What am I missing -- high temps

[hcooperrn]

I've read through quite a few threads here on overheating, sorry to add another one, tried just about everything I've read, what am I missing?

Symptoms -- While on the hose, temp climbs regardless, I've always shut it off when it gets close to 220*.

On the water, per a different post I made, if the thermostat is against the engine block, not up inside the housing, I can run all day, but it runs cold, at about 130*. As soon as I install it correctly, with the thermostat up inside the housing above the plastic spacer, temperature will climb.

What I've tried -- impeller is new and checked 3 times, three different thermostats (all opened at the correct temp when heated in water on the stove), trans cooler screen is clean, while on the hose good flow out both sides of the exhaust, surface temps of the engine are never above 120*.

What am I missing or not understanding? I'm assuming that good flow out of both sides of the exhaust means the manifolds are good (fresh water boat), and that because I can run with the thermostat against the block, the circulating pump is doing it's job.

What else??? I have a new temp sender on the way, though it seems like a low probability failure point. Can anyone confirm what the resistance should be off the sender, just to rule out the gauge?

Any ideas why it works when it isn't installed right, but warms up when correct? Thanks for the help, this board has been amazing in troubleshooting a lot of other minor issues!!!

[boatwakes]

To help you confirm if it's overheating, get a cheap laser thermometer and shoot temps while you're running it.You've got the funky mercruiser water distribution system and here's what I suggest you check: is the plastic spacer in the thermostat facing the correct direction? If not it will not allow enough water to pass out to the manifolds and overboard when the thermostat opens and the water distribution manifold will subsequently send more water directly to the manifolds and bypass flow to the block.

[hcooperrn]

Thanks for the reply -- I'll triple check the spacer, I installed a new one and I try to be careful to line up the bump on the spacer with the slot in the housing; I'll triple check that I don't have it upside down, though.

Can you help me understand how the flow is supposed to work? I'm wondering if that's part of the clue I'm missing. The temp is low in the lake when the thermostat is against the block, below the spacer -- could this be artificial, and I'm simply allowing cold water to bypass the block, keep the sender cool, and it just goes overboard? If I'm understanding the way it is supposed to work -- the thermostat should be keeping water circulating through the whole system, and when it opens, it allows more water to go overboard?

I've been using a laser thermometer -- the dash gauge is usually about 10 degrees higher than anything I can find on the housing or the block. I checked the resistance on the sender in a pot of water on the stove last night; based on the Seloc values, it is reading 10-12 degrees low, so I'll get a new one.

Still doesn't explain why I can't run in any thermostat configuration when connected directly to my garden hose though? I've got good flow from the hose, but something about the pressure is related the issue, right? Or is it normal to get pretty warm pretty quick on a garden hose (straight connected through fittings and clear tube to the intake line).

[Chads972150]

I've always heard to put a trash can in the boat and fill it up with water put your suction hose in there then your garden hose in the can to keep the water level up as your garden hose cannot supply the correct amount of water

[hcooperrn]

Good call Chads -- I cut a hole in the bottom side of a trash can, added some 1" fittings and hose to 1 1/4" fitting directly into the intake line -- at idle, it sucked the water level down faster than the hose could fill it. I was able to run for about 5 minutes at a time and shut it off.

I found that after awhile, the gauge ran steady at 200*. However, after shutting it off, I quickly pulled the thermostat housing off and stuck a kitchen thermometer in the water -- 163*.

This is with a brand new sender, and the resistance was about 59 ohms, which should be in the 190* range if I'm reading the ranges correctly.

So next step will be to get a cheap temp gauge kit from the auto part store, hook it up, and see what temps I get.

Any other ideas? Of course, my laser temp gun decided to quit working, though I never found a high surface temp previously when it was working.

[jslayde1]

I have the same issues going on. I replaced the sender and continued to have temp reading at around the 200 mark. I bought a gauge kit - which read perfectly at 160 for two straight days.

I ended up putting the original wire/gauge back together and it continued to read 200 ish.

So, I'm thinking this may be a grounding issue. I have looked all around the boat but can not find anything that would indicate a bad ground...

hcooperrn - let me know if you come up with anything...i'm still chasing this one...

