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1993 OMC/Volvo Ford 5.0 FI overcooling: Stays in limp mode when water is too cold.

I think you will find the same engines were marinized by PCM (Pleasure Craft Marine) and there is some service data out there if you look.

If the engine is running on the cold side and you know that the t-stat is good, I'd suspect the restriction in the thermostat bypass circuit is missing on a RWC engine...
 
In 1993, this would still be OMC.
As of sometime around or during '94, this would have been Volvo Penta.
Nonetheless, they both very likely used a similar thermostat manufacturer.

The thermostat by design holds back coolant (aka raw water coolant) until temperature dictates.
Only then will it allow coolant to escape and be replaced as needed.
If your engine temp is good, perhaps look towards a faulty FI temp sensor.


  1. Well, imagine my surprise today when, after installing a faucet at the raw water inlet of each engines and closing it quite a lot, both engines stayed in the 155F range
    and I was able to ride 1.5 hours using just about 10 gal of gas... (Vista 278).


  2. So it seems that the Volvo original t-stats are not able to cope with the
    pressure they are under and simply stay open...

  1. Why are you installing any type of faucet at the raw water inlet of each engine????

  2. These thermostats are temperature activated... not pressure activated.

    And again, in 1993, this would be OMC, not Volvo Penta. Even if it was Volvo Penta, all of these T stats are extremely similar in function.



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Hi Ricardo, and thank you for your reply.

They are in fact OMC, however it seems that they are the same engine used by Volvo
and I get Volvo parts when I order nowadays.

The engines are chronically overcooled and I have verified this with
with an IR thermometer. If you click on the link at the top, you will see
what I did.

As many hinted, when I removed the t-stat housing, I fully expected to find a cloged
bypass. But no, it was very perfect clean and quite large. So using the faucets
was to reduce the pressure in the system so the t-stat spring would be able to keep it
closed. And it worked. I came to this conclusion because the engines never got to even 160F
which is when the t-stats open...

Also, I noticed that recent t-stats for a 5.0 GXi for example, the spring
is MUCH stronger than the ones I have.

So, by lowering the pressure in the cooling system, the t-stats were able
to stay closed and bring the engines up to 160F and stopping the engines
from thinking the ECT sensors were bad.

What I know:
The t-stats work fine in a cup of hot water.
The open around 159 and are full open at around 178F.
The engines work perfect when they reach 150F minimum.
Without the faucets, brand new t-stats installed by the
marina mechanic (carefully cleaned seats and lubed oring),
the engines were not able to go up past 140F in 65F water...

I hope this helps shed light on this very peculiar problem.

If you want more details, the EEC-IV from Ford had a cold map
which then passes over to economy map when the engines reach 150F
at the sensor. However, there is also a timer that starts when the
engines lite up: After 15 minutes, if the ECT do not reach 150F,
the map declares the ECT bad and goes into limp mode (FMEM).
This is the issue I am trying to solve...

So I have two options that I see:
reduce the system pressure at the inlet hose, or try and install
a recent t-stat housing with a modern t-stat that works
well in this high pressure environment...
 
I think you will find the same engines were marinized by PCM (Pleasure Craft Marine) and there is some service data out there if you look.

If the engine is running on the cold side and you know that the t-stat is good, I'd suspect the restriction in the thermostat bypass circuit is missing on a RWC engine...

Hey Mak.

This is what I though also.
However, a bypass in a marine engines works in reverse
from a car engine: The bypass takes raw water and gets it
straight to the exhaust.

So in the even of overcooling, it is because the bypass is actually
clogged and forcing all the water through the t-stat.
I suspect this is built this was so you do not blow your engines if
the bypass clogs.

In my case, I fully suspect my s-stats to be car type where
the pressure in frin and in back of it is the same, or similar.

I was surprised how easy they are to open using just thumbs
and indexes from both hands...
 
Ricardo, if you know these engines and want to take a step back,
my issue is cronic overcooling. Where would you start from there?
T-stats are new and carefully installed, though in old housing (fresh water only),
and my bypasses are clear...

Thanks again for your replies!
 
Ricardo, if you know these engines and want to take a step back, my issue is cronic over-cooling. Where would you start from there?
T-stats are new and carefully installed, though in old housing (fresh water only), and my bypasses are clear...
I'd actually want to see what's going on with your cooling system layout, but I'll offer a stab at it here.

The bypass holes are clear as well as all other holes in the housing.
Other holes as in the ports for the exhaust manifold/elbow water, etc.?

So it seems that the Volvo original t-stats are not able to cope with the pressure they are under and simply stay open... can deal with the pressure encountered when an impeller pushed 30+ psi in the system...
Where/how are you measuring 30 psi from the impeller pump?


As many hinted, when I removed the t-stat housing, I fully expected to find a cloged
bypass. But no, it was very perfect clean and quite large.
Photos please.


If the engine is running on the cold side and you know that the t-stat is good, I'd suspect the restriction in the thermostat bypass circuit is missing on a RWC engine...

