Thoughts or input on thinning 25 year old oil before an oil change.

[Max Headroom]

It may be too late to check but if a freeze plug(s) was cracked or leaking there would be no water in the block down to the level of the crack/leak. The radiator would probably be low too. (letting water back into the engine from lower radiator hose. As Turna says above, the temp gauge is the thing to watch if you crank it.

If the engine is low on water, I wouldn't add any till after letting it run to see if it leaks (and maybe not then). Add water with an internal leak/crack and you can contaminate the oil with water. The water emulsify with the oil, foam up, kill the oil pressure and damage the rod or possibly even the main bearings.

If it's low on water due to bad freeze plugs, sometimes, if the Gods are smiling, you can change some of them while the engine is in the car. It usually means pushing the old one into the block and not being able to get it out but I did it when I was younger and broke. You still don't know about internal cracks but that's what the freeze plugs are supposed to prevent.

 

[OldsDad]

Be Careful!!!!!! A guy that worked for me dumped in some crankcase cleaner. And 2 days later the motor spun a rod bearing

 

[olds307 and 403]

I'm not sure of the exact operation of that style valve, but it stands to reason that it could be replaced with a standard heater control valve in the heater line ($10 part) and installing a standard nipple in the intake port.

I did exactly that, used a universal 3/4" NPT hose nipple from the hardware store. Non A/C Olds V8's had a nipple in place of the valve.

 

[azmusclecar]

I did exactly that, used a universal 3/4" NPT hose nipple from the hardware store. Non A/C Olds V8's had a nipple in place of the valve.

Thanks, my A/C is not working and it is a project down the road. I just wanted to use something to get by in case that A/C Heater Valve is the
culprit that's leaking.........it is probably welded in......😵........from under the intake.........(keep a happy thought)😛

 

[icr242005]

High mileage oils have more cleaning agents and seal conditioners than regular oil. Use HM oil and buy a extra filter. If the engine is real bad I’ve seen them plug up the filter after 200 hundred miles. If u r dead set on using something, use ATF. The viscosity is close to engine oils. Using other cleaners WILL reduce the viscosity and change the chemistry oil the oil.

 

[84 El Camino 231]

Someone mentioned above to have a look under the valve covers before starting up and I agree strongly! I've fond the gritty caked on substances that come from there both ways, before and after... It's best to find it before, especially before it makes it onto the oiling system. If nothing found, then confidence is much higher!