[hcooperrn]

Will do -- I'm not certain, but I don't think it's a ground issue -- when I checked the resistance on the sender with a multimeter, I had the positive clipped to the post and the negative touching to the sender itself, measuring the resistance directly. Clipping to metal on the block only added about 2 ohms of resistance.

My sender is new, though it is Sierra, not original Mercruiser.

I won't be able to try a gauge kit until Friday or Saturday -- did you try an electrical or mechanical kit?

[jslayde1]

I bought a Faria sender for mine - after I bought a cheap "non-marine" sender. Same results on both.

The reason I'm leaning towards a grounding issue (on the gauge/under the helm) is the resistance on the sender is consistent with the chart up from nominal temp to 160ish when measured at the motor. For troubleshooting, I have also wired in a separate wire from the sender to the gauge - with the same results, temp on the gauge moved towards the 200 mark.

On my issue, its seem the system is working (temp rises consistently) just reads a little too high. This is why its making me think grounding...

Either that or the gauge is bad.....

Here is the gauge kit from NAPA ( I think) - its a hard wired mechanical gauge. Read 160*.
IMG_2823.JPG

[hcooperrn]

Which chart are you using for resistance values? What resistance are you seeing at the sender when you are at 160*?

[jslayde1]

The Faria website has some good info on it - should help you a little even if you don't have Faira gauges. Try this:

http://faria-instruments.com/site_manuals/IS0085E.pdf

I don't remember exactly: At ambient temp the reading was around 1200 I think. When at 160* the reading was about 113 if I remember correctly. Should have been real close to the chart.

You can also google resistant values for coolant temp that will pull some charts up.

[hcooperrn]

Hooked up a mechanical gauge -- with everything installed correctly, temp was 160-165* all day long, even though the dash read 190*.

So my next step will be to get the Faria sender (which does have different resistance values). If that doesn't work, I'll be caught up with you jslayde and looking for a ground issue at the helm.

I think there's another thread with a similar problem and Chpthril recommended doing a voltage drop test. That's going to be a challenge with the mess of wires under my helm; it looks a bit hacked up to me. From what I can tell I have several 10-12 gauge red and black wires coming from the back to sort out which is true B+ and B-

[Middy]

Im going to throw this out because it is similar to an issue I had with my Marine Power 5.7L earlier this year. At idle in the water or connected to the fake a lake, the cooling system would not pump enough water through to cool the engine. However, on plane cruising around it seemed to keep up and motor would stay at normal temps. After spend 2/3 of my day trying to figure it out myself i threw the towel in and took to the local shop who said he could look at that night and likely have me back out on the water the next day sometime.

The mechanic identified it as the Water Pump Seal had gone bad, essentially allowing just enough air in the system and not allowing it prime under 2000 rpms, but above that no problems. Turns out that if thats the problem, the water pump needs to be replaced in whole, but all said in done it solved the cooling problem and we were back on the water the next day by noon!!

[hcooperrn]

Good thing to check, I'll take a look at it. Using the garbage can method, I'm able to idle and keep the temp steady, so I think I'm ok. Leaning more toward a bad sender/bad ground issue at this point -- I think getting the right t-stat in the right way with a new spacer has the engine at the right temp, I just need to gauges to match readings now and be believable.

[ChrisSnow]

as you are USA based unlikely, but... senders for the EU market have different ranges that correspond to the resistance.

have you definitely got a US sender? if your ohm readings don't match the curves then all i can suggest is try another! theres not really much to go wrong in them though....

[hcooperrn]

Small update -- I ordered an American Standard Faria brand sender to compare to the new Mercruiser sender. Doing the hot water test, the Faria values were just about perfect with the Faria spec. The link above posted by jslayde1 has the Faria resistance values. Side by side, the resistance values were different in the pot of hot water.

Out on the lake all weekend, and the reading was 175* steady all the time. I still think this is a bit higher than actual, so my next course of action will be working on the grounding under the helm to see if I'm adding extra resistance. My fuel gauge is pretty erratic, so I'm guessing there's something loose somewhere adding to the mix.