12 replies to this topic

[timmins]

I suspect I may have a blown head gasket. Pretty annoying, since I got the car three months ago I've used well over 100 latex gloves!

The car (1098 Clubman) runs fine and doesn't overheat, even sitting in traffic in 90 degree weather. A few times recently, I've noticed coolant dripping out under the car, but only immediately after the engine is switched off.

I suspected the water pump, since it has been noisy for some time, but it still happens.

My questions are:
(1) Is this very likely to be a head gasket fault (I don't want to strip it down unless it definitely is)
(2) I don't have a compression tester, so is there any other simple way of finding out?

Incidentally, there is a periodic 'hiccup' when idling. It'll idle for six seconds, bounce down a couple of hundred RPM, then idle for six seconds etc. Could this be related? I have no vacuum leak, but the exhaust is blowing slightly.

Many thanks!
Tim

[lawnmowercrap]

Have you replaced the water pump?

Start it and remove the radiator cap and rev it. You should see the water inside gushing about and most of the time it will overflow. If not then your water pump is gone.

Mine in my clubman used to be fine on long journeys but when I was in Mc Donalds drivethrough it would overheat so id have to turn it off. That turned out to be the water pump impellor had fallen clean off...

Get it fixed soon, else if the headgasket isnt gone, it will be soon.


Dont look for mayo in the cap. Very poor way of diagnosing a head gasket fault. to be honest a compression tester is the easiest way to do it. Halfords sell them very cheap. If not, get a 'sniff tester' this checks for exhaust gasses in the coolant, wont work if its blown between 2 cylinders...


Lee

Edited by lawnmowercrap, 07 April 2010 - 06:44 AM.

[MRA]

If its blown between 2 cylinders the compression tester should pick that up, however I suspect that you could have an ignition fault, this sounds like timing is either not correct or is moving around due to worn parts..... can chain, dizzy spindle etc..

[timmins]

Forgot to mention that I've changed the pump already, so it's not that.

So it appears that when I stop the engine after a long run, the water immediately starts to boil. I expect that's normal, because it's not circulating anymore. But why does it bubble out the overflow pipe? And why isn't the water that comes out boiling hot? Could the radiator cap have anything to do with it?

I will attempt to do a compression test, and let you know what I find.

Thanks,
Tim

[leepol83]

Forgot to mention that I've changed the pump already, so it's not that.

So it appears that when I stop the engine after a long run, the water immediately starts to boil. I expect that's normal, because it's not circulating anymore. But why does it bubble out the overflow pipe? And why isn't the water that comes out boiling hot? Could the radiator cap have anything to do with it?

I will attempt to do a compression test, and let you know what I find.

Thanks,
Tim

Maby a temperature gauge fault could be overheating just not showing it on the gauge.
Lee.....

[BoboGib]

could it not just be an old rad cap that is past its best? Have you found yourself frequently topping the water up since you have changed the pump?

[dklawson]

Tim, you may not have a problem at all. What you did not mention in your previous posts is whether you are re-filling the radiator after each occurrence and if so, are you filling it all the way to the top.

In our climate, a completely full radiator (up to the base of the radiator filler neck) will burp out a fair amount of water after a long run at temperature. If you check the level and find the coolant is down a bit (maybe 1/2" below the filler neck opening but still covering the core) leave it, don't top it up. You should find that on subsequent runs there is no more water coming out of the radiator. If you keep filling it each time you stop... it will keep discharging a bit of coolant each time. Alternatively you could rig up an overflow bottle to collect the fluid. With the right cap the fluid will be sucked back in like on a modern car.

I know you said you put in a new pump. However, there is the high-flow GWP134 pump with cast impeller that may help if you determine that you really do have an overheating problem.

My car's idle RPM will drift as much as 200 RPM and it doesn't want to idle smoothly on a hot restart. Following a hot restart I have to drive about 1/4 mile before the car will return to a normal idle RPM which in my case is around 1000 RPM.

As for checking for the blown head gasket, a compression tester is helpful but on some engines may not show a blown gasket. On my project Spitfire for example, the compression tester showed even but low compression figures for all 4 cylinders. However, when I put a leak-down tester on the engine I found that there is some kind of leak into the water jacket on one of the cylinders, leaky valves on two more, and bad ring blow-by on all. The compression tested couldn't tell me any of that... only that the compression was low.

[timmins]

Thanks for the suggestions folks.

Tim, you may not have a problem at all. What you did not mention in your previous posts is whether you are re-filling the radiator after each occurrence and if so, are you filling it all the way to the top.

I was thinking along the same lines, so I have been careful not to overfill the radiator... when cold, I'm only covering the core by a few mm. It's loosing enough fluid to bring the level down below the core.

I know you said you put in a new pump. However, there is the high-flow GWP134 pump with cast impeller that may help if you determine that you really do have an overheating problem.

I'm really not convinced it's overheating, the temperature sits in the middle of the gauge, and the water is only chucked out after the engine is swiched off. Are you suggesting that the high-flow pump may be the solution?

My car's idle RPM will drift as much as 200 RPM and it doesn't want to idle smoothly on a hot restart. Following a hot restart I have to drive about 1/4 mile before the car will return to a normal idle RPM which in my case is around 1000 RPM.

I'm not too concerned about this issue, I was wondering if the RPM drop maybe pointed to a compression problem. But I suspect the timing gear or distributor, as suggested by MRA Minis.

As for checking for the blown head gasket, a compression tester is helpful but on some engines may not show a blown gasket. On my project Spitfire for example, the compression tester showed even but low compression figures for all 4 cylinders. However, when I put a leak-down tester on the engine I found that there is some kind of leak into the water jacket on one of the cylinders, leaky valves on two more, and bad ring blow-by on all. The compression tested couldn't tell me any of that... only that the compression was low.

That was my thought. I ordered a gasket set from Moss today, along with a rad cap (not that I really think that's the issue!).

This car is testing me! I had four Austin Allegros over a period of ten years... in the last three months I've had more issues with this Mini than all the Allegros put together

[timmins]

could it not just be an old rad cap that is past its best? Have you found yourself frequently topping the water up since you have changed the pump?

I have been topping it up frequently, and I ordered a cap to be on the safe side! I'm still not sure how the radiator cap could cause this issue though.

[dklawson]

The new cap may help in two ways. I don't remember the ratio, but for each PSI higher a cap is rated you move the boiling point of the cooling up by a certain number of degrees. So the first benefit of a new cap with a higher release pressure is that you won't boil over at relatively low temperatures. If the coolant is still at "normal" temperature, the higher release pressure cap may help in a different way. When you switch off the engine and coolant flow stops, if the cooling jacket is extra hot and the temperature starts to rise, a higher pressure cap will release "later" than a lower pressure cap. In short, you will potentially keep more of the fluid in place.

As Martin said, you could adjust your timing a bit to see if this improves things also (both temperature and stabilizing the idle speed).

In answer to your direct question, I was only suggesting that the GWP134 pump may allow better coolant flow so you have less chance that there are any hot spots in the cooling jacket that may contribute to boiling over when you switch off.

It sounds like you are already doing what I would have done with the refill level. I'm afraid I don't have much more to offer.

[timmins]

Just a follow up for searchers - the replacement cap (13 PSI ffrom Moss) fixed the problem. No more wee-wees!

[BoboGib]

Glad you got it sorted.

[dklawson]

Thanks for the follow up Tim. I'm glad you got the issue resolved.

by the way, May 15th is the MG Car Club Show at North Hills in Raleigh. I hope you get a chance to come by and/or show your car. It's a short gathering. The event starts about 9:00 a.m. and things wrap up a little after 3:00 p.m.