenders with no heater, so that should be okay.

With the new gauges, I could see this funny problem. Everything would be fine when idling, or cruising around town at 50kmh, but out on the highway it would quickly heat up to almost 100c, and then the temperature wouldn't come down again with town driving or idling. I finally worked out that the new thermostat wasn't opening all the way and put in one that would, and the problem was much better. But now it was after a highway drive that it would start running too hot in town.

Not long afterwards, I replaced the water pump as the old one developed a squeak, but the new one had a different stud pattern and while the original double pulley would fit, the old metal fan wouldn't. So I went to EL Falcon thermos, which seemed okay - until a drive to Broome on a 26C day and they had to be left switched on for a good deal at the end of the trip, so obviously something was still wrong.

So . . . thinking that perhaps the thermos weren’t up to it for some reason, even though other guys are happy with them, I got the original type plastic fan and viscous unit and shroud, and found that, after all, that hasn't made any difference. It's still a concern now as the temperature is fine while highway cruising but then it heats up rapidly while town driving afterwards, to the point where I'll manually switch on the aircon fans to keep it at 92C, and this isn’t in hot weather. Otherwise it can hit 97C on the Watchdog and that’s too high for me.

Using a laser thermometer, the most heat seems to be around the thermostat housing and the bypass hoses - those two hoses that go into the back of the timing cover. It's tempting to think that it's the new new thermostat not allowing enough flow, or maybe the new radiator isn't so good, since it’s the new parts you should suspect first.

So now I’ve got a new rad, water pump, thermostat, hoses, belts, viscous unit, fan, cap – in fact, everything you can replace except for the actual engine, which is fine by me. The engine heats up at a normal rate, and is okay around town until I get back from a highway run. It doesn’t seem to run too lean and I haven’t found any intake leaks, (unless the charcoal canister is no good).

And now I’m very tempted to put in a thermostat with the middle cut out to get better flow . . . but I realise that’s more of a bandaid solution. I might put the old radiator back in soon, just to see what happens - I’m pulling my hair out over this one!

**PLR** · 26th July 2011, 05:07 PM

G`day ,

We have an 85RR that acts the same way when it is in the starting process of a leaking head gasket .

( It`s due for its 3rd set now since we`ve had it , before always does as said after does not . )

Further into the gasket leak it will then do the same on the gauge and spit fluid and hold pressure in the system when worked , eg, tow trailer .

At the same time as spitting if not worked it will just show a rise on the gauge when slowing after highway speeds but the falcon thermos keep the temp in check , just run a bit longer . The falcon viscous set up would not keep up .

If you can i`d suggest you check for gasses inside the coolant system .

Peter

**Davo** · 27th July 2011, 10:29 PM

Thanks for the tip, Peter. I'll see if anyone in town can test the coolant and I'll have to get around to doing a compression test, though they're a bit annoying to do. I know the cam is getting on a bit so it may well be time to do that and the heads, but I'll hate to tell the wife when the time comes given how much trouble we've with this old car had so far!

**roverv8** · 28th July 2011, 06:54 AM

Do you still run points in the dizzy or upgraded to electronic Ignition?

**PhilipA** · 29th July 2011, 06:48 PM

I dredged this from memory and hope that it may help.
On carby RV8s there is a small hose that runs from the middle of the riser in the inlet manifold to the radiator header. As the riser is the highest point on the engine if the hose becomes blocked an airlock forms and causes the problem you describe.
The part that blocks is the stub that the hose fits on at the manifold riser. just get a drill and work it through the stub to clear it.

Be great if it is the problem.
Regards Philip A

**Bushie** · 29th July 2011, 08:47 PM

When you replaced the waterpump what was the timing cover like behind the pump ? They can be subject to erosion of the case, between the two heater hoses out the back of the pump, that allows some water to bypass.

Mine (when I had it) also developed a small hole in this area, but some epoxy fixed it.

Martyn

**Davo** · 29th July 2011, 09:29 PM

I tried posting this earlier, but the system was down again.

Anyway, when I got it last year, it had the original points dizzy with an Optospark electronic conversion, and then I put in a Lucas 35DM8 that I had from another 3.5 V8. That's the distributor with the coil and ignition module all mounted together away from the dizzy.

Yes, I did put in a new timing cover while I was at it as the old one was utterly stuffed, far worse than any other I've seen. And I have cleared out that little stub you mention, Phil, but naturally I haven't checked it since then, so thanks for the reminder.

**Tank** · 30th July 2011, 12:24 AM

Sounds like head gasket problems to me, also does the vacuum advance work, Regards Frank.

**roverv8** · 30th July 2011, 02:23 AM

Originally Posted by Davo

I tried posting this earlier, but the system was down again.

Anyway, when I got it last year, it had the original points dizzy with an Optospark electronic conversion, and then I put in a Lucas 35DM8 that I had from another 3.5 V8. That's the distributor with the coil and ignition module all mounted together away from the dizzy.

Yes, I did put in a new timing cover while I was at it as the old one was utterly stuffed, far worse than any other I've seen. And I have cleared out that little stub you mention, Phil, but naturally I haven't checked it since then, so thanks for the reminder.

Check your timing with a light, checking it's consistant when reving.
Had a similar overheating problem years ago with a CM Chrysler,
found that the timing was bouncing all over the place, and advancing way to much when reving,
It seemed to go ok but had a crook ignition module
Worth a look

**Davo** · 30th July 2011, 04:31 PM

Geez, what a list. This will be handy for someone doing a search one day.

I also posted this over at The V8 Owners Forum - :: Index and some guys there reckon that bypassing the heater sends too much uncooled coolant back into the water pump, which sounds reasonable since the bypass makes two hoses going straight from the inlet manifold and back into the water pump.

So I'll check, in the order of easiest first:
- Ignition timing
- Vacuum advance unit
- Ignition module
- Hose stub at top of manifold between carbies
- Heater bypass
- Head gaskets

And actually remember to post the results so that it may help somebody else. Thanks again!

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