Funny Overheating Problem with Carby V8

Davo I think that you will eventually find that it is head gaskets.
You have not posted what the compression test results were AFAIK.
What were they?

I had this problem once in Saudi and pulled the heads finally to find a track burnt in the gasket and head between a cylinder and the valley.

This usually also causes excessive oil leaks as it pressurises the block.

Another "way out" cause may be that your front pulley TDC is not actually TDC. Maybe make up a tool by drilling a spark plug and placing a rod in, and turn the engine until it is highest on no1, then do it the other way. the mid point between will be TDC.
Regards Philip A

Jake, if your top hose is getting pressurised then I wouldn't be surprised if it's the head gasket. So you haven't done a compression test yet?

Philip, I did indeed check for real TDC and was quite disappointed that it was correct! That would have been an easy fix. But I suspect you're probably quite right about the head gaskets. I just haven't had the associated coolant problems.

I've got the compression test numbers here somewhere and they were about right, but I should do it again. But the thing that's got me is that I just can't get the mixture right with a Colortune, and the plugs are always white after a run, even if the engine behaved and didn't run hot. That's why I think the cam and chain are stuffed, and I figured that since I've got a new engine here anyway, (meant for the poor Landie), that I may as well finish it off and get some use out of this damned Range Rover.

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But I suspect you're probably quite right about the head gaskets. I just haven't had the associated coolant problems.

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The only time that you ever have coolant problems with blown head gaskets with an RV8 is when an end cylinder is involved as the only waterways from the block are at the very ends. In many cases this is where they leak , but in a lot it is a middle cylinder.

In the case of a middle cylinder blowing some people assume it is a head gasket as they have coolant problems when it is a slipped sleeve.

In the 3.5s , the fifth head bolt on the outside would "jack" the head upwards in the middle towards the V , if the bolt was torqued to LR spec.This is why it was deleted in later engines.
Regards Philip A

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But the thing that's got me is that I just can't get the mixture right with a Colortune, and the plugs are always white after a run, even if the engine behaved and didn't run hot

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You should count yourself lucky if you have white plugs. IMHO this is not the cause of overheating. My 3.9 runs white plugs all the time with its o2 sensors keeping the mixture at 14.2-14.7:1. As long as it doesn't stumble etc it should be fine as you don't use enough accelerator while cruising to cause overheating.
As carbys wear the needle and main jet wears down and the mixture becomes richer, and the usual worn condition is a rich mixture that you cannot lean out. I had to get new needles and jets once to pass the unburned HC ADAC inspection in Saudi.

My recent experience with a worn cam suggests that this is also not the cause of white plugs. What happended in my case is that as the lobes wore out the valves do not open and the plug tends to foul with oil. Of course this may not happen in all cases.

Regards Philip A

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Originally Posted by PhilipA

The only time that you ever have coolant problems with blown head gaskets with an RV8 is when an end cylinder is involved as the only waterways from the block are at the very ends. In many cases this is where they leak , but in a lot it is a middle cylinder.

In the case of a middle cylinder blowing some people assume it is a head gasket as they have coolant problems when it is a slipped sleeve.

In the 3.5s , the fifth head bolt on the outside would "jack" the head upwards in the middle towards the V , if the bolt was torqued to LR spec.This is why it was deleted in later engines.
Regards Philip A

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Next job is to pull the plugs and inspect for any "steam cleaning". Then do a compression test and a gas test of the coolant.

If it's a head gasket, I'll probably just source a 3.9 or 4.6 EFI engine. My carbys are old and shot and don't keep tune anyway, and I have some cam follower noise. Why keep a 3.5 LC engine which only converts petrol into noise? I may as well get some extra ponies for my money.

Otherwise it's a Lexus V8 or an Isuzu 4JG2T: pulling the 3.5 to repair means a lot of labour anyway, so I may as well put in something that CAN haul the weight around.

Jake - 'cause the 3.5 doesn't tend to drop liners!

Philip, you make some great points there. Mind you, I've seen the cam when I had the sump off and it's a bit "brown", looking pretty worn. And the engine does have evidence of being full of the usual black gunk, until someone put some cleaner through. And I just plain forgot about the coolant galleries only being at the back of the head gaskets.

I'll have to do another compression test soon.

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Originally Posted by Davo

Jake - 'cause the 3.5 doesn't USUALLY drop liners!

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Fixed!

Picky . . . :p