Hissing noise from under carbs???

[Roy S]

After much searching I found what I wanted, this being a late (77) white manual Stag. Needs a respray but engine was rebuilt about 1000 miles ago by HRS and the body is in great condition. Picked it up drove it 50 odd miles home with temp needle about 1/4 up the scale and it stayed there the complete journey. Over the next few days noticed the expansion bottle was low so topped up to half way with water/antifreze mixture.

Now the questions......:-/
After 2 weeks away on holiday checked water was still at same level and took the car for a spin, 3 miles from home noticed the temp was in the middle??. Carried on a little and it started to go a little higher quick U turn and headed home, one slight miss but that was all. The needle never made it to the red and pulled up in the drive to hear the expansion bottle gurgling and spitting moments after switching off.

After the gurgling stopped I could hear a low hissing sound like escaping steam/water and this was from the top of the engine and seems louder from the back of the carbs but in the center of the engine. I've looked under and around the inlet manifold and no water and no steam but still hissing, rad pipes were also hot and under pressure. Left it for 30 minutes, hissing stopped but again no water dripping out from round the inlet manifold. At this point I'm thinking it must be escaping inside and going into the cylinders so careful turn of the key, nothing out of the ordinary and she started and idled as before. I switched it off and again tried to see if I could see any hose dripping water but nothing.

So what the hell was it, the car never got this hot before, I can't check the water level until tomorrow as it's still hot but you can see water has been blown out of the expansion bottle. I'm thinking the worse that it's blown a head gasket but the hissing was from the top of the engine and the oil is still clean. I let it idle a little when I originally came home after it had sat for 10 minutes cooling and no vapour was showing from the exhaust.

I'm thinking maybe the stat could have failed and the hissing could be from a pipe tucked near/under the carbs and inlet manifold. Maybe even a cracked inlet manifold or failed manifold gasket.

So a cry of help..... was looking forward to moving from my current 72 MGB into the Stag this week but she's not playing ball. :'(

[Bryan]

Roy, from what i have read and heard from various people, cylinder head gaskets do and will fail. You may well have been unlucky. If there was a  problem before you bought the car you would certainly have noticed it on your journey home. Someone else may want to comment but it still sounds like to me a blown head gasket given that you are pressurising the water bottle. The hissing noise could be from the inner seams of the heads under your carbs. The water so hot that it was coming out as steam and evaporating before it got a chance to lie in the vee between blocks.
The other problem could be a partially jammed thermostat. That is easier to check and something you can remove, check and try the engine again if necessary with it removed. I hope your problem turns out to be a small one. Once you've investigated, please advise us what you find.

[Roy S]

Well opened the expansion cap and the bottle was full, took the rad filler off and that was empty taking about 5 litres of water, not looking good.

Filled up both bottle and rad and kept pumping the top hose to get as much air out as possible and when all filled up started it up and let the engine idle. Ran as smooth as ever and started to look for any leaks as I didn't see any water comming out last night but it was dark.

When a bit of heat/pressure had built up switched it off and listened for the hissing sound again but nothing. Started up again and let the temp rise to 1/4 way as it normally did.

Found water leaking out of base of expansion bottle and the hose clip was rotted through and so replaced this. Started again but the bottle is leaking again from the base of where the cap fits so the expansion bottle looks shot.

Will order up a new bottle tomorrow and 20lb cap plus a new 82 stat and sender as well. When I fit the new expansion bottle and the new cap I'll get the car hot and the coolant under pressure as I still can't hear this hissing like last night. Did find a small puddle of water under the inlet manifold at the back of the engine. Cleaned this up but no more seen and I can't see where it could have come from.

Still hope the water is leaking from one of the pipes or joints in and around the inlet manifold but with the current expansion bottle fitted its not really building up the same pressure as before.

Will post an update on the results.

[Bryan]

When filling your coolant system ensure the heater controls are set to hot to ensure you fill the matrix properly and the correct amount of coolant has been poured into the engine ensuring no air locks or lack of coolant. Still don't like the sound of the hissing and the bottle being full means it has been pressurised out of engine so something is wrong. Have you tried checking the thermostat yet. It could be that which is giving you the pressurisation problems. It's an easy check and you might save further more expensive problems. Do this while you are waiting on your new bottle.