Mark, I'm thinking that there should be no need for anything other than the small air bleed hole in the thermostat flange...... (RWC system that is).
(shown in second image).

thermobasic.jpg


W01331672748GAT.JPG


See image at bottom of page.



Image of Ford 5.0L and 5.8L raw water cooling t-stat housing.
Yours may not be this exact style. Please post a few photos of yours.

BARMC29-63588.jpg



I know that yours is OMC, but FYI.
Years ago Merc did use the by-pass to ensure that the exhaust system received water during warm-up prior to the thermostat opening up.

Depending on the system, if the T-stat housing's mixing chamber provides continuous exhaust water, the thermostat area itself may not be required to offer any by-passing coolant.
But again, I think that I'd want to see a schematic of your system.

2011-12-08_211920_cover.jpg



With this style system (below), I don't believe that the by-pass port is required.
Incoming sea water is blending with the engine block's spent sea water via the T-stat housing's mixing chamber.

56601.gif




It would be nice to see some photos.

***********************************

This is a GM SBC T-stat housing.
The mixing chamber principle should be similar to the Ford's T-stat housing.

Blue = incoming sea water
Red = tempered water leaving engine block as per what the thermostat dictates
Blue/Yellow = blended water (within the mixing chamber) headed for the Circulating pump
Red/Blue = blended water headed for the exhaust system on a continuous basis
 

Attachments

  • RWC T Stat housing.jpg
    RWC T Stat housing.jpg
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Wow Ricardo, thank you for the effort in your reply.
My system is exactly like the last two images.
Also, I have the narrow t-stat shown. I do not have pictures of the
of my housings but the last picture is of that same hosing.

The pressure I assume is from the inlet hose. I actually did not do the hose up
water level test. This will be done next week-end.

One of the reasons I suspect the t-stats are not able to hold the pressure,
is that with the faucets, I actually see small fluctuations between 155F and
165F at the t-stats. I can only assume that, when I open the faucets,
the t-stats is then held open by the pressure difference between the
front and the back of the circuit...

One other note: I DID notice a small v-shaped notch on the old
t-stats I removed in the spring (They were blocked open).
The new ones had no such notch.
This is the thermostat here:
http://proboatparts.files.wordpress.com/2011/06/barr-omc-29-383307-160-degree-thermostat.jpg
As you can see, the spring has a lot of coils and the spring gauge
seems weak compared to the one you are showing, though it is a 195F...
 
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The PCM manual I have is a direct lift from FORDs manual so I doubt any significant change was done when the engines were marinized.

You don't want any gate valve in the raw water inlet to the pump...my earlier comment about the "bypass circuit" didn't mean the notch on you thermostat but rather the method used to slow the exit of cooling water so it can actually cool the block. Where and how the circuit works depends upon the configuration of your system.

As far as the SLOW circuit, it is wired just like an audio warning system's set of switches...you can disconnect them and insulate their terminals and the computer shouldn't enter SLOW mode.

Your timer mode before entering FMEM is partially correct...the FORD document indicates the timer's duration is set by the ambient temp when the key is turned on...
 
Back to you in blue text..............................

Wow Ricardo, thank you for the effort in your reply.
You are welcome. I wish that I knew more about this for you.

My system is exactly like the last two images.
Also, I have the narrow t-stat shown. I do not have pictures of the of my housings but the last picture is of that same hosing.
The last image is a GM SBC T-stat housing. Somewhat similar in function, however.

attachment.php


The pressure I assume is from the inlet hose. I actually did not do the hose up water level test. This will be done next week-end.
I believe that flexible vane impeller pumps do not reach near 30 psi.

One of the reasons I suspect the t-stats are not able to hold the pressure, is that with the faucets, I actually see small fluctuations between 155F and
165F at the t-stats. I can only assume that, when I open the faucets, the t-stats is then held open by the pressure difference between the front and the back of the circuit...
As Mark suggested, you do not want to interrupt the sea water flow to the sea water pump.

One other note: I DID notice a small v-shaped notch on the old t-stats I removed in the spring (They were blocked open).
The new ones had no such notch.
This is the thermostat here:
http://proboatparts.files.wordpress.com/2011/06/barr-omc-29-383307-160-degree-thermostat.jpg
As you can see, the spring has a lot of coils and the spring gauge seems weak compared to the one you are showing, though it is a 195F...
Is this an OEM replacement?





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BTW, I'm thinking that the three of us may perhaps be talking about a different by-pass port.

The by-pass porting that I've been speaking of is an actual port that allows some coolant (aka sea water... river/lake/ocean) to escape around the thermostat.
Some of these ports are anywhere from 1/4" to 3/8".
Some of the automotive engine ports are even larger.
However, these automotive ports direct the coolant back to the engine circulating pump where BTU loss is minimal.
(see image below)

Whereas with the Raw Water cooled marine engine, any sea water lost via the by-pass port, is a total loss.
It does not return via the circulating pump. Instead, it's directed onto the exhaust system and out with the exhaust gasses.

As I mentioned, the thermostat's job is to hold back coolant until the temperature dictates that the thermostat begins to allow coolant to leave the engine block/heads.
IMO, if your by-pass porting is too large, you may not be able to increase engine temp with a thermostat temp range increase.
You may need to restrict the by-pass porting some.

