Hey folks,

Looking for advice to diagnose and resolve this issue that's been bugging me for a long time.

I'm on the Gold Coast and run a 1275 with a Dellorto and pulsar dizzy. Std radiator with an overflow, no oil cooler, ball bearing + spring oil pressure sensor, smiths gauges.

On warm days (prob >20C), after letting the car warm up and heading out on a moderate drive (say > 20min on the move), I'll find myself at some traffic lights and then things get a bit weird. The temp gauge will creep up just a bit from the 1/2 way mark that it usually sits at when moving, and maybe go up to 2/3. The oil pressure will dip a from ~70 to about 50. I'll find that pushing on the clutch pedal will cause the revs to drop.

After I get moving the temp drops back to the 1/2 way point but interestingly the oil pressure never really recovers. It'all stay around 50 on run.

After a few more stops at lights the oil pressure / clutchproblem will get progressively worse. Temps start to get closer to the 3/4 point (never to the H though) and the oil pressure will dip to ~25 when not moving. At this point it gets to be tricky shifting into 1st and getting moving. I'll need to rest a foot on the gas to ensure the engine doesn't stall when I hit the clutch.

I'M wondering whether to start with coolant, radiator, engine temps or look the oil pressure side of things?

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dwightgunning.com

So I decided to see if I could learn anything about the coolant temps and the gauges... so went out and bought a digital thermometer.

I started up the car from cold without the radiator cap on and dropped in the thermometer. It's a sultry 27C day today.

The temp gauge sat still on about 25% and the thermometer on about ~50C for quite a while... then I guess the thermostat opened up... the temp gauge moved up to just below 1/2 way, and the thermometer crept up to 79-80C. I let it run like that for another 5min or so but everything was pretty stable so I got bored and turned the engine of. Couple photos attached.

To me that looks like the temperature gauge is working correctly. Am I right to believe it's fine if the gauge goes up above 1/2 to somewhere between 2/3 - 3/4? That seems like hotter than ideal but not hot enough to do any damage?

Assuming the temperature isn't a major issue. I'm really stumped about why the oil pressure goes drops away so much... that's what really concerns me most.

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dwightgunning.com

I hope the thrust washers in your engine have not been installed the wrong way.

The temp probs you describe sound like the symptoms my car had. Even though my old brass radiator was flushed and flowed well, changing it with a cheapo aluminium one has improved the temps somewhat. Where it used to peak just below H, it now only reaches 3/4 max whilst sitting at the lights. My next plan of attack is to change the pulley to a smaller one, and possibly change the 88 degree thermostat to a 74 degree one.

Forgot to mention my old brass radiator is a 3 core 50mm thick. New alu is 2 core 40mm core width. I reckon 50mm alu one would be even better...

There's not really any way to measure flow while the radiators still in the car is there?

You're thinking the coolant temp is the source of the oil pressure dipping and clutch problem? I've been running Penrite HPR30 in it.

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dwightgunning.com

Are there any other symptoms or other ways to diagnose this? Sounds sketchy!

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dwightgunning.com

I had my rad out when it was flushed.

While you're there, best change the water pump too if age/condition is unknown.

If the radiator was blocked to any great amount the temp would go even higher. You say the gears get harder as temp goes up, this could be a few different things, one may be it's poor or wrong oil affecting syncros, two, the clutch is acting up as it gets hot, causing drag. When its hot, what happens when you select reverse? Crunching?
79C is fine, a long way from boiling. I wouldn't be concerned about that, even the oil pressures not that bad at idle. What oil are you using?
So far as idling slow when hot it could be mixtures off.

To me the temp actually seems okay - I would say on an accurate reading gauge anywhere between 1/2 and 3/4 is a good temp.

In terms of getting gears and oil pressure - What type of oil are you using? The wrong type of oil could be a factor with this.

weak idle could possibly be a mixture issue? - is the carb tuned?

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I wish I had some sort of witty quote in my signature

The gear changes definitely get more difficult and crunchy after it gets hotter. That's my main concern with it all really.... if I didn't have to nurse the gear changes and pay attention so I don't stall it when selecting 1st to take off at the traffic lights, I wouldn't be bothered by the temp gauge showing 3/4.

Before I started thinking about the coolant temp, my gut instinct was that the oil is getting too hot, thinning out, and then causing the problem. I had started to look at oil coolers but then saw another thread where they're really not necessary for a road car.

I've been running Penrite HPR30 in it at the moment. I did try a couple alternatives a few years back: a Penrite alternative (can't remember which rating) and some flashy synthetic Castrol magnatec stuff. I didn't like either... both seemed to be worse at the higher temps.

The carb is a Dellorto so it's really just the idle mix that I can tweak. I selected the jets based on spec and the "how to build and power tune..." book. I'd like to get the car on dyno and properly jetted but I figured I want to sort out this issue first.

The idle is fine when cold. Perhaps I should try adjusting it once it's hot and showing the problem? Although given it's idling slower as it gets hotter, that seems like I'll end up with a very fast cold idle. I'll give that a go anyway.

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