Engine and Transmission Tech

Rover V8 3.5 runs too cold with 82 stat - barely above C and heater tepid.
But too hot with 88 stat - even in cool weather it's nearly at H and loses a little water, can't see where.

I think to drill a small hole in the rim of the 88 stat.
What size hole would make a difference?

Ivor

Something is wrong Ivor.
A 6 degree difference shouldn't be that dramatic.
Drilling a hole in the tstat is meant to pass air along to prevent an airlock.
Having said that a 1/8 inch hole drilled on the uppermost side (the high side where air would tend to collect) of the tstat is what's normally done.
With very little information, I suspect that you have a head gasket problem. The lower temp tstat opens early allowing the airlock to pass through. The higher temp one opens too late and aggravates the issue.
Open your rad cap and smell the coolant. Does it smell like exhaust? Alternatively you can buy dip strips to test for hydrocarbons.
Does the engine run rough on a cold start, for a minute or so? This indicates coolant in a cylinder that takes time to clear out.
There are many other issues that can cause this problem. But if this is a recent development, my money is on the gaskets.
Cheers
Fred

Fred, thankyou.

The engine was swapped in, mid 2017. Said to have 25,000 from new, and replaced with a 3.9 which I saw.
It had this heat issue from 'new', and never having run a 4-barrel manifold before - always SUs - I assumed it was something to do with that, and put the 82 stat in there to compensate.

With the 82 stat it never lost water, but not much fun in winter.

On startup the (manual) choke is fiddly, too fast too slow, so it's hard to say whether it's rough.

We ran about 15 miles yesterday, some traffic, temp hovered below H, fan never came on.

Coolant is new and has no smell, yet. I'll get some block tester. We don't seem to use the strips over here, they sell the fluid instead.
[www.ebay.co.uk]

Onwards...

Ivor

The leak tester has not yet arrived.

Out with the stat, cut the jiggle pin and drill the hole to 11/64", then drill another 11/64" hole on the opposite side.

Now, it seems to run with the temp just above the half mark. Only did five miles but one of those was up a 1:4 hill so it got fairly warmed up.
Try again on a warmer day.


Ivor

So you made yourself a high flow thermostat. Very clever!