Just a thought!




Here's an automotive closed cooling system T-stat housing. Note the rather large by-pass port and hose.
This directs the by-pass coolant to the Circ Pump.

5sm.png
myqbwE1muTppzdIlUYb0n7Q.jpg


If the above was applied to a Raw Water cooled Marine engine scenario, this loss of coolant may prevent the engine from reaching the correct temperature.
IOW, it may be as simple as too much coolant being directed past the thermostat.

Mark, does that make any sense to you?


I'd like to see a photo of your Marine engine T-stat housing.


*****************************************

BTW, the GM SBC T-stat housing mounts to a horizontal intake manifold surface.......

$(KGrHqYOKj!E5W9!lpC!BObkYYntgw~~60_12.jpg


..... whereas the 5.0L and 5.8L Ford T-stat housing mounts to a vertical intake manifold surface.

mo033hAyLnPBbNIOKa3WHkA.jpg




.
 
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Good afternoon guys, and than you again for your help thus far.

To answer the last email, I am also talking about the bypass hole
that is letting water from the impeller straight out to the exhaust cooling hoses.

In the housing I have, the bypass hole is about the size of my pinky finger
while the engine side hole is about my thumb. So 1/4 inch vs 1/2 inch.

Because of the recess where these holes are, there is no easy way to accurately measure them...

To answer the previous post, even though this is a GM housing, it is identical in every way
to the OMC and VOLVO housing used on Ford engines...

Also, the housing in mounted top side, but on a 90deg bend tube just like part #1 on the OMC
parts diagram. So the part diagram, provides matches my engines perfectly.

For the record, the faucets are after the impeller, before the housing on the inlet side.

Regards.
 
Hard to say without looking at it...some of the old ford blocks had t-stats with an air bleeder and the notch was used to align the t-stat when it was installed so the bleeder was at the top...This helped to bleed any trapped air when the system was filled with coolant...I've seen a few aftermarket t-stats where the notch was pretty deep and no bleeder present. The theory goes that those t-stats used the notch itself as a bleeder
 
Ah, those where for closed cooling only?

Hmmm....

Well, I guess I will research how to install a mid 2000 Volvo
t-stat housing... The mount is identical, but my 90deg outlet
to mount the t-stat will not let me install a t-stat like shown...

Only a few weeks left, so I guess I will have all winter to figure it out :)

Thanks again for your insight on this matter :)
 
As for the bronze/red handle valves...... are these gate valves or stop valves?
A gate valve will fully open the thru-port.... whereas a stop valve is much more restrictive.
Just an FYI for you.


Also, where you have the gray plastic fittings....... when we shut down, you'd be surprised at how much residual heat will travel towards this plastic pipe fitting.
I've seen these use, and I've seen them darn near melted and softened beyond use.
Just an FYI for you on that.


Honestly, these parts have no business in a Marine environment.


.
 
I totally agree.

They are already removed.
The point was to confirm that engines at the correct temp worked perfectly
and I had no other issues.

This was confirmed, so come spring, I will use two different ways
to mount the tstats in the housings and pick the bext of the two.
Then I will have a long term solution to keep my engines running warm
and smooth :)
 
The housing that MichiganMotors lists, fits these applications.

New thermostat housing made to work in late model Volvo Penta (1992-current) and OMC (1990-1999) applications. Made for 4.3L, 5.0L, 5.7L, 7.4L, and 8.2L engines.Gasket and thermostat included in package (part #18-3677).

572_K_1_site_250_187.jpg


I think that we need to see your actually thermostat housing for the Ford engine application.


.
 
Well, I was able to finally fix my issues!

Without changing any parts, I disassembled the therm housings and installed
cork gaskets I made from 1mm think cork blank sheets.

I used an Olfa circular cutting tool.

Now both engines go up to 150F and I see when the terms open up.
Gas consumption went down to a minimum, so I am very eager to
get back at the helm this week end!

For anyone with the same issue, use a wire brush on a drill
to clean the thermostat mating surface and the O-Ring groove.
Then, put the cork gasket on the termostat and push the thermostat
only the mating surface. Using a large flat blade screw driver, push
down on the thermostat, compressing the gasket, while twisting the
O-Ring into the groove.

Worked perfectly and was very inexpensive...

Now, I have another problem: My engines being optimal, I have
a lot of prop slip :)

Happy boating season to everyone!
 
I had an 888 per the first picture. Then I hopped up the engine including 4 inch center riser exhaust manifolds. I looped the lower exhaust manifold cooling circuit into itself. Everything works fine, but the octopus appears to be eating two of its own limbs. How should I clean this mess up?
 
I had an 888 per the first picture. Then I hopped up the engine including 4 inch center riser exhaust manifolds. I looped the lower exhaust manifold cooling circuit into itself. Everything works fine, but the octopus appears to be eating two of its own limbs. How should I clean this mess up?

This is an old thread from 2013.... last activity was 6/18/2014.

It's always best to start a new fresh thread.
 
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