[Roy S]

I have the controls on hot, so I think it's filling up OK but as I didn't drain all the coolant out I don't know just how much was still in there. I'm ordering a new stat with the other parts today anyway just to be on the safe side. Mind you when I was running it last night it only heated up to where it would go to normally which was 1/4 of the way up the scale. At least with a new stat and a new sender I can be a little happier the engine is running at the correct temperature, I'll also check the temp gauge by shorting the sender wire to ground to make sure it reads all the way accross the scale. At least with all that done then what ever the gauge reads after that I'll know it is the normal running temp for the car. Fingers crossed...... :-/

[nibby]

Sorry to hear of your problems Roy S it seems to be a bit to "all of  a sudden" to be a head gasket, not that im the best mechanic in the world but is the water pump working alright and of course your stat and expansion bottle like you and Bryan have mentioned need close scrutiny.
My expansion bottle is not functioning properly at the moment because the brass sleeve around the top moves when i screw the pressure cap back down and does not seal properly.
Hopefully your problem will be minor.
nibby

[Roy S]

I have a new one on order, the current one leaks like your one from the metal sleeve the cap screws down on. Also have ordered new cap & stat so when these are fitted it should pressure the system up again and I can get back to tracing where this original hissing noise was coming from. I think the start of the over heating was the jubilee clip to the bottom of the expansion tank finally failing, the muck & rust under the bottle shows it must have been leaking for a while before I bought the car. The hissing noise was I think the final part of the pressure leaking somewhere from a pipe near the inlet manifold or even the manifold itself possibly. With the leaky bottle in at the moment it can't get the water under enough pressure to do it again. As you can tell I'm trying to convince myself the head gasket will be OK  :-/

[Bryan]

You are doing the right thing looking at the least expensive and easy to fix items first. Your head gaskets may well be ok. I don't understand the leaking at the cap.  Without pressurisation water should n't get that far up the container as any coolant enters and exits at the bottom. The MkII expansion tank hose from the radiator connects at the botom of the tank. The MKI was at the top so in that case understandable but you have a MKII. I am still concerned about the pressurisation problem. For the sake of a gasket - try the thermostat. I hope also your problem turns out to be a minor one. All the best.

[Bryan]

Sorry to add to your possible misery but i have just re - read your first message and you mention a miss. This can be indicative of water getting into a cylinder. I hope not the case but....... Don't mean to worry you but it just could be that the coolant pressurising has found weaknesses in your system that is leading you down the wrong path. OK they need to be resolved but may not be the root cause. Again - good luck.

[Roy S]

OK so today I fitted the new expansion bottle and new cap plus replaced the pipe and clips that connects this to the rad. I wanted to be sure I'd stopped all the leaks etc before replacing the stat. Started up and let the car warm up, kept looking for water under the inlet manifold and this didn't appear until the car was warm and the top rad hose was getting hot so it happens after the stat open it seems.

Nothing else for it but to remove the carbs and inlet manifold to see if I could trace where this leak was. I hopped that I could get the inlet manifold off fast enough to see where the water puddle at the rear of the engine under the manifold was coming from. But the manifold was a real pain to get off and some last traces of water in the manifold spilling out when I finally got this off ruined any chance off tracing the leak back.

All the pipes seem ok and the other suspect was the water pump gasket but this again seems fine. I was going to replace this gasket as well but I this I'll leave this alone.

So with the inlet ports plugged I've scrapped off all the old gasket and will order some spares tomorrow. Question I have is should I use additional sealant on these gaskets and if so what type. It's not the sort of thing I want to have to repeat so would like to get a good seal first time.

[Bryan]

If surfaces are good and you torque down to correct setting the proper gasket should be sufficient. A smear of liquid gasket won't hurt i guess. Do you need info on  torque settings? If so let me know and i can source in my manuals.

[Roy S]

The settings would help, I found one or two of the bolts too easy to remove and this might have helped the gasket fail. I'm assuming that this is where the water was coming from, there was no way I could see this at the time. It would explain the hissing noise and if the water was being lost because of the expansion bottle connection failing then the top of the engine would start to boil up and the pressure would increase. I'm hopeful the head gaskets that were fitted about 1000 miles ago (the thick type) held out.

