NGC, vintage V8 spewing coolant but not overheating....

[brider]

I have a chronic issue with an old Range Rover with the Buick 4.2L clone V8; it continually spews coolant out of the reservoir cap (which is where the system relief calve is), but never overheats, as I would expect if there were a leaking head gasket. No white smoke, starts, runs, & idles just fine.

The only things I can think of that would cause this spewing would be:

A), bad reservoir cap, allowing system to release too early (system/cap is I think a 16 PSI rating?).

Or,

B), exhaust pressure in the system. I had the system checked YEARS ago when this was also happening and it came up neg, I know that means nothing now. But wouldn't there be other symptoms? White smoke? Rough running? Overheating? None of that, purrs like a kitten.

I have a contraption to add VACUUM to the cooling sys, is there something similar to pressurise the sys to see if the cap IS releasing too early? Should I just buy a replacement cap? I did that also years ago with no lasting improvement.

[73 sport]

    If your buick V8 is an aluminum block, it is incompatable with many antifreezes. A goop is formed that plugs up the radiator.

[brider]

I've been running green generic coolant in it for 15 yrs, radiator was re-cored but there wasn't/isn't any evidence of excessive goopiness.

[michaell32]

A weak radiator cap can do that. Also if they gauge just shows red and green or c and h I wouldn't rule out that it's not overheating. Ive seen cars hit 250 and the gauge was just over half way between the c and h. Go off the obd2 scanner if it's newer than 96.

[cliffrod]

A Stant 12270 pressure tester like this kit will test radiator and caps.  It may need an adapter to fit your specific cap.  These are very handy for checking the system for leaks and pressure.  Here’s a link to one on eBay-

https://www.ebay.com/itm/298633056769

Other companies make them.  I’ve always trusted Stant for them when working on my old cars.

Typically, If it spits out coolant but doesn’t run hot, it’s a simple overfill issue.   Sometimes filling it to FULL on the resevioir need to be done when it’s cold, not hot.

[73 sport]

   It is about time you went to a radiator shop and have the core checked out.

[brider]

I'll check out that pressure-tester, thanks.

It's a '93, so no OBDII.

Had the rad re-cored & re-tanked maybe 20k miles ago. I don't think it's an overfilling issue, the coolant will spew out until the reservoir is dry.

[cliffrod]

Caps are simple and relatively cheap, even a good one.   

Will the same thing happen whether parked and idling (like 30-45 min) or while driving for same amount of time?   Electric fan or clutch fan mounts to engine?  Does electric fans and switch work properly or does clutch fan thermally operate as intended?  Is shroud on radiator?  Have you checked actual engine temp with mechanical guage or infrared thermometer?

If all the normal stuff fails, my btdt.  The first car I bought with my own money was an 100% original, mint condition 1967 Ford Mustang.  289, one owner little old lady car.  It was also an explosive overheater, even worse than you describe.  I was bummed & thought I got screwed.  but seller got it on straight trade for some body work on another car for the old couple who never drove this Mustang anymore, so it wasn’t a typical scam.   He said he never drove it and was just selling it.

We did and tried everything for months- redid radiator, different fans, shroud, flushed engine multiple times, pulled heads & valve job, somewhat hoping to find a crack or warp and more..  eventually, when I took radiator to the shop for the third(?) time, the boss sent me home to bring the car to him.  Long story short, he put his pressure washer wand into the empty thermostat housing and blew lots of big chunks of black/brown goo out of the water jacket.  Very educational…

He said it looked like the previous owner had been adding a bottle of stop leak on a regular basis for years, much like you used to add water pump lubricant/milk on a regular basis to keep seals happy.  After all that had already been cleared by me working on it, he figured he got 7-8 bottles worth of stop leak out that day.  Said he had never seen that much come out at once.  Car never ran hot again. 

As mentioned, aluminum block & heads may not play well with some antifreeze.   If it’s gooped up from such a situation, the same approach may clean out the water jacket.

[Fontain25]

I had a very small leak on a head gasket and it did the same thing. To diagnose it my mechanic used a special liquid in a hookah looking device that screws on for radiator cap. The liquid changes color if exhaust gases are present in your coolant. Don't know what it's called, but it helped where other diagnostics didn't detect anything.

[brider]

I had a very small leak on a head gasket and it did the same thing. To diagnose it my mechanic used a special liquid in a hookah looking device that screws on for radiator cap. The liquid changes color if exhaust gases are present in your coolant. Don't know what it's called, but it helped where other diagnostics didn't detect anything.

With all due respect to Cliff & others sharing their experiences with goopiness & radiator deficiencies, this truck has never experienced an overheating condition except when the WP failed or when the upper & Lwr hoses failed. I've driven it 4 hrs straight, much of that on the Mass Pike at 70-75 mph and it has never overheated from normal operation. And as I said, I've had the radiator re-built and replaced the WP & T-stat.

It's tempting to think of the coolant-spewing as overheating, but I know what overheating is, and there are no symptoms of that condition. And the factory guage DOES work, I've seen it move into overheat-zone during the WP & hoses episodes.

As Fontain25 suggests, I think it's time for another exhaust-gas (& pressure) test. A leaky head gasket, regardless of the no-symptoms condition (except the spewing) seems like the most likely culprit.

[cliffrod]

I missed this last post. One of the reasons I like the Stant kit is that it can help diagnose a compression leak (which can include ann exhaust gas leak) into the water jacket.

[Ncdan]

Stuck thermostat.

[rocker59]

Yeah..  My vote is bad radiator cap.  They go bad, and are cheap to replace.