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Discussion Starter #1
92 Daytona, 3L. new rad, new thermostat, 3 yr old heater core, 5 yr old hoses. Water pump and pipes ~10 yrs.

There must be a leak somewhere. It looses coolant pretty quickly. But even sometimes when theres still coolant in the CRS tank, I sometimes boil over after shutting the car off.

I've pressure tested, and (cold) it seems to hold pressure fine. Cap holds ~16 psi, system holds ~16 psi and did so for ~10 minutes. Haven't pressure tested hot though.

I've added UV dye to the system and looked for leaks. I cannot find anything. I'm checking both rad hoses and both heater core hoses. Thermostat housing. Looking on the ground under the car. Nothing shows up while idling to full temp (cycling fan). Nothing at the tailpipe either.

One thing I noticed while UV testing was some bubbles in the CRS tank. I figure this can either be 1) exhaust gases and I have a blown HG, 2) air still purging from the system from the last time the coolant got low, 3) boiling coolant.

To test (1), I got one of those blue-to-yellow chemistry tests to see if there is CO. Cant do it straight at the rad neck because I keep getting coolant burping up and flying out. But, before that, no detection of CO. I also tried letting the gas escape to the CRS and detecting with the test there. Negative, but I did pay more attention to the bubbles. Today, appearing for just the 1-2 seconds before the fan kicks on. I timed the cycle too, ~45 s fan, 2.5 min no fan. Letting everything cycle for ~20 minutes did not stop this. So maybe its not (2), but maybe I gotta go longer? I'm not 100% convinced i have a true negative on the test though.

Considering the newness of many of the parts, I think my options are down to head gasket/head, and maybe the waterpump/piping? But I'm having trouble getting any conclusive evidence that either is bad. HG wont fail the chemistry test. Rad hoses get hot, and heatercore blows hot air.

So... What are my next steps here? I'm at my wits end!
 

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The only way you are going to verify a headgasket issue is with a Cylinder Leakdown Test.

Is there any indication of water/coolant in the oil(white/slimy/sludge on the dipstick or oil cap)
Are all 6 spark plugs burning normally, none are different than the others, if a small amount of coolant is entering a cylinder that plug tends to be cleaner than the rest.

Again, the only way to verify a headgasket/waterjacket sealing issue is by performing a Cylinder Leakdown Test.
Since you are not looking for a difference from cylinder to cylinder you do not even need the Leakdown Tester, just connect an air compressor to the test hose from a compression tester.
You still have to have each cylinder at TDC on a compression stroke when testing that cylinder.


 

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Discussion Starter #3
HA I knew you were going to say that. I'm looking into leakdown tests now.

Oil shows no evidence of coolant. Coolant shows no evidence of oil. I havent looked at the plugs yet.

However, what you said about the spark plugs reminded me of something I saw when I replaced my front exhaust manifold last year. When the manifold was off, I could see the exhaust valves. There were different colors. As though different dirtiness. Heres a montage:
270940


Maybe related? Maybe not?
 

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I had a similar issue for 10+ year but fixed it last year.
I ran my car for a few weeks with Prestone Rad flush, and followed up with a week of Thermocure. Of course water flushes before each treatment.
Also watch the hose fittings on new rads as they are undersized for our hoses.....
 

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Discussion Starter #5
Also watch the hose fittings on new rads as they are undersized for our hoses.....
This may actually explain why I have such trouble keeping the hose clamps tight. I kept thinking I'd solved this when I pressure test and find a loose hose clamp. But now I'm sure the clamps are tight and im still loosing coolant.

If the leakdown test shows nothing, I'll give these flushes a try.
 

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Discussion Starter #6
OK so I took the car to a shop today, since I didnt want to invest in all the equipment to do a leakdown test.

They only tested 2 cylinders in the front, but didn't get much leak. However, they did detect some exhaust in the coolant with their emissions probe. But it must be a slow leak, at least when at idle, which is what I had guessed anyway. I think its more severe when hot and/or over 2k rpm.

They also think my valve guide seals are leaking, evidenced by a puff of smoke when I start the car.

So.. I guess my heads are coming off. Is it absurd to want to attempt the valve job myself? I'll still take the heads to a machine shop to check their flatness. Should I be worried about the block too?
 

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Unless the vehicle was severely overheated I highly doubt there will be an issue with the block.
If you are in doubt you can use a straight edge and feeler gauge, no more than .003".

Be careful what you clean the deck surface with, getting small amounts of fine granular particles into the oil pan can result in damaged rod/main bearings.
NO
Roloc Reconditioning Discs.jpg
YES
Roloc Bristle Discs.jpg


If you need/want any service info let me know and I will post it for you.
 
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