Now the next question is how do you torque down some of the bolts as there is just enough room for a spanner let alone a socket and torque wrench.

[Tim Bancroft]

As you are tightening bolts, studs and nuts that are into aluminium the torques settings will not be that high, therefore a good spanner will be sufficient.

[Andrew Lacey]

Roy,
Thanks for your email, when our heads go back together, we will be using a silicone type sealer on the inlet manifold in addition to new gaskets. this is being done as a precautionary measure. Have your heads been machined in the past? as sometimes it can effect the clearances when put back together, this is one of the reasons they use an extra thick gasket. I see you already have extra thick gaskets on your head. Hopfully your head gaskets have not failed. Also check the torque on the head it should be 55lb it is advisable when the heads have been done to check after about 500 miles. There is also a sequence order to torque the nuts down.

Let us know how you get on.

Andrew

[Roy S]

OK thanks, I've ordered gaskets and sealing compound from James Paddock, they recommended the sealant from their experience with water leaks from the inlet manifold. They also had two gasket types with the more expensive one I ordered being what they felt was a better cut.

I'll also re-torque the head again (thanks Andrew) while I'm at it.

So I'm doing all I can and I hope the car appreciates all of this and plays ball.........

[nibby]

Roy i found the best inlet manifold gaskets were payen ones with a little bit of welseal on them as recomended by Tony Hart. Also have a helicoil set handy if my experiences are anything to go by.

[Roy S]

I'll wait and see what turns up then, I ordered the ones they said were the better quality and the sealant was "as used" by the company that did their engine rebuilds.

[Andrew Lacey]

We also ordered our gaskets last week from James paddock, they are always very helpful and if you  want something quick, we have found most things we have ordered are with you the next working day.

Tina

[Roy S]

I've been very impressed with the James Paddock service, the gaskets (Payen) and sealing compound (silicone) arrived today and I only placed the order yesterday lunchtime. Hope to get time to fit them at the weekend, the sun is out but the Stag don't go......... 8)

[Bryan]

No worries like that up here Roy - has been  pouring down for weeks here so i'm carrying on with the titivation until it clears up. Ditto re JP - excellent service also found. Again good luck. If you need torque settings tell me exactly what and i will advise.

[Roy S]

OK all back together but the stat cover bolts when I removed them to fit the new stat had a little too much rust under the bolt head, was worried they might break when tightened up. Quick trip down to the local engineering shop produced two replacements. Fingers crossed when I finally fit it tomorrow, fill it up with water and test.

While I had the chance I checked the head bolts and a couple on each side needed about 1/2 a turn to get them to the correct setting. The gaskets were new about 1,000 miles ago (before I bought the car) so hope this is down to settling down.....

[Roy S]

Well I didn't even get the car started before I found water leaking out. Just by pressuring the rad by pressing the top hose to get any air moved out caused water to leak from the inlet manifold. It's coming out of the front part of the manifold at the top on the RH side of the engine (viewed from drivers seat). There is a small water way at the top and the way the bolts are positioned it does not mean simply tightening down. I'll order up some more gaskets and this time will have to apply more of the sealant. Thought I'd put enough on with a smear on all gaskets sides and the head and manifold. Also I need to check just how well it's sitting before sealant is put on as I can't see how its managed to leak. >:(

[Andrew Lacey]

Hi roy, 

Received your email, from the attached photo you can see what stage we are at. I seem to have fitted mine the same as yours in regards to sealant and gaskets. although I did make sure I bolted the manifold down evenly and slowly in a cross section, ie: corner to corner, tightening each bolt down a bit at a time.  Also be careful as the gaskets can slide out of the way when putting manifold into place.
Our engine will not be started for a couple of weeks so we will be watching your progress. Hopefully ours will be fine.

Good luck

Andrew and Tina

[Roy S]

You must have a different engine, mines a different colour to yours.... ;D

[Andrew Lacey]

Its a woman thing ;)  Wanted blue 8) but could not get it in a hurry