Funny Overheating Problem with Carby V8

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Davo
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Funny Overheating Problem with Carby V8

Post by Davo »

I posted this over at an Australian Land-Rover forum that I'm on, and when someone said that this may be the start of a head gasket leak I thought it would be a good idea to post my question here, since such gasket leaks are no doubt well known by some!

Here is what I posted in the other forum:

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!



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Ian Anderson
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Post by Ian Anderson »

Davo

welcome to the madhouse

On your heater Matrix bypass you have made a perfect loop for the coolant to get around without going through the radiator.

How do I know I did the same and had the same results - temperature swings bigger than my wife's mood swings!

What I did
Length of 15mm home plumbing pipe (5 - 6cm long) soldered on an "end stop" that would normally be used to block off the pipe as if you had removed a sink.

drilled a 1.5 - 2mm hole in the end stop

Cut "loop" hose and insert piece made above fixed with 2 jubilee clips

It allows fluid to move a little and clear out any bubbles but not enough to allow any meaningful water flow thus forcinf all the flow through te radiator and thermostat

For 10 mins work and aout £5 for 2 jubilee clips it was worth a try and worked wonderfully

Ian
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Post by jimbob »

That's a tip tip.

I have the LR plastic directing valve o re-direct the coolant water.

This is even better.

Davo
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Post by Davo »

Thanks a lot, guys. You know, at one point I did block off the outlet at the back of the inlet manifold, left the pipe underneath empty, and blocked off the inlet at the back of the timing cover that the pipe was connected to, reasoning that they weren't needed without a heater.

It most certainly didn't work, so that's when I went to the U-shaped hose to connect the two pipes at the back. But still, that's directing a lot of hot coolant back into the water pump. Perhaps I might plumb the heater back in.

What's this plastic directing valve that you speak of?

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Post by Ian Anderson »

Just make a restrictor plate with a small hole in it - it is like you have the heater on a little with a small flow of hot water through it.

Trust me it works!

Ian
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Post by Ian Anderson »

Oh yes and if you'd like to google it there is a pile of stuff written about this. MGB V8 ran faultlessly through the summer but in the winter put the heater on and suddenly the car overheats - too much flow through the heater meaning no flow through the radiator

Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.

Davo
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Post by Davo »

Thanks again, fellas, that's good stuff. I was thinking about when I blocked off those bypass parts, and now I can't remember if that's when I also had the bad new thermostat. Maybe I blamed the bypass when it was actually the thermostat. (This comes from making too many changes at once - and I should know better by now!)

I'll make a little plug with a 3mm hole in it to go into the U-shaped hose I've got at the back of the manifold.

I might also reconnect the heater as an experiment. I disconnected the heater because I was worried about it failing, (we live in the middle of nowhere here, and what's worse, in Toyota country), since on a Rangie the coolant always flows through the heater. There's no valve that stops the coolant flow. I'd bet that only flowing through the heater core cools the coolant enough so that it doesn't just feed heat back into the system - as it certainly does now!

Why wasn't this obvious to me before????? Sometimes things just need pointing out . . . (sigh)

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Post by DaveEFI »

The heater thing may be a red herring. My SD1 with air-con has a cut-off valve in the heater water supply operated when the heat control is on minimum.
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Davo
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Post by Davo »

Well, I fixed it. I did put a restrictor in the heater bypass but the problem was a bit simpler than that! I'll just paste what I wrote on the other forum, since it may help someone else. Pardon the second-hand posting, but it's a lot of typing!

I checked the timing was at 6 BTDC and replaced the ignition module, and used a big syringe to put a bit of vacuum onto the vacuum advance and make sure it moved and stayed put. (They're well known for leaking.)

All was fine but when I pulled out the plugs for the compression test they were all white. I did find that by richening the mixture the cooling problem seemed to be fixed, but the original carbies were in the usual original condition so I replaced them with some new ones I had.

That's when my problems really started, because no matter how rich I made the mixture, the cooling problem was there and the plugs would be white after a run. It's at this point that I started keeping notes so I could see what I'd done and not rely on my dodgy memory!

I tried cooler plugs, going from NGK BP5ES to BP6ES. It also seemed like there was just too much air getting in, so I went right through the breather system and checked everything. Then I went through the brand-new cooling system, and tried taking the guts out of an old thermostat and putting that in.

I kept ignoring the timing as it was set at 6 BTDC, as per the manual, but then I saw a neat quote on a website that, "90% of carburettor problems are electrical", and realised the timing would be worth looking at. 9 degrees was better and then 12 BTDC transformed the old car, making it take off quicker but also suddenly the cooling was normal. It would heat up slightly under load or while idling, as normal, and once on the highway it would cool down again, the way it was supposed to.

So the lesson here is to be methodical, keep notes, and check the simple and basic things first. Once I'd replaced the cooling system and the compression test was good, it had to be something else. As any old hand here will know, if I'd done that in the first place I would have saved myself a heap of trouble.

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Post by ramon alban »

Hello Davo, You may have an Ooops! I suspect you may well have hidden the overheating problem temporarily by over advancing the ignition timing and you are getting a cooler burn because the actual fully advanced timing is now at (say) 35 to 45 degrees BTDC and the mixture is being part burned before it is fully compressed.

If like most folk you are running premium unleaded then the idle ign timing normally has to be retarded by 4 - 6 deg to say 2-4 deg BTDC.

Thats a lot of difference to your current 12.

As for the overheating, the symptoms you describe seemed to indicate that the system has trapped air and it really needs a good burping.

There is some stuff you may want to consider regarding ignition timing and getting rid of airlocks here:

http://www.vintagemodelairplane.com/pag ... ion02.html page 4 of the pdf onwards.

and

http://www.vintagemodelairplane.com/pag ... ant01.html

Hopefully it can be adapted to your engine.

Davo
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Post by Davo »

Okay, thanks for the tips. I'm sure there isn't any air trapped as it bled pretty well, and I've got a filter in the top hose with a cap on it, so it's easy to check this point in the system. But as with anything else, it's certainly worth looking into.

Great ignition articles, too. Thanks again!

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Post by Davo »

And the problem came back, just before a Christmas trip!

Same thing - a timing advance made a difference to the power, but by now even I could see that it was a bandaid solution.

So, now I'm looking at a cam change. I knew it was worn, but it must be much worse than I thought, and obviously the timing chain is rooted, too.

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Re: Funny Overheating Problem with Carby V8

Post by Davo »

You know how you post something and mean to get back to it, and then Life tangles itself up and you forget . . . for a few years?

So I did fix this, and it's embarrassing to admit it, but I'll do so in case it helps someone else. The one part I thought beyond suspicion was the culprit - the new radiator. It was an expensive G&M "Tropicore" so I naturally thought it would be okay. Eventually I just put in a good used rad and instantly the engine was fine. Confused, I finally worked out that G&M has sneakily been using cores with fewer tubes and fins per inch. The used one had many more and I realised that the new rad did look pretty sparse. I've since seen another new G&M radiator and it was the same thing. So never again!

Oh, and a Chinese ally rad is in there now . . .

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Re: Funny Overheating Problem with Carby V8

Post by ChrisJC »

Nice data point - thanks!

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Davo
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Re: Funny Overheating Problem with Carby V8

Post by Davo »

You're welcome! I do a tube-and-fin count before buying a radiator now . . . if only I'd known!

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