Hi all. I wonder if anyone could please help me with this. It's a 2001 4WD Blazer (UK spec).

The car has been losing coolant and I've traced at least some of the loss to a leaking heater core (wet carpets). Until I get chance to do the job properly I thought I'd bypass the heater to stop the leak. So... I've disconnected the two heater hoses (one 3/4" and the other 5/8") and effectively joined them together so that the coolant still circulates in the pipes but misses out the heater. So I've basically joined the heater pipe that comes comes out of the block behind the thermostat to the other one that comes out of the block near the water pump.

So far so good and all seemed fine when I started the car and took it for a drive round the block. When I got back I noticed that the temperature gauge was reading high and the large radiator pipe coming off the thermostat housing was still cold, as if the stat hadn't opened. I let the car idle for a couple of minutes and after a while it seemed that the thermostat had begun to open. HOWEVER... I was suddenly nearly swept away as coolant POURED out from somewhere under the car.

I let the car cool down for the rest of the day and then went to refill it, expecting a waterfall from somewhere under the car, but nothing happened. I've since started the car and it isn't leaking (although I haven't had it up to temperature yet.

Can anyone explain what's happening? Is connecting the two heater hoses together a stupid thing to do? Why did it spew it's coolant out like that?

Any advice would be appreciated.

Cheers,
Lee

 

Hi Lee,

Connecting the heater hoses together is what I would have done and I believe is something I've heard of others here doing.

Have you checked all of your radiator hoses and their clamps? Have you made a visual inspection of the radiator?

Perhaps the cooling system is leaking only when it us under pressure?

Perhaps someone else has had a similar set of symptoms.

 

Hi Christine.

Thank you for your quick reply. I'm glad to hear that connecting the two hoses together is something that others would consider, too.

The car has been neglected by previous owners and old Dex-Cool is probably responsible for clogging up the heater core. It's probably clogged other things up too. Now that the heater has been bypassed the extra pressure in the system might have dislodged some of the crud and could even have clogged up the thermostat (?). I might take it out and check it as it doesn't seem to be opening when it should. I'm still not sure where the 'tsunami' came from, but it seemed to be pressure-related, almost as if an overflow valve had suddenly opened. At first I thought it might be a core plug, but hopefully I'm wrong. I'll check all the heater hoses as you suggest.

Cheers,
Lee

 

You are welcome!

That sudden gush of water is an odd symptom. The reason I suggested checking the hose clamps was I was trying to think of a failure mechanism that was pressure related. What I imagined was a hose clamp loose enough so that if enough pressure built up, coolant could get out.

But the I realized that perhaps the radiator cap might be the culprit and when it suddenly opened, coolant came out of the hose to the coolant reservoir.

I'm afraid that is the best I can come up with. My ideas seem nutty to me but perhaps they might give you some ideas.

It does sound like you might need to replace the thermostat.

 

You might want to look into your lower intake manifold gasket. Very common problem on these engines, and if it had never been changed before they will let go without notice and can result in exactly what you described happening. Plenty of info on this site about this problem.

As for bypassing the heater core, I did it for a few months when mine started leaking with no problems whatsoever. Well, there was one problem. At the time the heater core went I was living in a small apartment with nowhere to work on my Blazer. So, I had to pay a pretty good chunk of change to have it changed out before I went hunting.

 

Hi all. Thanks for your comments and advice. I've been tinkering with the car and the problems have only got worse :-( The car starts and drives fine but now overheats after a few miles. We're having hot weather here at the moment (well, hot for Britain anyway :-) ) and yesterday I had to stop a couple of times as the car was beginning to boil over. Not sure if it's a blocked radiator or if the inlet manifold gasket has gone. Connecting the two heater hoses together has definitely made any underlying problems worse.

I removed and checked the thermostat after the incident the other day - it was a bit clogged so I cleaned it and it worked a lot better (a new one is on order). I've also tried to flush out the radiator as much as I can, but I wouldn't be surprised if many of the channels are still blocked with crud. When I turn off the car the radiator only feels hot in places and still cold in others. The oil on the dipstick still looks like oil and doesn't seems to be milky, so I'm hoping that the head gasket is still intact.

If the problem is the radiator then I'm prepared to fix it, but if it's the inlet manifold gasket then I'm not so sure. Is there a definitive way for me to isolate the problem?

Many thanks,
Lee

 

Do you still have coolant loss? If so is it still visibly flowing or a slow loss over time? If so you may want to get some UV dye in that coolant and look for the source if you still can't find it. Also, you can pressurize the system and look for the leak. That's one issue. If its overheating when the system is full that's another issue. You have to make sure that the system is fully bled because some trapped air up top can cause overheating.

If your LIM gaskets are cutting loose you would still be able to run without overheating after a proper fill and bleed until you lose enough coolant to start all over again. You can test the coolant for acid which indicated a head gasket issue as well as observe a pressure gauge in the fill neck while running. Then there is the fan clutch and as you point out, the radiator itself.

George

 

To augment what George suggested, it does sound to me that you very likely have a clogged radiator. But this raises the question of how it got clogged. In the past the original Dexcool coolant had issues with this that have since been fixed. These were associated with air leaks and incompatibility between the older ethylene glycol based coolants. In both cases a brown crud, a bit like mud, would form throughout the engine's coolant passages. I found quite a bit in my truck after a local shop put the wrong coolant into it and required me to replace my radiator and do a flush of the system at home. And then years later, I still saw evidence of it when I had to replace the block heater that was installed in one of the block freeze-plugs.

As for testing, very many of our auto parts stores in the States will have tools that they will loan you. Of these, there are ones that you can install in place of your radiator cap that will allow you to pressurize the system with the engine cool and the engine off. This is a pretty easy and safe test to do, especially if you feel skilled enough to replace a radiator.

But, if you find no leaks, then you likely have some blockages and your engine block and cooling system needs to be flushed. Without a complete flush, the radiator could be clogged once again. This is possible to do at home but I suspect a shop could do it much more thoroughly. And don't forget to check the coolant overflow tank. I found lots of crud up in the corners after it after I flushed my system.

I was also thinking a bit more about your tsunami of coolant. I started to wonder if your coolant loss could have been from the coolant expansion tank's overflow outlet. If there had been a sudden pressurization of the radiator on the side with the radiator cap sufficient to override the spring in the cap, this could have allowed a large inflow of coolant into the expansion tank which could have been filled quickly to overflowing. With the overflow outlet of the expansion tank hose partly down in the engine bay, a loss of coolant form below would be expected. And this mechanism would be consistent with not finding any leaks.

P.S. "LIM" = lower intake manifold. Hopefully you will not have to deal with this. I don't know the years of when the bad ones were used. I'm sure that information is posted in the forum somewhere.

 

Hi George and Christine. Thanks again for your advice.

I think old Dexcool in the system is probably the culprit. I'm not aware of anyone using it over here in the UK, so it's highly likely that at some point in it's life the cooling system has been refilled with 'normal' antifreeze without a proper flush being carried out. A thorough flush and a new radiator might sort it out for now, but I'm fairly sure I'll have to sort out the inlet manifold gaskets in the not-too-distant future if I decide to keep the truck.

Christine, I think you're right about the coolant coming out of the expansion tank - that's what happened yesterday. Twice. Probably didn't do the engine much good to be boiling away like that... :-0

I'll see if I can take the radiator off and get it checked at a local specialist.

All the best,
Lee

 

Sounds like you are getting close to getting at least a proper diagnosis!

As for the LIM gaskets, their replacement is something many of us have done. It is more involved than swapping out a radiator but people here can walk you through it and give advice about what to expect.