coolant blowing back into overflow resevoir

[jonespj]

My 1985 mercruiser 3.7 is blowing anti-freeze into the plastic reservoir before the engine even heats much. I can idle it for a long time and it doesn't do it but when I cruise the coolant blows back and I can hold my finger in the reservoir and the water is not that hot. Could this be a sign the exaust manifold and exaust elbow gasket is bad. I had it apart last year and saw that the manifold was corroded (rather thin walls too). I buffed it and put in new gasket and new elbow but even at the time I wondered if those thin walls that the gasket sets on would seal. Thanks in advance for any help/advice! Paul

 

[stonyloam]

Re: coolant blowing back into overflow resevoir

My 1985 mercruiser 3.7 is blowing anti-freeze into the plastic reservoir before the engine even heats much.

Time to do a compression check and a cooling system pressure check. You can borrow the tools from autozone for free. Sounds like you may have a ad head gasket pressurizing the cooling system. I am not ure that the exhaust has enough backpressure to cause coolant to blow past the pressure cap on the reservoir.

 

[Don S]

Re: coolant blowing back into overflow resevoir

A compression test might not find it, but a leakdown test on each cylinder will. Pressurize each cylinder and watch for bubbles in the coolant reservoir (not the overflow tank). If you see bubbles, you found your problem area.

Another thing. If you fill the reservoir all the way to the top, it will blow some coolant out as the coolant expands from the heat. After seeking it's own level, you shouldn't see any further drop in the level.

 

[jonespj]

Re: coolant blowing back into overflow resevoir

Thanks to both of you for the advice. I'll do those 3 tests but is there a prefered order for 'em. Also how much do I pressurize each cyl. This engine is a 2 yr. old re-build I bought from a remanufactering co. so I hope it's not the head gasket already but with a rebuild I know anythings possible. Thats why I was leaniing towards the problem being something I missed when putting the maifolds etc. on. I appreciate the come backs

 

[nola mike]

Re: coolant blowing back into overflow resevoir

Don, would that indicate a head gasket leak, or were you thinking of something else?

 

[achris]

Re: coolant blowing back into overflow resevoir

Cylinder leakdown will be the most indicative (pressure 60-80psi)... That will probably be the most useful, but no preferred order... When you first fired up the engine from 'new', did you re-torque the head bolts? If you didn't, and it's not a 'mono-torque' type gasket, that could account for a leaking head gasket...

Chris.......

 

[jonespj]

Re: coolant blowing back into overflow resevoir

In referance to Don...When I installed the exaust manifold the mating surface to the elbow was bad on both the E.M. and the elbow. I put on a new elbow and new gasket but just used a file and some fine emory paper to get the E.M. shiney but the E.M. walls were really thin and one was slightly recessed/lower than the rest. I used ( I think?) hardening sealer thinking that might compensate for the condition of the E.M. but now I don't know if any of that was the right thing to do. So now I was wondering maybe thats the culprit. Since the head gasket and head was installed at the remanufacterer I didn't think that would have failed but I realize it is something that needs to be checked. Also re Chris... No I didn't re-torque the head. I do remember the fellow I talked to when I purchased the engine telling me that wasn't needed. Whether he was correct or not I dont't know. I cant recall the company right now but maybe I should call and see about that even though it is what it is right now. If they were not mono torque I guess its too late for that now right? Thanks

 

[jonespj]

coolant blowing into overflow bottle , engine not really hot

coolant blowing into overflow bottle , engine not really hot

Hello Fellow Boaters; Hey, I have a 1984 mercruiser 3.7 L and when I run at half throttle or better the coolant starts blowing back into overflow bottle. The motor don't have to get very hot for this to happen and I would think the coolant would be scalding hot but I can hold my finger in the bottle and its hot but not so m,uch that I have to jerk away. Ya'll suggested a leak down test a couple weeks ago and I finally got one and here are the results. No bubbles came up into the elbow coolant. Maintaining 80 lbs pressure on the guage the leakdown guage showed 20 to 25% on #1 and #4 cyl. and 35 to 40 at #2 and #3. I had it hooked up in ea. cyl about 3 min. ea. I think my exaust manifold is bad,( the mating surfaces were very thin when I installed it last year on this factory rebuilt eng.) I did buff them down to shiney metal and put on new gasket for elbow but I remember part of the surface seemed lower than the rest. I replaced the elbow but now wished I had replaced the manifold as well. I'm in the process of ordering another manifold. If that gasket and manifold is shot could that cause the coolant problem. One other thing that may help with diagnosis' it does have a very slow leak in the cooling system somewhere. I can fill the elbow up with antifreeze/water and when cap is off, about a half a cup will leak out in a week or so. I,ve looked all over and can,t find it . With the cap on tight it doesn,t leak as much but when I remove it I hear a hissing from the vacumm that its causing. Sorry for such a long description. Any help or suggestions would be appreciated. Thanks Paul

 

[vxtech]

Re: coolant blowing into overflow bottle , engine not really hot

Re: coolant blowing into overflow bottle , engine not really hot

unexplained coolant loss and increase in cooling system pressure sounds like headgasket failure

 

[Don S]

Re: coolant blowing back into overflow resevoir

I merged your two thread together, now everyone knows what was done and recommended before.

Not really a good idea to start a new thread when you are just updating a previous thread.

 

[jonespj]

Re: coolant blowing back into overflow resevoir

Sorry about the new thread, wasn't sure about the protocal and at the time I didn't see how to continue the original thread but now I got it. Thanks for the reccomendation about the head gasket vxtech! Does anyone else have a comment about my next step to solve the coolant problem or is it agreed that head gasket is most likely the cause. Also why wouldn't the leakdown test have shown bubbles in the coolant?

 

[nola mike]

Re: coolant blowing back into overflow resevoir

Did you do a coolant pressure test? Also, in case you don't know, some flow into the overflow reservoir is normal as the engine heats up...

 

[Bt Doctur]

Re: coolant blowing back into overflow resevoir

is this 2 barrel or 4 barrel

 

[jonespj]

Re: coolant blowing back into overflow resevoir

I have not done the coolant pressure test. I was going to borrow one but that didn't come through so I'm go purchase one, Thats a good thing to have anyway. As to the overflow its really a lot! It filled up the have full overflow jug and and another quart or 2 ran out.

Its a 2 barrel carb.

 

[stonyloam]

Re: coolant blowing back into overflow resevoir

Autozone will loan you one.

 

[jonespj]

Re: coolant blowing back into overflow resevoir

Thanks for the tip.

 

[jonespj]

Re: coolant blowing back into overflow resevoir

I pressurized the cooling system & it slowly loses pressure (about 5 min). I kept the psi at 15 -20 for 30 min. could not find an external leak so with plugs out I spun the engine (I loosly put paper towel over each plug hole) and still no sign of water. None coming out through fresh water inlet at lower unit either. Oil looks perfect but don't know how much it takes to get milky. If the head gasket is bad wouldn't the coolant go into one of the cyl. ?? Also when I did the leak down test it seems like if the head gask. is bad bubbles would almost have to come out into the coolant or maybe it only happens when engine is hot and the cyl. pressure is greater than the leak down test pressure. I know some coolant is going somewhere and plan on keeping the cooling sys. under pressure for an extended time to see if I can locate it. I was just hoping to know for sure that it is the head gasket before pulling it all apart. If its a cracked block I think I'll just get rid of the boat. I was hoping one of you could give me some info on this . Thanks for all the input. Paul