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Old 08-02-2013, 05:16 PM   #1
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Default radiator pressure test

98 GP 3800 (non sc).

On a warm engine (off for about 1.5 hrs) Is it normal to have about 4 lb pressure drop on a radiator pressure test over 30 minutes? Unable to find any kind of test standard. Thanks
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Old 08-02-2013, 05:22 PM   #2
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I don't see why not. As the temp drops, the coolant contracts and reduces pressure in the system.
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Old 08-03-2013, 03:04 PM   #3
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Follow up on pressure issue.
I took the radiator pressure tester and checked pressure first thing this morning and only lost 1 lb during 35 minutes. I ran it to 15lbs. Great no leaks! I also tested the new 16 lb radiator cap and it passed. Here is the but... I put the radiator cap on the radiator and I do not get pressure buildup during warm up and while engine is hot. So, I put the radiator pressure tester back on the radiator and put 7 lbs pressure on it while engine was running. It held pressure. I then hooked up my scan tool and monitored the temp while engine was running. As expected, as temp climbed and dropped so did the pressure readings, ok. I'm not getting any pressure fluctuations while running so I know there is no bad head gaskets. Conclusion: I going to look at the seat of the radiator tube for ang bad spots as for some odd reason the cap isn't holding pressure but using the tester does. Also, I noticed the testor fits a lot tighter. Probably looking at a new rad. Also, found I don't have low speed fan coming on. Only get both fans working with AC on as you should so I'm going to t-shoot the fan issue first starting with the relay(*) ckt and go from there. Let you know what turns up.
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Old 08-03-2013, 03:51 PM   #4
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Last I knew, the low speed fan turns on at 212 and high speed on at 226.
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Old 08-04-2013, 02:51 PM   #5
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Mike

I noticed on my scan tool that when the temp got to 216 F, my fans had still not come on and I was leary of letting it get higher so I turned AC on and both fans came on low speed as they should. I'm still digging into it. I did the relay tests on all three relays and they are good. I also did the jumper tests on all three relay sockets and the fans operated as the tests said they should on both low and high speeds. How hot do you think it should get in reality for the fans to activate either low and high speeds. I know what the book theory says but I wonder about real time?

Also, do you know of any tried and true computer software programs that I can use to scan and even reprogram my pcm more through like the shops have?
I do not want to try just anything out there for obvious reasons.

By the way, I do have a electronics and electrical education so digging into these things is not difficult for me.

Thanks Gary
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Old 08-04-2013, 04:22 PM   #6
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If I was testing, I would usually give it until 230* before declaring the test a failure, especially if you know that firing the A/C turns on the fans reliably. Does your scanner tell you if the fans are being commanded on?

Keep in mind, these engines are cast iron, and can take a lot. I don't worry about damage until 250* (idiot light is on at 255* usually), and many have gotten away with 280*. Of course, however, your mileage may vary.
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Old 08-04-2013, 04:25 PM   #7
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You may also want to try a different brand of cap. I got tired of replacing the autozone caps every 6 months due to leaking, put a unit from car quest on there, and not only did it feel tighter going on, no problems yet. If there is a problem with the neck of the radiator, you should be able to spot it.
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Old 08-04-2013, 06:37 PM   #8
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Agree with rjolly, I'd not declare the test a failure just yet, I've heard fan speeds are 216 for the low speed fan, and 228 for the high speed fan, I'd not expect the fan to come on the second it hits that temperature, I'd give it a degree or two past the programed turn on speeds.

If you want something to change the fan turn on speeds you could get HPTuners, it will run you around 500.00.
Even with knowledge of electronics, and electrical, I'd still suggest finding something to read up on tuning, before actually trying to change PCM parameters.
Our motors run more efficiently at the temps they normally reach, which is why the fans do not come on sooner.
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Old 08-04-2013, 09:23 PM   #9
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Thanks for feedback

No I do not have fan on comand capabilities with my unit. I do have limited live data feeds and DTC capabilitie for the trans. Knowing what I know now, I would have saved my money and added some to it to get a HPTuner. I'm glad I got cast iron engine. I keep hearing the problems with aluminum when over heated. BTW, engine is finally holding normal pressure on its own. I agree with rjolly87 about trying a different rad cap as I haven't done anything to it and now it'* holding pressure. Also cap doesn't feel tight enough to me from past experience.

Also, WilliamE, On the HPTuner, I agree with you about reading up on tuning. Although I program PLCs and VFDs at work, you do have to be cautious and do not make drastic changes as the results can be horrible. Obvious, I do not want to damage motor. I'll research some sites and forums and find out what worked and did not work for others with the 3800 and procede cautiously.
OH. almost forgot, came across a thread at another site concerning 97-99 yrs cooling fans and it said there was a bug in the factory program and it was causing fan issues. As a result, a updated file came out correcting it. I'm going to investigate this a little futher to be sure this is true.
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