# VRT overpressure in coolant system question.



## UrSeRiOuS (Mar 19, 2005)

A few weeks ago I blew my Samco upper radiator hose while under boost (I have the mbc at 20PSI) pulling through 4th. I replaced it with a stock VR6 upper radiator hose. Since then it seems even after light driving my coolant hose will get very hard to squeeze and swell. I'm convinced it isn't normal and haven't many clues to go by. I believe something is causing this pressure and it isn't releasing it from the cap.

The other issue I am noticing lately is my wideband A/F gauge will intermittently show a hiccup while at idle. It will go from reading approx 14.7 to into the low 20s and then correct itself. The correction can take almost a minute at times.

What we know so far is the coolant is not contaminated, I'm not overheating or losing coolant, no unusual exhaust smell or color, and no loss of power.

A little about my car:

1992 SLC with a built OBDII VR6, Garret GT3582R, 8.5:1 c/r, last month dynoed 420whp @ 20PSI, 630cc fueling, ProMAF, UM chip.

Has anyone experienced this?


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## aguyinpa81 (Oct 28, 2004)

The car also reads rich as well at idle after coolant pressure gets high 12.0-13.0afr holds at 1k rpm. When the car idles normal 14's it's at 800rpm. When it does the lean idle it is under 1k rpm but stumbling and sometimes bouncing. I have already cleaned the TB and readapted. symptoms start at full coolant temp. Makes sense. That's when there is the most pressure. We did find out that once it starts doing the 12.0-13.0afr at idle we can counteract it immediately by opening the cap enough to release all the coolant pressure from the system. Hopefully someone out there has some first hand exp on this and can chime in. We do have vag com and can do logs if that can help. :beer:


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## masterqaz (Oct 5, 2007)

Is the engine cts reading properly? Id try a different cap as well. Have you actually checked the cooling system pressure?


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## UrSeRiOuS (Mar 19, 2005)

The CTS is good and tried a different cap. We are trying to locate a kit to properly check the coolant pressure. Today we rebled the system the correct way. :banghead: I felt we should do this again after releasing the pressure while it was hot and running earlier today. That may have created some air in the system. After the bleed I couldn't drive it much with traffic and the rain so tomorrow i'll see what happens.


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## aguyinpa81 (Oct 28, 2004)

I rebled it again this morning with it ice cold. Cap off, idle up to temp while massaging rad hose and doing random 2500 rpm revs. Drove it back home and did some moderate boosting on the way. 8 miles of driving and sure enough the hose is pretty damn stiff yet again. Never overheats though. I guess thats a good thing.


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## aguyinpa81 (Oct 28, 2004)

Simple way to test if a radiator is clogged?


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## 'dubber (Jun 15, 2004)

UrSeRiOuS said:


> ... my coolant hose will get very hard to squeeze and swell. I'm convinced it isn't normal and haven't many clues to go by. I believe something is causing this pressure and it isn't releasing it from the cap.
> 
> The other issue I am noticing lately is my wideband A/F gauge will intermittently show a hiccup while at idle. It will go from reading approx 14.7 to into the low 20s and then correct itself. The correction can take almost a minute
> 
> Has anyone experienced this?


The coolant hose expanding and firming up is normal, the afr reading, well, you could compare it to the narrowband output or correction when it is happening to see if you have a bad readout or an actual fuel or ignition issue.


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## GingerH8r (Aug 16, 2010)

Sorry to say, but it sounds like Head Gasket failure.


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## masterqaz (Oct 5, 2007)

GingerH8r said:


> Sorry to say, but it sounds like Head Gasket failure.


See I was thinking blowing boost into the cooling system which would make sense to what your saying. Would think that would pop the cap though. That hose is a weak point, Ive blown several of them myself. Its the feed to the heatercore so its feeding into a somewhat restrictive part of the cooling system.


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## UrSeRiOuS (Mar 19, 2005)

Yes I was thinking maybe the headgasket, but it still hasn't convinced me yet. No coolant loss, no smoke, no fluid contamination, and only random issues at idle. Boost pressure would have to somehow be pushing into my coolant system and then not allowing coolant to get into the combustion? Idk, while driving it seems ok. Is 20PSI really pushing it? I didn't think so. 

Only because I blew a Samco hose while boosting throughout 4th gear do I believe what I am seeing is not normal hose behavior. This ofcourse is on the 2nd upper coolant hose now.

I'd love to check the coolant pressure at the expansion tank, but it wouldn't matter. Pressure wouldn't build up if I idled my car all day. It has to be driven. I have no way to do this while driving.

The A/F is perfect while driving. At WOT it is about 11s and low 12s. I was just assuming my idle A/F hiccup is related to this new coolant pressure issue. They seemed to have happened at the same time.

Thanks for the input. :beer:


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## GinsterMan98 (May 19, 2008)

*FV-QR*

When is the last time you put a water pump in it?


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## UrSeRiOuS (Mar 19, 2005)

Less then 10k ago when I did the build.


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## sdezego (Apr 23, 2004)

GingerH8r said:


> Sorry to say, but it sounds like Head Gasket failure.


^ This


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## Prof315 (Jan 5, 2009)

sdezego said:


> ^ This


x2


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## masterqaz (Oct 5, 2007)

blew that upper hose today on my car


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## UrSeRiOuS (Mar 19, 2005)

Yay a head gasket. :beer: This was my initial conclusion. Are you guys saying this because it is your educated guess or do you have first hand experience of this? Also what headgaskets are the best? I used a MKIV headgasket for my build. I dont think cometic makes one. VRs get no love.


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## GingerH8r (Aug 16, 2010)

First hand experience with the 1.6TD I had.
Except mine was pretty obvious after losing a bunch of coolant and white smoke. Just had a friend blow up his DSM's HG as well this weekend. if your taking it on, just be sure you clean the crap out of everything before you reassemble.


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## UrSeRiOuS (Mar 19, 2005)

I'm missing the obvious part. :banghead:


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## masterqaz (Oct 5, 2007)

Replace the hose and run it till it blows again. The problem may be more obvious at that point.


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## UrSeRiOuS (Mar 19, 2005)

Yep, that is what I'm doing for now. I'll keep those interested updated. :beer:


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